DOS Times March-April 2023

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 48 49 Accuracy ORA overestimates IOP compared to Goldmann Applanation Tonometry and the difference increases at higher IOPs.[10] Tono-Pen The Tono-Pen (Reichert Technologies, Depew, NY, USA) is based upon the MacKay- Marg principle.(Figure-9) The instrument consists of a 1.02 mm diameter plunger and a broad footplate. The plunger has a moveable tip, which when pressed against the cornea, generates a force detected by a strain gauge. The change in force is traced into a waveform and is analysed to give IOP readings. This tonometer can take multiple readings in few seconds and usually gives an average of the ten IOP readings taken with less than 85% variability are acceptable. After anaesthetising the cornea, the tip of the Tonopen is covered by a disposable sleeve. The instrument tip touches the cornea and makes an audible click for a satisfactory waveform and reading. The instrument gives the average of ten readings with variability score. The disposable tip must be changed between patients. Tonopen underestimates the IOP above 17mmHg and overestimates IOPs below 17mmHg and in thick corneas.[11] Tonopen can be used for measuring IOP in corneal opacity or corneal transplant eyes or even through bandage contact lens. Figure 9: Tonopen. Figure 10: Parts of Schiotz Tonometer. Schiotz Tonometer (Indentation Tonometry) Schiotz tonometer was developed by Hjalmar Schiøtz, the first director of the Eye Department at the Rijks Hospital in Oslo in 1905. It is an indentation-based tonometer, which is used in supine position. It has a weighted metal plunger that rides inside a metal cylinder attached to a footplate. The footplate is curved to match the corneal curvature and rests over the cornea while measuring IOP. The plunger is attached to a pointer with a scale. The plunger, barrel, and needle weigh 5.5g, this can be increased to 7.5g/10g/15g by addition of appropriate weights. The more the plunger indents the cornea, more the scale reading. (Figure-10) Procedure The tonometer tip and footplate should be wiped with an alcohol swab and let dry. The patient lies supine and the cornea is anaesthetised using topical anaesthesia. The patient is asked to fixate on his own thumb as a fixation target, right above the test eye. Patient must be explained that the procedure is essentially painless and should avoid blinking during the procedure. The examiner gently retracts the eyelids of the patient and tonometer is directly placed over the patient’s eye, perpendicular to the cornea. The measurement is noted to the nearest 0.25 scale units. If the scale reading is less than 3 units, additional weight is added to the plunger. Take a minimum three IOP readings, see the Friedenwald nomogram and average of the readings is noted as IOP. The instrument should be calibrated before each use by placing it on the metal sphere and it should show a reading of zero. If the reading is not zero, the instrument requires repair. The instrument should be rinsed with water, followed by alcohol wipe, and dried. Subspecialty - Glaucoma

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 50 51 Figure 11: Dynamic contour tonometer-slit lamp mounted contour tonometer gives Systolic, Diastolic IOP and Ocular Pulse Amplitude (OPA). Figure 12: iCare Home tonometer. Accuracy The Schiotz tonometer is heavy and itself raises the IOP when placed over the eye. This rise in IOP is influenced by the ocular rigidity. The reference tables assume normal ocular rigidity and give IOP conversion. However, eyes with high ocular rigidity like Hyperopes or long-standing glaucoma give falsely high IOP with Schiotz and eyes with low ocular rigidity like high myopia or operated RD surgery give falsely low IOP. The Pascal Dynamic Contour Tonometer (DCT) The Pascal® Dynamic Contour Tonometer (DCT; Swiss Microtechnology® AG, Port, Switzerland) is a slit lamp mounted tonometer, introduced in 2002. It is a non-applanating, contact tonometer. Principle The tonometer tip matches the contour of the cornea of the patient and the tip probe measures the eye-wall pressure. It is postulated that the intraocular pressure is directly transmitted to the cornea and the sclera, hence by matching the corneal contour and estimating its pressure, the instrument can measure the IOP inside the eyeball. The IOP is recorded and displayed at a LCD screen attached to the tonometer. (Figure-11) DCT measures IOP in real time and gives a pulsed curve with the cardiac cycle, the IOP is measured as the average of the lower waveform readings of the pulsed curve. It also indicates the difference between the maximum IOP and minimum IOP as the Ocular Pulse Amplitude. Ocular pulse amplitude has been found to be more in glaucoma compared from normal individuals. Accuracy DCT shows good agreement with Goldmann Applanation Tonometry. DCT is not affected by corneal thickness or previous refractive surgery. DCT performs better than GAT in thinner corneas.[12,13] Rebound Tonometry (iCare) The rebound tonometers use an electromechanical method for measuring the intraocular pressure using a return-bounce motion. The principle of rebound tonometry was introduced in 1931 by Obbink et al, but only in 1997 a portable, workable iCare tonometer was introduced. iCare tonometer uses a steel projectile covered with a plastic mushroom shaped tip. The tip has a radius of 0.9mm and a weight of 26.8mg. The device has two coils, a solenoid propelling coil and a sensing coil placed around the magnetized central probe. The movement of the probe induces a voltage that can be sensed by the sensor probe. When the probe impacts the cornea, the deceleration of the probe is measured as IOP. No corneal anaesthesia is required. The instrument takes six readings and the average of the readings as IOP. iCare HOME tonometer (Figure-12) is being used for home tonometry by the patients.[14] iCare tonometer shows a mean difference from GAT of less than 1mmHg, the difference increases in patients with higher corneal thickness.[15] Trans-Palpebral Tonometry Easyton® transpalpebral tonometer is a portable tonometer which consists of an IOP measuring vibrator rod, which is used to test IOP over the eyelid. (Figure-13) This rod is surrounded by a protective ring. It can be switched between two measuring modes : Maklakov and Goldmann. The IOP measuring range is upto 53mmHg. The tip can be easily cleaned using alcohol wipes between use. It has displayed moderate to good agreement with Perkins tonometry and can be used in children or uncooperative patients for screening.[16] Subspecialty - Glaucoma

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 50 51 Figure 13: Easyton® transpalpebral tonometer. Figure 15: Parts of TriggerFISH contact lens sensor : 1. Ocular Telemetry Sensor 2. Antenna 3. Data Cable 4. Recorder. Recent Advances in Tonometry Figure 14: Convex prism for GAT in Post LASIK cornea. Modified Goldmann Applanation Tonometer for LASIK Eyes[17] The applanation biprism tip modification has been done for measuring GAT in LASIK. The tip of the prism is changed from flat to convex with a radius of 13mm.(Figure-14) While doing normal GAT in normal corneas, there is force that is applied in the centre of the prism and cornea due to convexity of the cornea in normal state. This force is later spread to the edges of the prism. The corneal force exerted from the flattened central cornea is much lower in post LASIK or refractive surgery patients. When a convex prism is applied to the centre of post-Lasik flat corneas with a convex force, there is initial raised contact pressure in the 24-Hour IOP Monitoring Sensimed (Switzerland) has introduced a contact lens sensor (CLS), triggerFISH, to define IOP. This is a soft silicon disposable lens with a diameter of 14.1mm central thickness of 585 µm and has 3 base curves (8.4, 8.7 and 9 mm). It had an embedded strain gauge to measure IOP with an antenna.(Figure-15) The strain gauge can detect change in corneal shape and measure IOP. The lens can take 300 reading in 5 minutes and record the IOP.[18,19] It is also beneficial in determining the peak IOPs in glaucoma patients, most studies showing a nocturnal peak in all types of glaucoma.[20,21] centre like the normal cornea. This results in balance of forces similar to the normal cornea and accurate IOP measurement. Subspecialty - Glaucoma

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 52 53 Figure 16: The Eyemate-IO intraocular a ring-shaped pressure sensor implant. The Eyemate-IO intraocular version (Implandata Ophthalmic Products, Hanover, Germany) is a ring-shaped pressure sensor implant designed for ciliary sulcus placement during cataract surgery, permanently.[22] (Figure-16) It has four haptics at the outer edges and is available in varying diameters of 11.3, 11.7 and 12.1 mm; the inner diameter is 7 mm and the thickness is 0.5 mm at the edges. The ARGOS 02 trial has studied EYEMATEIO at 12 months after implantation. The IOP measurements were higher than GAT by mean 3mmHg, few mild to moderate ocular adverse effects.[23] ARGOS-SC Eyemate-SC suprachoroidal pressure sensor:[24] This sensor device is implanted in the suprachoroidal space in patients undergoing non penetrating glaucoma surgery. It is an invasive method of determining IOP. It is relatively contraindicated in glaucoma patients who won’t benefit from NPGS like neovascular glaucoma or baseline IOP>40mmHg.[25] The mean difference between Eyemate-SC and GAT was 0.8mmHg. In addition, a smartphone application allows the patient and the doctor (cloud-based sharing) to view the IOP, to track the pressure history. Episcleral Telemetric IOP Measurement An episcleral pressure transducer based on 6 capacitive pressure sensing units is embedded in a silicone biocompatible rubber encasement. A hand-held device placed in front of the eye less than 4cm distance can give telemetric readings of IOP. The dimensions of the implant is 9mm long, 6mm wide and 0.9mm thick, which is fixated in the subconjunctival space.[26] References 1. Goldmann H. [A new applanation tonometer]. Bull Mem Soc Fr Ophtalmol. 1954;67:474–7; discussion, 477–8. 2. Mark HH, Mark TL. Corneal astigmatism in applanation tonometry. Eye. 2003 Jul;17(5):617–8. 3. Ehlers N, Bramsen T, Sperling S. Applanation tonometry and central corneal thickness. Acta Ophthalmol (Copenh). 1975 Mar;53(1):34– 43. 4. Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol. 2000;44(5):367–408. 5. Bader J, Zeppieri M, Havens SJ. Tonometry. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jun 19]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK493225/ 6. Cordero I. How to verify the calibration of Goldmann tonometers. Community Eye Health. 2012;25(79–80):65. 7. Threlkeld AB, Froggatt JW, Schein OD, Forman MS. Efficacy of a disinfectant wipe method for the removal of adenovirus 8 from tonometer tips. Ophthalmology. 1993 Dec;100(12):1841–5. 8. Kaushik S, Pandav SS, Banger A, Aggarwal K, Gupta A. Relationship between corneal biomechanical properties, central corneal thickness, and intraocular pressure across the spectrum of glaucoma. Am J Ophthalmol. 2012 May;153(5):840-849.e2. 9. Kaushik S, Pandav SS. Ocular Response Analyzer. J Curr Glaucoma Pract. 2012;6(1):17–9. 10. Martinez-de-la-Casa JM, Garcia-Feijoo J, Fernandez-Vidal A, Mendez-Hernandez C, Garcia-Sanchez J. Ocular response analyzer versus Goldmann applanation tonometry for intraocular pressure measurements. Invest Ophthalmol Vis Sci. 2006 Oct;47(10):4410–4. 11. Bao B, Diaconita V, Schulz DC, Hutnik C. Tono-Pen versus Goldmann Applanation Tonometry: A Comparison of 898 Eyes. Ophthalmol Glaucoma. 2019 Nov 1;2(6):435–9. 12. Doyle A, Lachkar Y. Comparison of dynamic contour tonometry with goldman applanation tonometry over a wide range of central corneal thickness. J Glaucoma. 2005 Aug;14(4):288–92. 13. Francis BA, Hsieh A, Lai MY, Chopra V, Pena F, Azen S, et al. Effects of corneal thickness, corneal curvature, and intraocular pressure level on Goldmann applanation tonometry and dynamic contour tonometry. Ophthalmology. 2007 Jan;114(1):20–6. 14. Scott AT, Kanaster K, Kaizer AM, Young CC, Pantcheva MB, Ertel MK, et al. The Utility of iCare HOME Tonometry for Detection of Therapy-Related Intraocular Pressure Changes in Glaucoma and Ocular Hypertension. Ophthalmol Glaucoma. 2022;5(1):85–93. 15. Takagi D, Sawada A, Yamamoto T. Evaluation of a New Rebound Selftonometer, Icare HOME: Comparison With Goldmann Applanation Tonometer. J Glaucoma. 2017 Jul;26(7):613–8. 16. Montolío-Marzo E, Morales-Fernández L, Saenz-Frances San Baldomero F, García-Saenz S, García-Feijoo J, Piñero DP, et al. Easyton® transpalpebral versus Perkins applanation tonometry in different populations. Int Ophthalmol. 2023 Jun 7; 17. Iglesias M, Yebra F, Kudsieh B, Laiseca A, Santos C, Nadal J, et al. New applanation tonometer for myopic patients after laser refractive surgery. Sci Rep. 2020 Apr 27;10(1):7053. 18. Gaboriau T, Dubois R, Foucque B, Malet F, Schweitzer C. 24-Hour Monitoring of Intraocular Pressure Fluctuations Using a Contact Lens Sensor: Diagnostic Performance for Glaucoma Progression. Invest Ophthalmol Vis Sci. 2023 Mar 1;64(3):3. 19. De Smedt S, Mermoud A, Schnyder C. 24-hour intraocular pressure fluctuation monitoring using an ocular telemetry Sensor: tolerability and functionality in healthy subjects. J Glaucoma. 2012;21(8):539– 44. 20. Tan S, Yu M, Baig N, Chan PP man, Tang FY, Tham CC. Circadian Intraocular Pressure Fluctuation and Disease Progression in Primary Angle Closure Glaucoma. Invest Ophthalmol Vis Sci. 2015 Jul;56(8):4994–5005. Subspecialty - Glaucoma

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 52 53 21. Agnifili L, Mastropasqua R, Frezzotti P, Fasanella V, Motolese I, Pedrotti E, et al. Circadian intraocular pressure patterns in healthy subjects, primary open angle and normal tension glaucoma patients with a contact lens sensor. Acta Ophthalmol (Copenh). 2015 Feb;93(1):e14-21. 22. Enders P, Cursiefen C. Device profile of the EYEMATE-IOTM system for intraocular pressure monitoring: overview of its safety and efficacy. Expert Rev Med Devices. 2020 Jun;17(6):491–7. 23. Choritz L, Mansouri K, van den Bosch J, Weigel M, Dick HB, Wagner M, et al. Telemetric Measurement of Intraocular Pressure via an Implantable Pressure Sensor-12-Month Results from the ARGOS-02 Trial. Am J Ophthalmol. 2020 Jan;209:187–96. 24. Szurman P, Gillmann K, Seuthe AM, Dick HB, Hoffmann EM, Mermoud A, et al. EYEMATE-SC Trial: Twelve-Month Safety, Performance, and Accuracy of a Suprachoroidal Sensor for Telemetric Measurement of Intraocular Pressure. Ophthalmology. 2023 Mar;130(3):304–12. 25. Koutsonas A, Walter P, Roessler G, Plange N. Implantation of a novel telemetric intraocular pressure sensor in patients with glaucoma (ARGOS study): 1-year results. Invest Ophthalmol Vis Sci. 2015 Jan 22;56(2):1063–9. 26. Mariacher S, Ebner M, Hurst J, Szurman P, Januschowski K. Implantation and testing of a novel episcleral pressure transducer: A new approach to telemetric intraocular pressure monitoring. Exp Eye Res. 2018 Jan;166:84–90. Dr. Mohit Goyal, MBBS, MS Senior Resident, Department of Ophthalmology, Government Medical College and Rajindra Hospital, Patiala, Punjab. Corresponding Author: Subspecialty - Glaucoma

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 54 55 A Stitch in Time, Saves Nine: A Diagnosis in Time, Saves Life! Aditi Kochar, MBBS, DOMS, DNB, Surbi Taneja, MBBS, DNB, Pradeep Sharma, MBBS, MD, Harsh Kumar, MBBS, MD Department of Ophthalmology, Centre for Sight, New Delhi. Introduction When diagnosing glaucoma, ophthalmologists rely on disc findings, Optical Coherence Tomography (OCT) changes and visual field defects. A misdiagnosis can sometimes have serious consequences on the patient’s visiual outcome and overall health. Glaucoma is often over diagnosed and treated. It is important to distinguish between glaucomatous and non glaucomatous disc appearances and visual field defects. The dilemma arises when neuro-ophthalmological and glaucomatous appearances overlap, hence causing immense confusion in the mind of the ophthalmologist. It is difficult to distinguish between glaucomatous and non glaucomatous disorders but not impossible. Non glaucomatous optic disc cupping can be seen in compressive, ischemic and inflammatory optic nerve head disorders.[1] Non glaucomatous disorders affecting visual fields include neurological and retinal disorders. In such cases, a detailed patient history, workup and also a contrast enhanced MRI brain may help to reach a conclusion. Visual Acuity, pupillary reactions, visual fields, OCT of the Retinal Nerve Fibre Layer (RNFL) and Ganglion Cell Complex (GCC) also substantially assist in differentiating in the diagnosis between glaucoma and other masqueraders. Here we present a case of suspicious glaucomatous cupping with a superimposed neurological disorder, diagnosed just in the nick of time, thus saving the patient from the grave risk of suffering a stroke. Case Description A 64 year old male diabetic patient presented to our glaucoma outpatient department for a routine eye checkup. He had Best Corrected Visual Acuity (BCVA) of 6/6 and N6 in both eyes (BE). Patient had no family history of glaucoma. No history of sleep apnea, acute blood loss or hypotension. On examination the anterior segment was within normal limits in BE. Grade 1 Relative Afferent Pupillary Defect (RAPD) was seen in the Right Eye (RE). Fundus showed a Cup Disc Ratio (CDR) of 0.7:1 in the (RE) and 0.5:1 in the left eye (LE), with moderate nonproliferative diabetic changes in BE (Figure-1) His intra ocular pressure on Goldman applanation tonometer was 12mmHg in the RE and 14mmHg in the LE. Gonioscopy showed grade 3 open angles (Shaffers grading). The central corneal thickness was 500 microns in the RE and 498 in the LE. OCT RNFL was within normal limits (Figure-2). Visual fields showed Right homonymous hemianopic defects, with an incomplete superior arcuate defect and inferior temporal defect in the RE (Figure-3) and a superior arcuate defect with inferonasal defect (Figure-4) in the LE. Patient was advised an urgent contrast enhanced MRI brain as the visual field report was inconclusive and indicated a certain deflection towards a neurological defect. MR imaging revealed acute infarcts in the left cerebellar hemisphere with acute internal hemorrhages in the left occipital lobe and thalamus. Patient was immediately referred to a neurologist and was managed on priority basis. Figure 1: Fundus photo showing CDR 0.7:1 in RE and 0.5:1 in LE with no RNFL defect. Subspecialty - Glaucoma

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 54 55 Figure 3: Visual fields in RE showing incomplete superior arcuate and inferior temporal defect. Figure 4: Visual fields in LE show superior arcuate defect and inferior nasal defect. Discussion Glaucoma management involves much more than just the diagnosis of a patient. It can prove to be life saving at times. Neuropththalmological diseases can resemble glaucoma and often be misdiagnosed as Normal tension glaucoma (NTG). Non glaucomatous cupping can often be seen in compressive optic neuropathy. In addition to unusual visual fields, two other signs that are highly suggestive of neurological disorders are color vision deficits[4] and afferent pupillary defects (APD). APD is rarely seen in early or moderate glaucomas and if present can be a sign of asymmetric presentation of glaucoma. Visual fields are the most important investigation in the evaluation of glaucoma. However fields are affected not only in glaucoma but also in neurological diseases, optic nerve head anomalies and retinal diseases. Neurological fields have a specific characteristics that they respect the vertical midline whereas glaucomatous field defects respect the horizontal midline. However in cases with both the diseases, presentation may be varied with mixed field defects.[2-3] This can be confusing for the examiner. In our case the optic nerve cup disc ratio asymmetry pointed clearly towards the patient being a disc suspect. OCT RNFL showed no pre perimetric changes decreasing the probability of glaucomatous visual field defects. To our surprise, when the patient’s field reports showed mixed defects, we proceeded with advising contrast enhanced MRI due to the strong suspicion of homonymous hemianopia. The MRI revealed acute infarcts and immediately the patient was referred to the neurology emergency where he received timely treatment which was life saving. Figure 2: OCT RNFL showing no pre-perimetric changes in both eyes. Subspecialty - Glaucoma

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 56 57 The contrast enhanced MRI Brain revealed acute infarcts and immediately the patient was referred to the neurology emergency where he received timely treatment which was life saving. Conclusion One must note that appearances can be deceptive and what may appear only like glaucoma may actually be something more sinister. A thorough workup, ruling out possible neuroophthalmological disorders may also be required, as timely action may rescue a patient from grave complications. Thus concluding that, a stitch in time saves nine! References 1. Hildebrand GD, Russell-Eggitt I, Saunders D et al (2010) Bow–tie cupping: a new sign of chiasmal compression. Arch Ophthalmol 128:1625–1626. 2. Greenfield DS, Siatkowski RM, Glaser JS, et al. The cupped disc. Who needs neuroimaging? Ophthalmology. 1998;105:1866-74. 3. Fraser CL, White AJ, Plant GT, Martin KR. Optic nerve cupping and the neuro-ophthalmologist. J Neuro Ophthalmol. 2013;33:377-89. 4. Pacheco-Cutillas M, Edgar DF, Sahraie A. Acquired colour vision defects in glaucoma—their detection and clinical significance. Br J Ophthalmol 1999;83:12:1396-402. Dr. Surbi Taneja, MBBS, DNB Fellow Glaucoma and Cataract services Centre for Sight, New Delhi. Corresponding Author: Subspecialty - Glaucoma

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 56 57 A Study of Ocular Abnormalities in Children with Cerebral Palsy Indu Bala, MS, Rajeev Tuli, MS, Indu Dhiman, MS, R.K. Sharma, MS, Piyush Gautam, MD Department of Ophthalmology, Dr. RPGMC, Kangra at Tanda (HP). Introduction Cerebral palsy is a group of permanent and non-progressive disorder of the development of movement and posture which causes limitation in activity, that occurs during the development of the foetal or infant brain. CP is the most common cause of physical disability in early childhood and the overall prevalence is approximately 2-3 per 1000 live births.[1,2] Cerebral palsy may be due to developmental, genetic, metabolic, ischemic, infectious or other acquired aetiologies. There may be other developmental disorders like mental retardation, hearing disorders, visual disability, speech impairment, cognitive or behavioural handicap along with cerebral palsy.[3] Ocular milestones like fixation, stereopsis and accommodation are well developed by 4-6 months. Many ocular diseases have their origin in childhood and the morbidity may go unnoticed and may also cause severe ocular disability in later part of life. As vision is the most important sense for general development and education. The earlier and better the visual sense function, the greater the chance the child has achieved his potential.[4] The damage to the motor control in the developing brain can occur during pregnancy, perinatal or postnatal life. The resultant limitation in movement and posture can be accompanied by seizure disorder, abnormal muscle tone, dysarthria, sensory impairment, mental retardation and learning disabilities.[5] There are four main types, Spastic, ataxic, dyskinetic/athetoid and mixed cerebral palsy. The spastic type can be further classified into Spastic hemiplegia, spastic diplegia and spastic tetraplegia types. In the spastic type there is stiffness and movement difficulties, in ataxic form there is a disturbance of sense of balance and depth perception, while in the athetoid type there are involuntary and uncontrolled movements. Walking ability in children with cerebral palsy has been found to be significantly related to the type of cerebral palsy, IQ level, presence of active epilepsy and severe visual or hearing impairment.[6] Cerebral palsy is associated with an increased risk of ocular abnormalities especially remarkable are refractive errors, strabismus, nystagmus, amblyopia and cortical visual impairment which are observed in 50-90% of the patients with cerebral palsy.[7] Cortical visual impairment (CVI) refers to lesions in the posterior visual pathway (from lateral geniculate body to the visual cortex) and represents difficulty in processing and interpreting visual information in the visual cortex.[8] Neuroimaging in this group of children often shows lesions in the visual cortex called periventricular leukomalacia (PVL). CVI due to PVL is characterized by delayed visual maturation, subnormal VA, crowding, visual field defects and visual perceptual-cognitive problems.[8] The presence of CVI typically worsens the functional outcome in patients with CP.[9] The diagnosis of CP is usually made on the basis of uncoordinated muscle movements and delay in reaching developmental milestones.[10] In addition to a physical examination, computerized tomography and/or magnetic resonance imaging of the child’s brain to look for the brain insults and abnormalities may help to diagnose the condition.[11] The assessment and management of visual disorders in physically or intellectually impaired children present a complex challenge for the clinician. This study explores and documents the variety of ocular manifestations in children with Cerebral Palsy and educates the parents of these children concerning the importance of early and regular ocular examination, diagnosing the ocular problems and their appropriate treatment. Materials and Method This study is cross sectional study, descriptive and hospital based. The study was conducted for one year duration. All the patients were diagnosed with Cerebral Palsy by a pediatrician. Children aged between one to eighteen years already diagnosed with cerebral palsy were included in the study. Children diagnosed to have other disorders/syndromes apart from cerebral palsy which are associated with ocular problems, were excluded from the study. Informed consent was obtained from the parents/guardian prior to participation in the study. A detailed history regarding gestational age at birth, antenatal and the postnatal complications and any relevant treatment history was recorded. Detailed systemic evaluation was done by paediatrician and the type of cerebral palsy was determined. Every child was seated either on their parent’s lap or in adaptive wheel chairs throughout the examination. A detailed ophthalmic work-up was done. Depending upon the age and cooperation of the patients, a variety of methods including Snellen chart, Kay Picture test, and Central Steady Maintained technique (CSM) were used for assessing visual acuity. CSM involves covering one eye while the child is fixating on an object (small toy). The non-covered eye should maintain central, steady fixation, which is maintained through a blink. Ocular motility was assessed by highly interesting colorful objects or torchlight in six different Subspecialty - Neuro-Ophthalmology

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 58 59 cardinal gazes. In uncooperative patients, the Doll’s head tilt test was used to test extraocular motility. Binocular function as assessed by Hirschberg test, cover-uncover test, Krimsky test and Bruckner test. The laterality and constancy of any deviation were noted. Restriction of ocular motility as well as the presence of nystagmus were noted. Refraction under cycloplegia was performed in all the children. Cycloplegia was obtained with 1% of atropine eye ointment in children below 6 years and with 1% cyclopentolate in children between 6-18 years. Atropine ointment was used for 3 consecutive days applied twice a day in lower cul de sac of both eyes followed by retinoscopy on 4th day in children less than 6 years and one drop of 1% cyclopentolate in children between 6-18 years instilled every 15 min for 3 times followed by retinoscopy 15 minutes after instillation of last drop. The standards for quantifying refractive error were as follows: Myopia was considered to be a mean spherical equivalent of ≥0.50D, Hypermetropia as ≥ +1.00D, Astigmatism as ≥ 1.00D in any meridian and Anisometropia (mean sphere) as ≥ 1.00D. Hand held slit lamp or a standard slit lamp biomicroscope was used for a detailed examination of the anterior segment. Age group (in years) 1-2yrs 2-6yrs 6-18yrs Total no. of cases 6 22 13 Male 4 18 9 Female 2 4 4 Types Total Percentage No. of patients had ocular anifestations Spastic 33 (80.49%) 27 Athetoid 1 (2.44%) 1 Ataxic 4 (9.76%) 3 Mixed 3 (7.31%) 1 Table 1: Distribution of patients according to age and sex (n=41) Types of Cerebral Palsy The most common type of cerebral Palsy was spastic type present in 33 (80.49%) patients followed by ataxic type (9.76%). Risk Factors Out of 41 patients, History of antenatal risk factors was recorded in 16 (39.02%) patients. Out of 16 patients, six patients had H/O Pregnancy induced hypertension, one patient had Gestational Diabetes Mellitus, Five patients had Intrauterine growth retardation and four patients had fever without rash, out of these 16 patients, 14 patients had ocular manifestation. History of preterm delivery was present in eight patients (19.51%) out Distribution of patients according to type of cerebral palsy and ocular manifestations is shown in (Table 2). The assessment of posterior segment was done using direct ophthalmoscope or indirect ophthalmoscope after full dilatation of pupil. If patient was found to have reduced visual acuity despite normal ocular health, Cortical Visual Impairment (CVI) was suspected. Magnetic resonance imaging (MRI/CT) was done in selected cases. After informed consent, all the procedures were performed. Data thus collected was entered into an electronic database for statistical analysis (SPSS, VERSION 20.0). Data was presented as number (%) or mean (SD) as considered appropriate. Categorical variables were compared using appropriate tests and continuous variables using Student’s t test for independent samples. The p-value less than 0.05 was considered statistically significant. There was no conflict of interest. Results Age and Sex A total of 41 patients with cerebral palsy were included in the study. The mean age of the patients was 6.52 ± 4.89 years. Distribution of patients according to age and sex is shown in Table 1. Table 2: Distribution of patients on the basis of types of Cerebral Palsy (n=41). of which seven had ocular manifestation. 33 (80.49%) patients had full term delivery out of which ocular manifestations were present in 25 cases. History of postnatal events was present in 25 (60.97%) patients. History of asphyxia in six patients, seizures in two patients, asphyxia with seizures in 14 patients, jaundice in one patient, sepsis in one patient and hypoglycaemia in one patients was present, out of which 21 patients had ocular manifestation. Subspecialty - Neuro-Ophthalmology

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 58 59 Remaining 16 (39.02%) patients had no h/o postnatal events, out of which 11 patients had ocular manifestations. Visual acuity Visual acuity assessment was done using age appropriate Ocular Manifestations Ocular manifestations were present in 32 (78.05%) patients. Among the ocular manifestations the most common was refractive error present in 26 (63.41%) patients followed by Refractive Error The most common refractive error was astigmatism followed by hypermetropia and myopia. Distribution of patients on the methods. Presentation of visual acuity among all patients is shown in Table 3. All the patients with visual acuity ≤6/12 had ocular manifestaions. Visual acuity Ocular manifestation (present) Percentage Ocular manifestation (absent) Percentage overall Percentage 6/6-6/9 2 6.25 9 100 11 26.83 6/12-6/18 8 25 0 0 8 19.51 6/24-6/60 17 53.12% 0 0 17 41.46 <6/60 5 15.62% 0 0 5 12.19 Total 32 100 9 100 41 100 Ocular manifestations No. of patients Percentage Refractive error 8 19.5 Strabismus 1 2.44 Refractive error+strabismus 14 34.15 Optic atrophy 1 2.44 Nystagmus+refractive error 4 9.76 Nystagmus +optic atrophy 2 4.88 CVI 2 4.88 Total 32 Refractive Error Number Percentage Nil 15 36.58 Astigmatism 11 26.83 Hypermetropia 9 21.95 Myopia 6 14.63 Total 41 100 Table 3: Distribution of patients on the basis of types of Visual acuity (n=41). Table 4: Distribution of patients on the basis of types of ocular manifestations (n=41) Table 5: Distribution of patients on the basis of refractive error strabismus, present in 15 (36.58%) patients. Distribution of patients on the basis of types of ocular manifestations is shown in Table 4. basis of refractive error shown in Table 5. At the time of first ophthalmological examination only eight patients were wearing glasses. Subspecialty - Neuro-Ophthalmology

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 60 61 Binocular Function Binocularity was assessed using various tests according to the cooperation of children and feasibility for the examiner. Strabismus was present in 15 (36.59%) patients. Out of these 15 patients, eight patients had alternating exotropia, two patients unilateral exotropia, four patients alternating esotropia and one patient had unilateral esotropia. Among total patients, Nystagmus was present in six (14.63%) patients. Extraocular Motility Extraocular motility was assessed in 35 (85%) of the children. Out of them, 32 (92%) patients had full extraocular movements while three (8%) patients had restricted movements. Pupil and Optic Nerve Status Relative Affarent Pupillary Defect (RAPD) was present in three (7.3%) patients, sluggishly reacting pupil in two (4.9%) patients. Temporal disc pallor was seen in 20 (48.78%) patients, Hyperemic disc in three (7.32%) patients, Myopic fundus in two patients (4.88%) and diffuse disc pallor was seen in three (7.32%) patients. CT/MRI Findings Among total 41 patients, 23 (56.09%) patients had hypoxic ischaemic encephalopathy. One (2.43%) patient had cystic encephalomalacia in the right fronto parietal temporal lobe while another one (2.43%) patient had diffuse cerebellar and cerebral atrophy. Seven (17.07%) patients had normal scan. Nine (21.95%) patients did not have CT/MRI done. Discussion The prevalence of ocular manifestations in children with cerebral palsy differs from region to region. The problems associated with their vision is mostly neglected. The present study highlights the risk of ocular problems in children with cerebral palsy. A total of 41 children were enrolled for the final analysis in the study. The mean age of the participants was 6.9±5.11 years at the time of first ophthalmic examination. Out of 41 children, 31 (75.60%) were male and 10 (24.39%) were female with male to female ratio of 3:1. Marasini et al[12] evaluated children with the mean age of 5.48 ± 4.75 years in their study and have found similar sex distribution ratio. Males are more than females, moreover the gender distribution in studies can vary depending on the sample size. Spastic type cerebral palsy was the most common followed by ataxic, mixed and athetoid type as shown in Table 2. In a study by Katoch S et al[13] have found that 91.5% of patients had spastic diplegia. Spastic children are more likely to have ocular defects than athetoid and ataxic children. The pathology in spastic children is more extensive and diffuse, with periventricular haemorrhage, subcortical haemorrhage, and cortical atrophy as compared to more localised pathology in athetoid and ataxic children. The most common risk factor in this study was birth asphyxia (39.02%) followed by seizures (31.7%) and then prematurity found in 19.51% of patients. In a cross sectional study by Reena A. et al[14] birth asphxia, seizure and preterm were noted in 16.66%, 12.6% and 16.66% children respectively. Prolonged or intense asphyxia will cause energy depletion in tissues that are dependent on aerobic metabolism, such as the central nervous system.[15] Lack of energy can lead to the failure of ATP-dependent pumps resulting in the loss of neuronal transmembrane potential[16] and thus the most sensitive areas of the brain will die. Thus, irreversible brain injuries during early brain development might ultimately result in Cerebral Palsy. The accurate measurement of visual acuity in CP patients is a difficult job and different methods have been used for assessment of visual acuity in children. A varied range of visual acuity has been recorded in CP patients in this study as shown in Table no 2 and these findings are consistent with the literature.[17] The literature has reported the varied prevalence (15-58%) of ocular morbidities in normal children.[18] In our study ocular manifestations were present in 78.05% of children with cerebral palsy, similarily reported by Solomon C.B. et al.[19] The most common ocular manifestation seen in this study was refractive error (63.41%) and the similar prevalence of refractive error has been reported by other studies in literature.[13,20] In contrast to this, study done by Govind A et al[21] found strabismus (35.7%) to be the most common ocular abnormality. Astigmatism (26.83%) was the most common refractive error followed by hypermetropia (21.95%) and myopia (14.63% ) in this study and the results are comparable to another study in literature by Katoch S et al.[13] In India, Literature reports the prevalence of refractive error in normally developing children of school age is 8% (7.4-8.1%)[22] which is far less than we found in our Cerebral Palsy patients. This emphasizes the need for appropriate referral and management of refractive problems, and counseling of parents of the need for vision care in CP children. Strabismus was the second common ocular abnormality present in 36.59% of children. Among them exotropia was present in 24.39% and esotropia in 12.19% of CP children. These results are consistent with study conducted by Katoch S et al.[13] Other findings associated with cerebral palsy in the included nystagmus, CVI and optic atrophy. The prevalence of nystagmus (14.63%) in our study resembles with the other study in literature by Njambi L et al.[23] Optic atrophy was present in 7.32% of children in this study which is in accordance with the prevalence (5-10%) reported in literature.[13,21,23] Two (4.8%) children having very poor visual acuity not attributable to any ocular abnormalities were suspected of having either retrochiasmal or central cortical lesions. Cortical visual impairement (CVI) was seen in 2.4% patients in study done by Huo R et al.[24] In contrast to this, CVI was observed in 51.4% of the children in the study conducted by Elmenshawy AA et al[25] which was much higher as compared to our study. Conclusion This study was an attempt to assess ocular manifestation in children with cerebral palsy. Our study demonstrates Subspecialty - Neuro-Ophthalmology

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 60 61 high prevalence of ocular manifestations in children with cerebral palsy. This emphasizes the need for a proper ocular examination of all patients diagnosed with cerebral palsy. Early intervention will help for the child’s physical, social, academic and visual development. The parents/caregivers need to be informed about the importance of regular eye check-ups and proper use of spectacles for the correction of refractive error. As birth asphyxia is a major risk factor for cerebral palsy, it is emphasized that the prevention and treatment of perinatal asphyxia is essential for preventing the development of cerebral palsy. Multidisciplinary approach involving paediatrician, neurologists, ophthalmologists, counsellors and physiotherapist should be embarked upon in managing these children from the time of diagnosis. References 1. Ghasia F., et al. “Frequency and Severity of Visual Sensory and Motor Deficits in Children with Cerebral Palsy: Gross Motor Function Classification Scale”. Investigative Ophthalmology and Visual Science 49.2 (2008): 572. 2. Landau L and Berson D. “Cerebral Palsy and Mental Retardation: Ocular Findings”.Journal of Pediatric Ophthalmology and Strabismus 8.4 (1971): 245-8. 3. Johnston MV, Hoon AH, Jr. Cerebral palsy. Neuromolecular medicine. 2006;8(4):435-50. 4. El-Hawary GR, Shawky RM, El-Din AS. Ocular features in Egyptian genetically disabled children. Egypt J Med Hum Genet 2011;12:171- 81. 5. Rosenbaum P, Paneth N, Leviton A, Goldstein M, Bax M, Damiano D, Dan B, Jacobsson B. A report: the definition and classification of cerebral palsy April 2006. Dev Med Child Neurol Suppl. 2007 Feb 1;109:8-14. 6. Beckung E, Hagberg G, Uldall P, Cans C; Surveillance of Cerebral Palsy in Europe. Probability of walking in children with cerebral palsy in Europe. Pediatrics 2008;121:e187-92. 7. Pennefather PM and Tin W. “Ocular abnormalities associated with cerebral palsy after preterm birth”. Eye (Lond) 14 (2000):78-81. 8. Jacobson L, Ygge J, Flodmark O, Ek U. Visual and perceptual characteristics, ocular motility and strabismus in children with periventricular leukomalacia. Strabismus2002;10:179-83. 9. Schenk-Rootleib AJ, Van Nieuwenhuizen O, Schiemanck N, Van der Graaf Y, Willemse J. Impact of cerebral visual impairment on the everyday life of cerebral palsied children. Child Care Health Dev 1993;19:411-23. 10. Chitra S, Nandini M. Symposium on developmental and behaviour discussion. 2005:72:865. 11. Schachat WS, Wallace HM, Palmer M, Slater B. Ophthalmologic findings in children with cerebral palsy. Pediatrics 1957;19:623-8. 12. Marasini S, Paudel N, Adhikari P, Baba Shrestha J, Bowan MD. Ocular manifestations in children with cerebral palsy. Optometry and Vision Development. 2011 Sep 1;42(3):178. 13. Katoch S, Devi A, Kulkarni P. Ocular defects in cerebral palsy. Indian journal of ophthalmology. 2007 Mar 1;55(2):154. 14. Reena A, Lekshmy S, Lekshmi H, Bindu K. Ophthalmic Manifestations in Children with Delayed Milestones-A Clinical Study. 243 Retinoblastoma. 2009:264. 15. Johnston MV, Fatemi A, Wilson MA, Northington F. Treatment advances in neonatal neuroprotection and neurointensive care. Lancet Neurol. (2011) 10:372–82. 16. Sanderson TH, Reynolds CA, Kumar R, Przyklenk K, Huttemann M. Molecular mechanisms of ischemia-reperfusion injury in brain: pivotal role of the mitochondrial membrane potential in reactive oxygen species generation. Mol Neurobiol. (2013). 17. Hertz BG, Rosenberg J, Sjo O, Warburg M. Acuity card testing in patients with cerebral visual impairment. Dev Med Child Neurol. 1988; 30: 632-7. 18. Madhavi MR, Kesuraju V,Nagrale P, Poka A. Ocular morbidity among school aged children in Indian scenario. Int J Res Med Sc2015;3:1431- 4. 19. Solomon CB, Bindu NM, Raju KV, George M. Ocular Associations In Children With Developmental Delay. Kerala Journal of Ophthalmology. 2011 Dec;23:367-371. 20. Ozturk AT, Berk AT, Yaman A. Ocular disorders in children with spastic subtype of cerebral palsy. International journal of ophthalmology. 2013;6(2):204. 21. Govind A, Lamba PA. Visual disorders in cerebral palsy. Indian journal of ophthalmology. 1988 Apr 1;36(2):88. 22. Sheeladevi, Seelam, Nukella et al; Prevalence of refractive errors in children in India: a systematic review. Clin Exp Optom2018; 101: 495–503. 23. Njambi L, Kariuki M, Masinde S. Ocular findings in children attending occupational therapy clinic at Kenyatta National Hospital, Nairobi, Kenya. The Journal of Ophthalmology of Eastern, Central and Southern Africa. 2009;15(1). 24. Huo R, Burden SK, Hoyt CS, Good WV. Chronic cortical visual impairment in children: aetiology, prognosis, and associated neurological deficits. British Journal of Ophthalmology. 1999 Jun 1;83(6):670. 25. Elmenshawy AA, Ismael A, Elbehairy H, Kalifa NM, Fathy MA, Ahmed AM. Visual impairment in children with cerebral palsy. International Journal of Academic Research. 2010 Sep 1;2(5):67-71. Dr. Indu Dhiman, MS Assistant Professor, Department of Ophthalmology, Dr. RPGMC Kangra at Tanda (HP) Corresponding Author: Subspecialty - Neuro-Ophthalmology

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 62 63 An Overview of Optical Coherence Tomography Angiography Sanjeev Kumar Neiniwal, MD, DNB, MNAMS, Mansi Sonwar, MBBS, Khushbu Jindal, MS, Siddharth Maanju, MS Vitreo Retinal Services, Department of Ophthalmology, Sawai Man Singh Medical College & Hospital, Jaipur, Rajasthan India. Introduction Optical coherence tomography angiography (OCTA) is a new non-invasive imaging technique that employs motion contrast imaging to high-resolution volumetric blood flow information generating angiographic images in a matter of seconds. OCTA compares the decorrelation signal (differences in the backscattered OCT signal intensity or amplitude) between sequential OCT B-scans taken at precisely the same crosssection in order to construct a map of blood flow. Axial bulk motion from patient movement is eliminated so sites of motion between repeated OCT b-scans represent strictly erythrocyte movement in retinal blood vessels.[1] Optical coherence tomography angiography (OCTA) first became commercially available in 2014. This technology allowed for the visualization of retinal microvasculature in vivo. Prior to OCTA. Fluorescein angiography (FA) and indocyanine green angiography (ICGA) were the mainstay modalities for retinovascular visualization. These imaging modalities generated a 2-dimensional en face view of the retinal vasculature and did not allow for the individual visualization of retinal capillary plexuses. OCTA offered in vivo visualization of the retinal micro- vasculature in a depth-resolved fashion, without the need for time-consuming dye administration.[2] Prior to its commercial release, OCTA was available as a research tool. Investigational groups explored the utility of OCTA in a wide range of ocular pathologies including age related macular degeneration (AMD), diabetic retinopathy (DR), chroidal neovascular membrane, vascular occlusion, glaucoma and uveitis. Functioning Principles OCT-A technology uses laser light reflectance of the surface of moving red blood cells to accurately depict vessels through different segmented areas of the eye, thus eliminating the need for intravascular dyes. The OCT scan of a patient’s retina consists of multiple individual A-scans, which when compiled into a B-scan provides cross-sectional structural information. With OCT-A technology, the same tissue area is repeatedly imaged and differences are analysed between scans (over time), thus allowing one to detect zones containing high flow rates (i.e. with marked changes between scans) and zones with slower, or no flow at all, which will be similar among scans.[3] Light is emitted through either a spectral domain OCT (SDOCT), with a wavelength of near 800nm; or a swept-source OCT (SS-OCT), which utilizes a longer wavelength, close to 1050nm. Longer wavelengths have a deeper tissue penetrance, but a slightly lower axial resolution. OCT-A employs two methods for motion detection: amplitude decorrelation or phase variance. The former detects differences in amplitude between two different OCT B-scans. Phase variance is related to the emitted light wave properties, and the variation of phase when it intercepts moving objects. To improve visualization and reduce background noise from normal small eye movements, two averaging methods - split spectrum amplitude decorrelation technique and volume averaging - were developed. These OCT-A algorithms produce an image (3mm to 12mm) that is segmented, by standard, into four zones: the superficial retinal plexus, the deep retinal plexus, the outer retina and the choriocapillaris. Applied to the optic disc it includes its full depth. Currently, there are 4 main commercially available OCT-A devices:[4] • ZEISS AngioplexTM OCT angiographic imaging on the CIRRUSTM HD-OCT platform, with a scanning rate up to 68,000 A-scans per second and an improved tracking software known as FastTracTM. A three-dimensional image is obtained depicting erythrocyte flow as well as the microvasculature of the superficial, deep, and avascular layers of the retina. • Optovue AngioVue® (Optovue, Inc., Freemont, CA), which uses split-spectrum amplitude-decorrelation angiography Subspecialty - Retina

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 62 63 algorithm, which minimizes motion noise. This system also allows quantitative analysis, since it provides numerical data about flow area and flow density maps. • Topcon® uses a different algorithm, OCTA RatioAnalysis, which benefits from being paired with SD-OCT, and improves detection sensitivity of low blood flow and reduced motion artifacts without compromising axial resolution. Strengths of OCTA OCTA displays in vivo retinal vasculature in a depth-resolved fashion. Segmentation of volumetric data leads to identification of retinal capillary plexuses individually, providing detail and resolution similar to that of histologic studies. Further, OCTA provides improved visualization of the deep capillary plexus and choroid when compared to FA and ICGA.[8] OCTA does not utilize dye to visualize vessels which confers it with multiple advantages. First, OCTA generates high-contrast images that are not obscured by dye leakage from vessels, leading to more pronounced definition of retinal vasculature. Second, this dye free imaging modality does not expose patients to the risks associated with contrast dye, which range from mild allergic reactions to anaphylaxis. Patients that have relative contraindications to dye imaging, including those with renal failure or poor intravenous access, can undergo OCTA imaging without limitations. OCTA imaging is fast and thus useful for patients that require recurrent vascular imaging, such as those being treated with vascular endothelial growth factor. Interpretations To ensure correct interpretation, the three-dimensional quality of OCTA imaging must be respected. Viewing two-dimensional OCTA representations without simultaneously interacting with the three-dimensional dataset can confound interpretation. As a general rule, three images must be concurrently assessed for accurate OCTA interpretation: the en face OCTA image; • Heidelberg engineering® uses the active eye-tracking system (TruTrackTM) that assesses simultaneously fundus and OCT images acquisition in order to achieve a better signalto-noise ratio. Subspecialty - Retina

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 64 65 the corresponding B-scan with flow overlay and segmentation lines displayed; and the structural en face intensity image for the selected slab. Assessing all three image components at once reduces erroneous findings. • Inner Retinal Slab It extends from 3 µ below the internal limiting membrane to 15 µ below the inner plexiform layer. • Middle Retinal Slab It extends from 15 µ below the inner plexiform layer to 70 µm below the inner plexiform layer. Inner Retinal Slab Outer Retinal Slab Outer Retinal Choriocapillaris Complex Middle Retinal Slab • Outer Retinal Slab Extends from 70 µm below the inner plexiform layer to 30 µm below the retinal pigment epithelium (RPE) reference line. • Outer Retinal Choriocapillaris Complex Choriocapillaris extends from 30 µm below the retinal pigment epithelium (RPE) reference line to 60 µm below the RPE reference line. OCTA Scans of Normal Patient Subspecialty - Retina

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 64 65 Color Coded S- Superficial (red) D- Deep (green yellow) A- Avascular (blue) Optic Nerve Head Montage Step 1: Fundus photograph of AMD patient. Step 2: En face image showing full retinal depth, avascular slab and choriocapillaris. Step 3: Segmentation is accessed through out the slab to ensure accuracy. Step 4: B scan through le shows clear flow suggesting MNV. Step 5: En face intensity image for the choriocapillaris shows a strong signal. OCTA interpretation in patient with AMD Vascular Metrics These metrics aims to quantify vascular features like density and morphology[5] Subspecialty - Retina

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 66 67 • Vessel Area Density A unitless measure that reacts the proportion of the OCT angiogram that is occupied by vessels of all caliber. This is typically accomplished by first binarizing the image such that the area occupied by vessels is comprised of white pixels and the avascular area is comprised of black pixels. A proportion of the white pixels divided by the total pixels in the image provides a measure of vessel density. • Vessel Skeletal Density One limitation of vessel area density is the variability of vessel caliber among OCT angiograms in different eyes. For example, one eye may by chance have a greater number of larger vessels than another within a set window, thereby giving a false impression that it has increased density. Vessel skeletal density adjust for this variability by iteratively deleting outer pixels of each vessel such that each individual vessel, regardless of size, is represented by only a single line of pixels. OCT angiogram of a healthy eye (left) and an accompanying binary image of its vessel skeleton (right). • Vessel Diameter Index This value reflects the average vessel diameter within an OCT angiogram and is calculated by dividing vessel area density by vessel skeletal density. Spectral Domain and Swept Source OCTA The most widely available prototype OCTA system is the AngioVue software of the RTVue XR Avanti spectraldomain OCT (SD-OCT) (Optovue, Inc, Fremont, CA), which uses a split-spectrum amplitude decorrelation angiography (SSADA) algorithm. The device obtains volumetric scans of 304 × 304 A-scans at 70,000 A-scans per second in approximately 3.0 seconds. The software offers the option of 2 × 2 mm, 3 × 3 mm, 6 × 6 mm, and 8 × 8 mm OCT angiograms and automated segmentation of these full-thickness retinal scans into the “superficial” and “deep” inner retinal vascular plexuses, outer retina, and choriocapillaris. The OCT angiogram segmentation of the superficial inner retina contains a projection of the vasculature in the retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL). The deep inner retina OCT angiogram segmentation shows a composite of the vascular plexuses at the border of the inner plexiform layer (IPL) and inner nuclear layer (INL) and the border of the INL and outer plexiform layer (OPL). The OCTA prototype with the fastest acquisition rate was developed by the Massachusetts Institute of Technology using a swept-source OCT (SS-OCT) device (Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachussetts Institute of Technology, Cambridge, MA). This ultra-high-speed prototype employs a vertical cavity surface emitting laser (VCSEL) operating at 1060 nm wavelength which allows increased light penetration into pigmented tissues and improved choroidal blood flow visualization compared to the light source used in SD-OCT. The SS-OCTA system obtains scans of 500 × 500 A-scans at 400,000 A-scans per second in approximately 3.8 seconds. This ultra-high speed allows for imaging of wider fields of view. The prototype can be manipulated to obtain OCT angiograms up to 12 × 12 mm, however, it is most commonly used to create 3 × 3 mm and 6 × 6 mm OCT angiograms of great detail Fullthickness scans are manually segmented into the superficial (plexus at the RNFL), intermediate (plexus at the GCL), and deep (plexuses at IPL/INL and INL/OPL borders) inner retinal vascular plexuses, outer retina, choriocapillaris, and choroidal layers. Using this OCTA system, the choriocapillaris and choroidal vessels were described in normal eyes. Clinical Utility of OCTA OCTA of Diabetes OCTA provides high resolution images of the retinal capillary beds, and can identify early vascular changes associated with DR that FA missed. In fact, recent studies show OCTA can identify vascular changes in diabetic patients without signs of retinopathy.[6] These studies suggest the potential of OCTA as a screening tool for diabetic patients. Aside from its promise in identifying early changes in diabetic eyes, OCTA can be used as a follow-up tool for patients with DR. There are three main findings of particular relevance to clinical practice: foveal avascular zone (FAZ) enlargement, detection of microaneurysms, and vascular changes. • FAZ Enlargement Early FA studies show that FAZ area increases with DR severity. OCTA studies have replicated these findings in the full retinal layer, the superficial capillary plexus and the deep capillary plexus. Clinically, assessing FAZ enlargement over time can be a useful tool for following DR progression. Subspecialty - Retina

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 66 67 • Microaneurysms Microaneurysms (MA) are a landmark finding in DR and are associated with an increased risk of progression to advanced disease stages. Tough MA tracking has little utility in assessing treatment response in DME, the presence of increased microaneurysm and ischemia may mark areas at higher risk of DME recurrence. • Vascular Changes A negative association between vessel density and increasing DR severity at both the superficial and deep capillary plexuses has been repeatedly identified. OCTA is also useful in the clinical management of PDR. PDR is an advanced stage of DR that can lead to vision threatening complications such as hemorrahage and tractional retinal detachment. Neovascular changes associated with PDR can been visualized on OCTA. OCTA can identify neovascular growth and follow its regression in response to anti-VEGF treatment. OCTA of AMD and MNV Age-related macular degeneration (AMD) is characterized by drusen, pigmentary changes, and photoreceptor and RPE loss, called geographic atrophy (GA). Decreased foveolar choroidal blood flow is associated with AMD and increased drusen extent. Areas of impaired choriocapillaris flow typically extended beyond the borders of the GA. Eyes with dry AMD were shown to have a generalized decrease in choriocapillaris density, which was sometimes associated with drusen. Choroidal Neovascular Membrane Type 1 CNVM Type 2 CNVM Type 3 CNVM TYPE 1 CNVM: A well-defined neovascular network under the retinal pigment epithelium TYPE 2 CNVM: Detachment of retinal pigment epithelium with subretinal hyperreflective material and subretinal fluid TYPE 3 CNVM: A tuft-shaped, high-flow lesion in the inner retinal layers Subspecialty - Retina

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 68 69 OCTA of Vascular Occlusion The OCTA (BRVO) showed a large wedge-shaped area of capillary nonperfusion in the inferotemporal macula with clear delineation of the boundary of ischemia, and vascular abnormalities such as microaneurysms, telangiectasis and anastamoses. The BRAO demonstrates wedge-shaped areas of capillary nonperfusion that correlate to areas of abnormalities on the retinal thickness map. This illustrates the potential use of OCTA in pinpointing areas of ischemia and edema. The CRAO shows diffuse capillary nonperfusion in areas supplied by the central retinal artery as seen on the same-day FA. Flow is still seen in the major retinal vessels. Around the optic disc, there is an absence of blood flow in the superficial disc vasculature supplied by the central retinal artery but the lamina cribosa blood flow remains intact. The preservation of deep vasculature has been associated with better visual outcomes.[7] BRVO with Neovascularisation Central Serous Chorioretinopathy Overlap between findings in FA of a pigmented epithelium detachment (PED) and CNVM may lead to situation of misdiagnosis. Especially in suspicious cases of flat and irregular PEDs, OCT-A may be helpful in diagnosis and management of CNVM. Although some reports mention a decreased choriocapillaris blood flow[8], one should pay attention to signal strength in en face images before interpreting this as hypoperfusion. Macular Telangiectasia OCTA of Glaucoma OCTA is a useful tool for evaluating optic disc perfusion in glaucomatous eyes. The normally dense peripapillary microvascular network is attenuated in both the superficial disc vasculature and the deeper lamina cribosa. Averaging the decorrelation signal in OCT angiograms approximates the area of microvasculature and allows the user to calculate the flow index, which is decreased in eyes with glaucoma. The flow index has been shown to have both a very high sensitivity and specificity in differentiating glaucomatous eyes from normal eyes. OCTA identifies dilated, irregular telangiectatic vessels and sometimes choroidal communication. Since OCTA does not detect leakage OCT B scan may help stage and manage MacTel without using FA.[9] Subspecialty - Retina

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 68 69 Artifacts • Media Opacities - media opacities such as corneal scarring, cataracts, posterior capsular opacification, and vitreous floaters may lead to signal attenuation and shadowing artifact. • Projection Artifact - related to light that traverses blood vessels and is reflected back by deeper layers, which will appear in the final deep image with a similar vascular pattern as overlying superficial vessels. A) OCTA image without projection artifact removal, various large vessels seem to be connected with the neovascularization. B) After removal of the projection artifact, the actual size and the extent of the neovascularization can be assessed. • Segmentation Error - Automated segmentation of a structural abnormal retina. • Motion Artifact - Excessive motion of the eye can lead to motion artifacts as seen in the image Motion Artifact • Extravascular signal from exudative edema - Hyperreflective fluid, a form of exudate, is thought to be caused by suspended particles. OCT-A devices may capture the motion of these particles, leading to extravascular artifact. A) Color depth-encoded OCT angiogram of an eye with moderate non-proliferative diabetic retinopathy and exudative macular edema. The edema can be seen as green extravascular signal extending across the foveal avascular zone. (B-C) B-scans extending through two areas of the hyperreflective macular edema. Overlaying flow signal (red) over the structural scans illustrates both the motion of particles in the edema and red blood cells in the vessels. Subspecialty - Retina

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 70 71 Limitations of OCTA Beyond its many advantages OCTA has a number of limitations. As aforementioned, flow detection on OCTA requires scanning a single location multiple time. This increases imaging times, especially for larger scan areas. Newer devices with faster scanning speeds have shorter image acquisition times, but capturing large amounts of data at fast speeds translates into slower processing and saving times. Furthermore, device hardware and software are highly variable between OCTA manufacturers. Each device is programmed with a proprietary algorithm to detect flow. The difference between these algorithms is highly technical and beyond the scope of this discussion. However, clinicians must be aware that such differences exist, as they can affect imaging results. When possible, patients should be imaged on the same device to assure accurate comparison between visits. Moreover, image size can affect the degree of vascular detail captured.[10] The A-scan density for each scan size differs, affecting the visualization of fine vessels. Vessels that are clearly visualized on a 3×3 mm scan might not be as salient on a 6×6 mm scan, creating the illusion of vessel drop-out when the true difference lies in image resolution. Consistent imaging with the same device and scan size can improve vascular tracking overtime. Lastly, though dye-free OCTA imaging is safer for patients, it has some disadvantages. OCTA cannot visualize dye leakage, a common landmark of inflammatory vascular pathology and a sign of blood-retinal barrier breakdown. OCTA cannot provide information on transit time or vascular filling either. Moreover, ultra-wide field fundus photography allows FA to capture vascular detail in the retinal periphery. Tough newer OCTA devices have larger scan patterns available, the ability of OCTA to detect pathology in the retinal periphery, such as peripheral non-perfusion, remains limited. References 1. De Carlo et al. 1:5 A review of optical coherence tomography International Journal of Retina and Vitreous (2015) DOI 10.1186/ s40942-015-0005-8. 2. Spaide RF, Fujimoto JG, Waheed NK, Sadda SR, Staurenghi G. Optical coherence tomography angiography. Prog Retin Eye Res. 2018;64:1–55. 3. Ghazala D.O’Keefe et al. optical coherence tomography American Acacdemy of Opthalmology 2022. 4. Pichi F, Sarraf D, Arepalli S, et al. The application of optical coherencetomography angiography in uveitis and inflammatory eye diseases. ProgRetin Eye Res. 2017 Apr 29. 5. Kim AY, Chu Z, Shahidzadeh A, Wang RK, Puliafi to CA, Kashani AH.Quantifying microvascular density and morphology in diabeticretinopathy using spectral-domain optical coherence tomographyangiography. Invest Ophthalmol Vis Sci. 2016;57:OCT362–OCT370. 6. Sorour OA, Sabrosa AS, Yasin Alibhai A, et al. Optical coherence tomography angiography analysis of macular vessel density before and after anti-VEGF therapy in eyes with diabetic retinopathy. Int Ophthalmol. 2019;39:2361–71. 7. Wakabayashi T, Sato T, Hara-Ueno C, et al. Retinal Microvasculature and Visual Acuity in Eyes With Branch Retinal Vein Occlusion: Imaging Analysis by Optical Coherence Tomography Angiography. InvestigOpthalmology Vis Sci. 2017;58(4):2087. 8. Teussink MM, Breukink MB, van Grinsven MJJP, et al. OCT Angiography Compared to Fluorescein and Indocyanine Green Angiography in Chronic Central Serous Chorioretinopathy. Investig Opthalmology Vis Sci.2015;56(9):5229. 9. Zhang Q, Wang Rk, Chen C-L, Et Al. Swept Source Optical Coherence Tomography Angiography Of Neovascular Macular Telangiectasia Type 2.Retina. 2015;35(11):2285-2299. 10. Rabiolo A, Gelormini F, Marchese A, et al. Macular perfusion parameters in different angiocube sizes: does the size matter in quantitative optical coherence tomography angiography? Invest Ophthalmol Vis Sci.2018;59:231–7. Dr. Sanjeev Kumar Nainiwal, MD, DNB, MNAMS Senior Professor Ophthalmology, Sawai Man Singh Medical College & Hospital, Jaipur Rajasthan India. Corresponding Author: Subspecialty - Retina

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 70 71 Clinical Perspective: Low Dose Atropine for Myopia Control Rohit Saxena, MBBS, MD, PhD, Vinay Gupta, MS, PhD Scholar Dr R P Centre for Ophthalmic Sciences, AIIMS, New Delhi. Childhood myopia is an important public health problem in the world including in India with nearly 50% of the world’s population is expected to myopic and 10% having high myopia. Slowing or limiting the extent of myopia progression reduces the risk of the development of vision-threatening disease (such as retinal detachment and myopic maculopathy) as well as improving the quality of life. With the approval and availability of Low-dose atropine (0.01%) in India, this has emerged as the most accepted therapy for myopia control in recent years. Atropine eye drops work by blocking the action of acetylcholine, a neurotransmitter that is involved in controlling the size of the pupil and the shape of the eye’s lens. By blocking the action of acetylcholine, atropine can prevent the eye from elongating, which is a major contributor to the development and progression of myopia. The exact mechanism by which atropine works to control myopia is still not fully understood, but it is believed to involve the modulation of the eye’s growth factors and signalling pathways. The use of low dose atropine for myopia control involves careful consideration of several factors to ensure the safety and efficacy of treatment. Certain important considerations are age (reportedly most effective in younger patients aged 5 to 15 years); severity of myopia (myopic refractive error between -1D to -6D at the time of enrolment); refractive stability (patients with stable refractive errors may not benefit as much from low dose atropine treatment, documented myopia progression should be ≥ 0.5D/ year); ocular health (patients with certain ocular conditions, such as glaucoma or uveitis, may not be suitable candidates for low dose atropine treatment); compliance (low dose atropine treatment requires daily administration for at least 1 year, which may be challenging for some patients) and side effects (low dose atropine may cause side effects such as light sensitivity and blurred vision). In general, low dose atropine is recommended for children and adolescents with progressive myopia. The medication is typically prescribed in concentrations of 0.01% (received DCGI approval) or 0.05% (off-label), administered as eye drops once a day (usually at bedtime). Both concentrations have been shown to be effective in slowing the progression of myopia, but they have different side effect profiles. Atropine 0.01% is associated with fewer and less severe side effects compared to 0.05%. This concentration has been shown to be effective in reducing myopia progression by 50-60% with minimal impact on pupil size, accommodation, and near vision. Atropine 0.05%, on the other hand, has been shown to be more effective in reducing myopia progression, with studies reporting a reduction of up to 77%. However, this concentration is associated with greater side effects such as photophobia, blurred vision, and difficulty focusing on near objects. These side effects can impact compliance and reduce the quality of life for patients. Moreover this is still not approved in India and has to be especially compounded and dispensed. Patients must be informed about their off-label use and an informed consent should be taken. The choice between atropine 0.01% and 0.05% will depend on several factors, including the amount of myopia progression, patient history, and individual tolerance for side effects. In clinical practice, 0.01% concentration is commonly used for myopia control, as it has been shown to be effective in slowing the progression of myopia while minimizing the risk of side effects. The treatment is generally well-tolerated, with few side effects reported. However, some individuals may experience a temporary increase in light sensitivity, blurred vision and/ or decreased near vision; particularly in the first few weeks of treatment. These side effects are generally mild and temporary, but they can be concerning for some patients and may affect compliance with treatment. The management strategy includes assessment of ocular health and myopic refractive error (cycloplegic refraction) and its progression; communicating and educating parents/guardians (and patient) about associated risk of myopia; discussion of treatment option efficacy, risks, and additional correction benefits; performing baseline examinations and measurement of ocular biometric parameters and then prescribe low dose atropine and accordingly schedule next follow-up. The initial follow up can be planned as 2 weeks (to check for associated side effects, if any), 2 months (to check compliance) and then 6 monthly (for efficacy) post enrollment. The treatment efficacy can be analyzed in terms of change in myopic refractive error and (or) axial-length from baseline to last visit. The treatment can be tapered and stopped when either the desired effect is achieved or when myopia progression is not sufficiently controlled, in comparison to expected progression. Numerous studies conducted worldwide have shown good efficacy of low-dose atropine to prevent myopia progression in children. In India, a placebo-control randomized multicentric trial (I-ATOM study) reported 54% reduction in mean spherical Subspecialty - Refraction

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 72 73 equivalent progression and 21% reduction in mean axial length elongation in atropine-treatment group compared to placebo with no significant side effects at one year. Overall, the clinical perspective of using low-dose atropine for myopia control is positive. It represents a safe and effective treatment option for children with myopia who are at risk for developing high myopia, which can increase the risk of visionthreatening conditions. However, clinicians prescribing low dose atropine to prevent myopia progression should carefully monitor patients for both the desired effects and potential side effects of the medication. Regular follow-up visits and monitoring of visual acuity, refractive error, and ocular health are essential for ensuring the safety and effectiveness of treatment. In summary, low dose atropine is a promising treatment option for myopia control, but careful consideration of patient factors as well as proper monitoring is essential for successful clinical implementation. Prof. Rohit Saxena, MBBS, MD, PhD Dr. R. P. Centre for Ophthalmic Sciences, AIIMS, New Delhi, India. Corresponding Author: Subspecialty - Refraction

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 72 73 Small Incision Lenticule Extraction (SMILE) Surgery as an Effective Strategy to Treat Megalocornea: A Case Report Cyres Mehta, MBBS, MS, FAICO, FSVH, FASCRS, Keiki Mehta, MBBS, MS, DO, FAICO International Eye Centre, Mumbai, India. Abstract: Megalocornea is a developmental defect in which the entire anterior segment is enlarged bilaterally. Megalocornea is associated with Marfan syndrome and other ocular and systemic congenital defects. One may suppose that in situations of megalocornea, there may be abnormal collagen production, abnormal collagen tissue/ cross-linking, a risk of corneal ectasia, and the presence of secondary glaucoma or cataracts, which may serve as the factors for not considering refractory surgeries. We report a case of megalocornea that was successfully treated with small incision lenticule extraction (SMILE) surgery. The patient noticed considerable improvement and no further complications were observed during the follow-up. Keywords: Cataract, Glaucoma, Laser surgery, Megalocornea, SMILE, Case report Introduction Megalocornea is a developmental defect in which the entire anterior segment of the cornea enlarges bilaterally in a nonprogressive manner.[1] Astigmatism from an enlarged cornea can cause impaired vision, and the disorder is typically asymptomatic in children. Adults may develop premature cataracts, usually between the ages of 30 and 50 years.[2] Some individuals with congenital megalocornea may not have any symptoms; as a result, the diagnosis may not be discovered until difficulties develop. There is no cure or therapy for enlarged corneas seen in megalocornea because the underlying anatomical problem is irreversible. We report a case of megalocornea that was successfully treated with SMILE using the VisuMax (ZEISS AG, Jena, Germany). Case Description A 31-year-old male sought consultation for refractive surgery of his myopic status, in November 2018. At the time of examination, he had best-corrected visual acuity (BCVA) of 6/6 in his right eye with -2.50 D Sph and 6/6 in his left eye with-1.75 D sph/ -2.25 D cyl x 155o . IOP in right eye was 17 mm and in left eye was 16 mm. Further evaluation under slit lamp revealed that patient had bilateral megalocornea (wtw distance 14.8 mm), with a clear cornea and a pachymetry of 413 and 401 microns in the right and left eye, respectively. Anterior segments were deep, iris was normal in appearance and the lens also appeared normal. Pre-operative corneal topography showed a simulated keratometry reading of right eye- 40.73 D (8.29 mm) @177o /41.35 D (8.16 mm) @87o and left eye- 40.18 D (8.40 mm) @150o / 41.83 D (8.07 mm) @60o (Figure-1a, b). The patient wanted an improved quality of life by becoming spectacle free as he was a swimmer and a sportsman, hence was very keen on refractive surgery. The lack of evidence in the literature to support refractive surgery and the hazard of performing refractive surgery on a patient with megalocornea were explained to the patient. After obtaining appropriate informed consent, the patient was taken up for lenticule extraction procedure with SMILE on 06/11/2018. Figure 1: A and B: Preoperative computerized corneal topography of both eyes. C and D: Postoperative computerized corneal topography of both eyes. Subspecialty - Refraction

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 74 75 Surgical Procedure The VisuMax500kHz femtosecond laser system (Carl Zeiss Meditec, Jena, Germany) was used. The SMILE/lenticule extraction procedure was performed in the operating room in sterile conditions by an ophthalmic surgeon. Topical anesthesia was used with 3 instillations of 2 drops of proparacaine at 30second intervals followed by a drop of povidone-iodine 10% solution (Wokadine, Dr. Reddys Laboratories, Ltd India) in both eyes and scrubbing of the eyelids with the same solution. To keep the eye open and in position during the laser treatment, an eyelid speculum was utilized, and a curved interface was placed on the VisuMax femtosecond laser platform for Table 1: Treatment data for ReLEx SMILE. alignment with the corneal surface. The patient was instructed to gaze at the blinking green light to achieve optimal centration. The laser procedure began by applying suction and creating the posterior surface of the refractive lenticule, followed by the 90-degree side cut and cap cut. Next, the entry cut was made at 135 degrees, extending 3.5 mm in length. After the laser treatment, a SMILE dissector specially designed by GeuderGermany was used to dissect the stromal lenticule in two sweepsone superficial and one deep. Finally, the lenticule was removed using lenticule extraction microforceps (Indo-German). The treatment data for SMILE and the parameters for the procedure are mentioned in tables 1 and 2. Right Eye Left Eye Treatment pack Size S S Suction time 00:00:33 00:00:32 Cap Data Diameter 8.00 mm 7.70 mm Thickness 130 µm 120 µm Side cut angle 90o 90o Incision position 140o 135o Incision angle 43o 45o Incision width 3.00 mm 3.00 mm Lenticule Data Optical Zone 6.70 mm 6.50 mm Transition Zone 0.10 mm 0.10 mm Thickness Min 25 µm Max 83 µm Min 15 µm Max 96 µm Side cut angle 90o 90o Refractive Correction Sphere -2.75 D -2.25 D Cylinder -0.60 D -3.00 D Axis 60o 155o Expected Result Sphere 0.00 0.00 Cylinder 0.00 0.00 Axis 60 155 RST 260 µm 256 µm Subspecialty - Refraction

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 74 75 The patient was discharged with appropriate follow-up advice. He was followed up regularly. On 13/11/2018, his refraction was emmetropic. Slit lamp pictures 6 months after the SMILE procedure are presented in Figure-2. Nearly four years post refractive procedure, on 08/06/2022, he reported for a followup. He underwent repeat investigations. The patient continues to be emmetropic. Pachymetry of both eyes preoperatively using Optovue Parameter Lenticule Lenticule Side Cap Cap Side Scan mode Single - Single - Scan direction Spiral in - Spiral out - Energy (nJ) 28 28 28 28 Track distance ( µm) 4.0 4.0 4.0 4.0 Spot distance ( µm) 2.0 2.0 2.0 2.0 Table 2: Parameters for the procedure. showed cornea to be OD 473 µm and OS472 µm. The thinnest measurements were OD 409 µm and OS 395 µm (Figure-3) postoperatively. Post-operative corneal topography showed a simulated keratometry reading of right eye- 38.53 D (8.76 mm) @173o / 39.72 D (8.5 mm) @83o and left eye- 38.15 D (8.85 mm) @179o / 38.5 D (8.77 mm) @89o (Figure-1 c, d). Figure 2: A, B, C: Slit lamp pictures 6 months after SMILE. Figure 3: Pachymetry findings of both eyes. Subspecialty - Refraction

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 76 77 Discussion In megalocornea, two clinical presentation patterns were observed. Isolated megalocornea, known as primary megalocornea, lacks any accompanying ocular or systemic symptoms. Megalocornea, along with various ocular and systemic abnormalities, is the second most common clinical manifestation.[2] The case described is of primary or isolated type of megalocornea as the patient had no other associated features or presentations. SMILE is a variation of the refractive lenticule extraction technology and is a less invasive method of laser vision correction (LVC) for various ocular diseases.[3,4] SMILE was found to be superior to femtosecond-LASIK/LASIK in terms of preserving corneal biomechanical strength after surgery.[5] To treat megalocornea, ophthalmologists usually refuse to perform corneal refractive surgery. Due to the rarity of megalocornea, LASIK or PRK results may not be as predictable as they would be in eyes without this disorder. However, because megalocornea is linked to Marfan syndrome and other ocular and systemic congenital defects, one may suppose that in situations of megalocornea, there may be abnormal collagen production, abnormal collagen tissue/cross-linking, and a risk of corneal ectasia. Only after verifying that corneal stiffness and hysteresis were normal during testing with the Ocular Response Analyzer is PRK suggested as a therapy option.[6] To the best of our knowledge refractive surgeryhas not been tried as a treatment modality in managing patients with megalocornea. The presence of secondary glaucoma or cataract in these cases would also be a factor for not considering refractory surgeries in such cases, but our patient did not have any of these issues, and the LASIK treatment option was not opted for because of the flat cornea in this patient. Conclusion Considering the 4 days of pain and blurred vision, PRK was not the choice to treat this patient. Hence the SMILE surgery was considered, which proved to be beneficial as the patient noticed considerable improvement without any complications during follow-up. However, further efficacy may be established after SMILE surgery in clinical trials with larger samples of similar cases reported here. References 1. Mohan A, Kumar A, Sen P, Shah C, Sen A, Jain E. A rare case of unilateral anterior megalophthalmos with developmental glaucoma: Sequelae of megalocornea or a separate entity?. J Clin Ophthalmol Res 2020;8:72-4 2. Moshirfar M, Hastings J, Ronquillo Y. Megalocornea. [Updated 2022 Jul 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/ books/NBK554374/ 3. Ganesh S, Brar S, Arra RR. Refractive lenticule extraction small incision lenticule extraction: A new refractive surgery paradigm. Indian J Ophthalmol 2018;66(1):10-19 4. Moshirfar M, Somani SN, Patel BC. Small Incision Lenticule Extraction. [Updated 2022 Jun 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https:// www.ncbi.nlm.nih.gov/books/NBK549896/ 5. Guo H, Hosseini-Moghaddam SM, Hodge W. Corneal biomechanical properties after SMILE versus FLEX, LASIK, LASEK, or PRK: a systematic review and meta-analysis. BMC Ophthalmol 2019 Aug 1;19(1):167 6. Megalocornea [Internet]. CRSToday. [cited 2022Oct21]. Available from: https://crstoday.com/articles/2009-jun/crst0609_05-php/ Dr. Cyres Mehta, MBBS, MS, FAICO, FSVH, FASCRS Surgical Chief, International Eye Centre, Mumbai, India. Corresponding Author: Subspecialty - Refraction

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 76 77 Anterion – A multimodal Imaging Platform for Anterior Segment Yuganki Kush[1], MS, Pranita Sahay[2], MD, FRCS, FRCOphth, FICO, FAICO, DNB, Akanksha Koul[2], DNB FICO, Swati Singh[2], MS, Mahipal S Sachdev[2], MD 1. Fellow, Centre for Sight Eye Hospital, New Delhi. 2. Consultant, Centre for Sight Eye Hospital, New Delhi. Introduction In the current scenario, the clinical practice of ophthalmology has become highly dependent on various investigative modalities. For a comprehensive anterior segment evaluation, one would require multiple equipment for assessment of biometry, corneal pachymetry, corneal topography/tomography, anterior segment optical coherence tomography (ASOCT) and aberrometery. Access to a single equipment, that can combine all of this in a single platform will not only be cost effective but also save time for both the practitioner as well as the patient especially in heavy OPD practice. ANTERION (Heidelberg Engineering, Heidelberg, Germany), was commercially introduced in 2019 as a complete multimodal imaging platform for anterior segment surgeons.[1–5] It is a swept source OCT (SS-OCT) based anterior segment imaging system (including complete corneal tomography and imaging of anterior segment structures) with SS-OCT biometric device. It was designed to streamline the clinical workflow by providing an all in one solution for anterior segment evaluation including the patient’s ocular biometry, IOL power calculation, corneal tomography, ectasia risk score, corneal pachymetry with epithelial thickness map, aberrometry, anterior chamber metrics and 360 degree anterior chamber angle assessment.[1–5] In this article, we intend to highlight the applications and usefulness of Anterion in ophthalmic practice. Principle Anterion is a SS-OCT device that uses an infrared light source with wavelength of 1300 nm. The use of a longer wavelength makes it possible to image the anterior segment upto the posterior capsule of lens and a lateral scanning SS-OCT allows for cross-sectional imaging. Use of SS OCT has reduced the time of image acquisition as well as improved axial and lateral resolution and tissue penetration. It produces several A-Scans of the eye with an axial resolution of <10 µm, A-scan speed of 50 kHz, and a scan depth range of 32 mm for Axial length measurements. It acquires 65 radial B scans that generate the corneal topography data. Corneal diameter measurements are obtained via an en-face infrared camera. Anterion Applications The patients data captured on Anterion are categorised under four application that is the Cornea app, Cataract App, Metric app and Imaging App under which detailed patient information can be assessed. (Table 1-2) Cornea App Cataract App Metrics App Imaging App 1. OCT image 2. IR camera image 3. Anterior and posterior axial curvature maps 4. Anterior and posterior tangential curvature maps 5. Anterior and posterior elevation maps 6. Total corneal power map 7. Anterior and total corneal wavefront maps 8. Pachymetry map 9. Pupil diameter 10. Kappa angle 1. OCT image 2. IR camera image 3. Total corneal power map and parameters 4. Anterior axial curvature map and parameters 5. Total corneal wavefront 6. Central corneal thickness 7. Axial length 8. Aqueous depth 9. Lens thickness 10. Pupil diameter and kappa angle 11. White-to-white 12. Spheric IOL calculator 1. OCT image 2. IR camera image 3. ACA 500/750 4. SSA 500/750 5. AOD 6. 500/750 7. TISA 500/750 8. Lens thickness 9. Lens vault 10. Aqueous depth and anterior chamber volume 11. Angle-to-angle distance 12. Spur-to-spur distance 13. Central corneal thickness 1. OCT image 2. IR camera image Appliances

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 78 79 Cornea App Cataract App Metrics App Imaging App 11. White-to-white 12. Corneal vertex 13. Thinnest point 14. Ectasia view with SCORE analyzer 15. Epithelial thickness module 13. Toric IOL calculator 14. OKULIX ray tracing 15. IOL power prediction 14. White-to-white 15. Pupil diameter and kappa angle 16. Free hand measurements Parameter Measurement Range Axial Length 14.00 – 32.00 mm Central Corneal Thickness 300 – 1700 μm Anterior Chamber Depth 1.50 – 4.80 mm Lens Thickness 2.40 – 6.50 mm SimK Mean Anterior(3mm) 6.00 – 110.00 D K Mean Posterior(3mm) -14.80 – -0.70 D Astigmatism Anterior 0.00 – 15.50 D White-To-White 9.40 – 15.30 mm Pupil Diameter 0.20 – 14.10 mm Table 1: Ocular Parameters assessed on Anterion. Table 2: Measurement range for anterior segment parameters on Anterion. Figure 1: Anterion Corneal ectasia report in a case of keratoconus showing four maps on the left (anterior axial curvature map, pachymetry map, anterior and posterior elevation map) and detailed corneal metrics and SCORE report on the right. CORNEA APP 65 radial B-Scan images (256 A-scans per B-Scan) are acquired in less than one second using the ANTERION Cornea App to provide more than 16,000 data points for both the anterior and posterior corneal surface. All corneal maps are 8 mm in diameter and are generated from SS-OCT image data. These maps include: anterior and posterior axial curvature, tangential curvature and elevation maps, total corneal power map, anterior and total corneal wavefront and pachymetry maps.[2–4,6] (Figure-1) In addition, a detailed wavefront parameter analysis with aberration quantification is demonstrated for both anterior and total corneal wavefront. Also, it can provide corneal differential maps, progression analysis, Ectasia view with SCORE analyzer and epithelial thickness mapping that can help in better assessment of subclinical keratoconus patients. CATARACT APP It can measure the axial length (AL), lens thickness (LT), anterior chamber depth (ACD), central corneal thickness (CCT), anterior axial curvature and total corneal power.[5,7–12] Appliances

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 78 79 METRICS APP It can be used to calculate various indices and parameters for detailed analysis of anterior chamber angle.[1,13] (Figure-3) It gives quantitative assessment of anterior chamber volume, lens vault IMAGING APP It can take detailed image from the anterior surface of the cornea up to the posterior surface of the lens and provide corneal, scleral, Figure 2: Anterion Cataract spherical IOL calculation report for both eyes with detailed anterior segment parameters. Figure 3: Anterion metric report in a case of shallow anterior chamber showing narrow anterior chamber angle and high lens vault in the ASOCT image along with detailed anterior chamber, angle and lens metrics on the right. and lens thickness. It also allows for free-hand measurement of these parameters as well. In addition, it can provide a 360 degree graph of angle parameters. anterior chamber angle and, lens images to aid in diagnosis as well as patient education. (Figure-4) (Figure-2) In addition, it has an inbuilt spherical as well as toric IOL calculator. The toric IOL calculator takes the incision location, surgical induced astigmatism (SIA) into account and enables the surgeon to use the total corneal power as the corneal parameter for a more precise IOL power calculation. It also has an OKULIX ray tracing system for assessment of ocular aberrations. Appliances

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 80 81 Figure 4: Anterion imaging single report in a case of granular corneal dystrophy showing hyper-reflective lesion (white arrow) in superficial and deep cornea. Figure 5: Anterion cornea custom report showing the pachymetry, epithelial thickness and stromal thickness map along with detailed corneal metrics. Clinical Applications Role in Cataract Anterion can be put to use for ocular biometry and IOL power calculation in cataract patients.[5,7–12] It can also be used for toric IOL calculation. The availability of various IOL formulas like Barrett suite, Haigis, Holladay 1, SRK T, Hoffer Q and OKULIX ray tracing is an additional advantage in this system when dealing with challenging cases. The OKULIX can also predict the IOL power based on ray tracing technology in pseudophakic eye with the selected IOL model. As all the data is available in a single platform, the potential source for post-operative refractive surprise can also be easily identified. Anterion images can be also used to evaluate cases of lens subluxation (extent of subluxation) as well as to confirm IOL position after cataract surgery. Role in Corneal pathologies Comprehensive assessment of corneal ectasia cases can be easily performed in this machine with the help of topography and tomography maps.[2–4,6] The simultaneous availability of corneal thickness profile with stromal thickness and epithelial thickness mapping provides additional information that can be useful in cases of forme-fruste keratoconus.(Figure-5) Also, assessment of CCT changes over time can be done by trend analysis map. Corneal aberration profile measurement can also be done with this equipment. Appliances

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 80 81 Role in Refractive surgery Anterion Cornea app can be useful for screening patients prior to refractive surgery. It can be helpful in phakic IOL planning by providing data for WTW and ACD both of which are essential for lens sizing. In post-operative period it can be used for assessment of phakic IOL vault. (Figure-6) Role in Glaucoma It provides a detailed metrics of anterior chamber angle via a non-contact method. It is a useful tool for glaucoma experts and can be used for explaining the problem to patient of angle closure especially when planning for peripheral iridotomy. It can also assess the patency of laser peripheral iridotomy. Most studies have shown good repeatability of the automated measurements however limited literature exists on use of the machine in biometric analysis of pathological eyes such as corneal opacity or post refractive surgery corneas. Also limited normative data exists for the tomography parameters on a SSOCT based system as compared to a Placido disc or Scheimpflug imaging. Follow up and comparative topography scans of patient with keratoconus who have earlier been investigated using other systems of topography may be doubtful to note for any progression. To conclude, Anterion provides a multimodal imaging platform for anterior segment assessment and can be a useful tool in clinical practice. It averts the requirement to procure multiple equipment like biometer, topographer and OCT. Various studies have been done in the last few years to show agreement between the parameters obtained on Anterion, IOL master and Pentacam. Strong corelation have been noted in most studies suggesting reliable reporting by Anterion when compared to other gold standard methods of biometry and corneal tomography. References 1. Chan PP man, Lai G, Chiu V, Chong A, Yu M, Leung CK shun. Anterior chamber angle imaging with swept-source optical coherence tomography: comparison between CASIAII and ANTERION. Sci Rep. 2020;10(1). Figure 6: Anterion imaging Post-phakic IOL implantation showing a vault of 543 microns. 2. Tañá-Rivero P, Aguilar-Córcoles S, Ruiz-Mesa R, Montés-Micó R. Repeatability of whole-cornea measurements using a new sweptsource optical coherence tomographer. Eur J Ophthalmol. 2021;31(4). 3. Feng Y, Reinstein DZ, Nitter T, Archer TJ, McAlinden C, Chen X, et al. Heidelberg Anterion Swept-Source OCT Corneal Epithelial Thickness Mapping: Repeatability and Agreement With Optovue Avanti. Journal of Refractive Surgery. 2022;38(6). 4. Herber R, Lenk J, Pillunat LE, Raiskup F. Comparison of corneal tomography using a novel swept-source optical coherence tomographer and rotating Scheimpflug system in normal and keratoconus eyes: repeatability and agreement analysis. Eye and Vision. 2022;9(1). 5. Montés-Micó R, Pastor-Pascual F, Ruiz-Mesa R, Tañá-Rivero P. Ocular biometry with swept-source optical coherence tomography. Vol. 47, Journal of cataract and refractive surgery. 2021. 6. Kim KY, Lee S, Jeon YJ, Min JS. Anterior segment characteristics in normal and keratoconus eyes evaluated with a new type of swept-source optical coherence tomography. PLoS One. 2022;17(9 September). 7. Panda A, Nanda A, Sahoo K. Comparison of ocular biometry and refractive outcome between ANTERION and IOL Master 700. Indian J Ophthalmol. 2022;70(5). 8. Shetty N, Kaweri L, Koshy A, Shetty R, Nuijts RMMA, Sinha Roy A. Repeatability of biometry measured by three devices and its impact on predicted intraocular lens power. J Cataract Refract Surg. 2021;47(5). 9. Panthier C, Rouger H, Gozlan Y, Moran S, Gatinel D. Comparative analysis of 2 biometers using swept-source OCT technology. J Cataract Refract Surg. 2022;48(1). 10. Langenbucher A, Szentmáry N, Cayless A, Wendelstein J, Hoffmann P. Comparison of 2 modern swept-source optical biometers—IOLMaster 700 and Anterion. Graefe’s Archive for Clinical and Experimental Ophthalmology. 2022; 11. Lender R, Mirsky D, Greenberger R, Boim Z, Ben-Yaakov L, Kashtan C, et al. Evaluation of three biometric devices: ocular parameters and calculated intraocular lens power. Sci Rep. 2022;12(1). 12. Cheng SM, Li X, Zhang JS, Mei JQ, Shi GL, Lin J, et al. Comparison of Refractive Prediction Accuracy With Three Optical Devices. Journal of Refractive Surgery. 2023;39(1). 13. Meduri E, Gillmann K, Bravetti GE, Niegowski LJ, Mermoud A, Weinreb RN, et al. Iridocorneal Angle Assessment after Laser Iridotomy with Swept-source Optical Coherence Tomography. J Glaucoma. 2020;29(11). Dr. Pranita Sahay, MD, FRCS, FRCOphth, FICO, FAICO, DNB Associate Consultant-Cornea Cataract Refractive Surgery, Centre for Sight Eye Hospital, New Delhi. Corresponding Author: Appliances

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 82 83 Wnt Signaling Pathway in Ophthalmology: Emerging Paradigms Jatinder Bali[1], MS, MBA (Op Res.), Ojasvini Bali[2], MBBS 1. Municipal Corporation of Delhi. 2. Maulana Azad Medical College & LNJP group of Hospitals, Delhi. Abstract: Clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR Cas 9) is an exciting technology which has helped make genome editing faster, cheaper and more accurate compared to the other genome editing methods. The Wnt signaling pathway is conserved through species and has been implicated in many conditions. CRISPR Cas 9 interventions in the pathway may have a promising impact in diseases involving retinal neovascularization. Wnt signaling is involved in fetal tissue differentiation, angiogenesis, maintaining the blood-brain barrier, controlling the blood-retinal barrier and tissue regeneration. Wnt signaling pathway component mutations have been reported in neurovascular diseases including Norrie disease, familial exudative vitreoretinopathy, retinopathy of prematurity and Coats disease. This article briefly describes why Wnt signaling pathway is so important in translational research today and how it may impact clinical practice in the future. Keywords: CRISPR Cas 9, interventions, Wnt signaling pathway, genome editing, retinal neovascularization. What is Wnt Protein? Wnt gene plays a key role in growth and development in animals and has a highly conserved cysteine-knot motif structure studied in species from low invertebrates to vertebrates with homologousity of 27-83% in sequencing. The name Wnt is derived from Int and wingless gene. The Wnt gene was discovered by Nusse and Varmus in 1982. It was the site for integration of mouse mammary tumor virus and named the Int oncogene. It transmitted information regarding proliferation and differentiation between cells. Later a gene known as wingless gene in Drosophila was found to be orthologous with the gene from the mammary tumour. This was a multigene family coding for WNT protein which was the initiator of intracellular signaling for growth stimulation different dvelopment mechanisms like cell differentiation, migration and proliferation. Named after the promoter, it is called Wnt signaling pathway. Wnt gene family has 19 structurally related genes coding for cysteine-rich secreted glycoproteins which act as intracellular and extracellular signaling factors depending on the cell type and the receptors and/or co-receptors expressed.[1,2,3] Wnt proteins are secreted lipid-modified signaling glycoproteins 350-400 amino acids in length.[4] Palmitoylation of cysteines in highly conserved pattern of 23-24 cysteine residues permits the Wnt protein to bind to the membrane receptor by covalent attachment of fatty acids. Glycosylated Wnt proteins bind to a carbohydrate for proper secretion.[5] In Wnt signaling, these proteins activate different Wnt pathways via paracrine and autocrine routes as ligands. The protein structures are highly conserved across species of mice, humans, Xenopus, zebrafish, Drosophila and many others. What is the Wnt Signaling Pathway? The Wnt signaling pathway is a complex regulatory network characterized by three branches: canonical Wnt pathway, planar cell polarity (PCP) pathway and Wnt/Ca2+ pathway. They are activated by binding of a Wnt-protein ligand to a Frizzled family receptor (FZD).[6] This transmits a biological signal to the Dishevelled protein inside the cell. The canonical Wnt pathway regulates gene transcription. The noncanonical planar cell polarity pathway acts on the cytoskeleton and the shape of the cell. The noncanonical Wnt/calcium pathway controls calcium inside the cell.[2] PCP signalling controls locomotion inhibition by contact between neural cells which regulates the Rho GTPase activity locally. With RhoA activation Rac1 is inhibited at interface and collapse of protrusions with retraction of neural cells from each other takes place. We are primarily concerned about the first one ie Canonical Wnt pathway. It is also called WNT/β-Catenin Signaling pathway. It activates transcription of target genes by stabilizing β-catenin in the nucleus of the cell. β-Catenin is 80 kDa protein. β-Catenin in inactive state is bound in a β-Catenin destruction complex consisting of glycogen synthase kinase 3β (GSK3β), axin, adenomatous polyposis coli (APC) and casein kinase-1 (CK-1). β-catenin phosphorylated by the kinases leads to degradation by the ubiquitin proteasome system. When activated the receptor complex containing frizzled and LRP5/6 binds to WNT. This recruits disheveled (DVL) protein to the plasma membrane. When β-catenin destruction complex gets recruited to the What’s New

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 82 83 membrane, the phosphorylation of β-catenin is prevented in the cytoplasm leading to increased accumulation in the cytoplasm and translocation to the nucleus.[6] There it associates with transcription factors and stimulates transcription of WNT The planar cell polarity pathway or non-canonical Wnt signaling pathway controls cytoskeletal rearrangement by activating JNK (c-Jun N-terminal kinase). The Wnt/Ca2+ pathway affects cell adhesion and related gene expression by releasing intracellular Figure 1: Simplified Canonical (β-Catenin-Dependent) Wnt Signaling Pathway β-Catenin in inactive state is bound in a β-Catenin destruction complex consisting of glycogen synthase kinase 3β (GSK3β), axin, adenomatous polyposis coli (APC) and casein kinase-1 (CK-1). β-catenin phosphorylated by the kinases leads to degradation by the ubiquitin proteasome system. Wnt binding with FZD and LRP5/6 activates the cytosolic protein Dvl.Normally the β catenin is held in inhibition by core proteins glycogen synthase kinase 3β (GSK3β), axin, adenomatous polyposis coli (APC) and casein kinase-1 (CK-1). This inhibits destruction of β catenin. Accumulated stabilized β-catenin in lymphoid enhancer binding factor/T-cell specific transcription factor (LEF/TCF) transcription factors presence translocates latter into the nucleus to activate Wnt-responsive genes. Other signalling pathways are also involved. Figure 2: Planar Cell Polarity Pathway or Non-Canonical Wnt Signaling Pathway controls cytoskeletal rearrangement by activating JNK (c-Jun N-terminal kinase). The Wnt/Ca2+ pathway acts on Nuclear Factor of Activated T-cells (NFAT) gene family of transcription factors affecting cell adhesion, immune response and related gene expression by releasing intracellular Ca2+. Wnt/ Ca 2+ and Wnt/JNK pathways are independent of β-catenin-pathway. target genes. The canonical pathway affects tight junction formation and maintenance and hence the permeability in neovascularization.[7] Ca2+. The Wnt/Ca2+ pathway interacts with a typical Wnt/βcatenin signaling pathway.[6] Some overlap in the function cannot be ruled out. What’s New

DOS Times - Volume 29, Number 2, March-April 2023 www.dosonline.org/dos-times 84 85 Wnt Signalling in Clinical Ophthalmology Wnt signaling regulates multiple vascular beds in the eye with regression of hyaloid vessels and development of structured retinal vasculature layers. Wnt/β-catenin regulates differentiation of the ciliary margin and expansion of stem cells. Wnt activation by norrin:FZD4 binding affects retinal development. Aberrations in this pathway cause Wnt-associated vitreoretinopathies and are postulated to be a risk factor for developing ROP. Norrin-FZD4 signalling through the canonical and noncanonical pathways has been associated with development as well as maintenance of retinal vasculature in normal retinal angiogenesis. Increased Wnt ligands –3a, 5a, 7a and 10a were reported in animal models of pathologic angiogenesis (neovascularization) in exudative retinopathy and proliferative diabetic retinopathy.[8,9] Dysregulated angiogenesis lead to pathological vascular changes like breakdown of tight junctions, capillary drop-out, endothelial budding and neovascularization and primitive vascular trees development from vasculogenesis. Patients with gene mutations affecting Wnt signaling result in several pediatric vitreoretinopathies, such as Norrie disease, familial exudative vitreoretinopathy (FEVR), and pseudoglioma and osteoporosis syndrome.[9-13] Additionally, retinopathy of prematurity (ROP) has been associated with gene mutations affecting Wnt signaling.[10] Although Coats’ disease and persistent fetal vasculature (PFV) are generally unilateral and sporadic, Wnt-pathway mutations have been reported. E. coli-derived human Norrin protein Lys25-Ser133 with an N-terminal Met sequence is a 12.6 kDa disulfide-linked oligomer measured by its ability to activate Wnt induced TCF reporter activity in HEK293 human embryonic kidney cells expressing human Frizzled-4 and human LRP-5 produced by and available from Bio-Techne, Minneapolis, MN in United States. The ED50 for this effect is 30-150 ng/ml. Retinal vasculogenesis and angiogenesis are two separate processes with the former being associated with aggressive posterior retinopathy of prematurity. Vasculogenesis refers to de novo synthesis of blood vessels at the optic nerve head. Without norrin-FZD4 signaling normal vascularization does not proceed beyond vasculogenesis. In Norrie’s disease mutations either eliminate norrin protein translation or affect tertiary structure of the protein which interferes with norrin-FZD4 binding.[11] CRISPR/Cas9, a two-component system for targeted gene editing, consists of the single-effector Cas9 protein containing the endonuclease domains and a single guide RNA (sgRNA) carrying a scaffold sequence. Endonuclease domains- RuvC and HNH cleave the DNA strand non-complementary to the spacer sequence and the complementary strand respectively. sgRNA guides the CRISPR/Cas9 complex to its intended genomic location. The editing system then relies on either of two endogenous DNA repair pathways: non-homologous end-joining (NHEJ) or homology-directed repair (HDR) with the former creating random insertion and deletion of base pairs, or indels, at the cut site with frameshift mutations creating a premature stop codon and/or a non-functional polypeptide and the latter involving homologous region of the unedited DNA strand as a template to correct the damaged DNA. Homology directed repair holds clinical promise.[13] Conclusion The Wnt signaling pathway may be the next area of interventions in retinal neovascularization. Wnt signaling is involved in fetal tissue differentiation, angiogenesis, maintaining the bloodbrain barrier, controlling the blood-retinal barrier and tissue regeneration.[12] Wnt signaling pathway component mutations are implicated in neurovascular diseases including Norrie disease, familial exudative vitreoretinopathy, retinopathy of prematurity and Coats disease.[14] Norrie disease protein or X-linked exudative vitreoretinopathy 2 protein (EVR2) is a protein that is coded by Norrie Disease Protein gene on the X-chromosome in humans. Norrin activates Wnt pathway. Norrin binding to Frizzled 4-cell surface receptor (FZD4), low-density lipoprotein receptor-related protein-5 (LRP5) and tetraspanin family member-12 (TSPAN12) causes accumulation of β-catenin. β-catenin is a transcription factor affecting gene expression of genes promoting vascular and neural health.[10] Wnt actuators like Norrin, FZD4, LRP5, TSPAN12 are normally expressed in the adult retina. In acquired retinal vascular diseases tissue ischemia, vascular leakage, tissue edema and pathologic neovascularization were reported to improve with Norrin.[11] Norrin can promote repair and maintenance of retinal neural elements.[10,11] Exogenous Norrin protein can be used to treat both inherited and acquired retinal disease in the not so distant future. Authorship Contributions Concept: JB, OB, Design: JB, OB, Data Collection or Processing: JB, OB, Analysis or Interpretation: JB, OB, Literature Search: OB, Writing: JB, OB, Approval of manuscript: JB, OB. Ethics Ethics Committee Approval: The Ethics Committee approval was not applicable. Conflict of Interest No conflict of interest was declared by the authors. Financial Disclosure The authors declared that this study received no financial support. References 1. Tsukamoto AS, Grosschedl R, et al. Expression of the int-1 gene in transgenic mice is associated with mammary gland hyperplasia and adenocarcinomas in male and female mice. Cell. 1988; 55:619–625. 2. Tsaousi A, Mill C, George SJ. The Wnt pathways in vascular disease: lessons from vascular development. Curr Opin Lipidol. 2011;22(5):350-357. 3. Wang Y, Rattner A, Zhou Y, et al. Norrin/Frizzled4 signaling in retinal vascular development and blood brain barrier plasticity. Cell. 2012;151(6):1332-1344. 4. Slusarski DC, Yang-Snyder J, Busa WB, et al . Modulation of embryonic intracellular Ca2+ signaling by Wnt-5A. Dev Biol.1997;182:114-120. 5. Kühl M. The WNT/calcium pathway: biochemical mediators, tools and future requirements. Front Biosci. 2004;9:967-974. What’s New

www.dosonline.org/dos-times DOS Times - Volume 29, Number 2, March-April 2023 84 85 6. Wang Y, Rattner A, Zhou Y, et al. Norrin/Frizzled4 signaling in retinal vascular development and blood brain barrier plasticity. Cell. 2012;151(6):1332-1344. 7. Chen J, Stahl A, Krah NM, et al. Wnt signaling mediates pathological vascular growth in proliferative retinopathy. Circulation. 2011;124(17):1871-1881. 8. Wang Y, Rattner A, Zhou Y, et al. Norrin/Frizzled4 signaling in retinal vascular development and blood brain barrier plasticity. Cell. 2012;151(6):1332-1344. 9. Braunger BM, Tamm ER. The different functions of Norrin. Adv Exp Med Biol. 2012;723:679-683. 10. Ohlmann A, Tamm ER. Norrin: molecular and functional properties of an angiogenic and neuroprotective growth factor. Prog Retin Eye Res. 2012;31(3):243-257. 11. Ye X, Wang Y, Nathans J. The Norrin/Frizzled4 signaling pathway in retinal vascular development and disease. Trends Mol Med. 2010;16(9):417-425. 12. Thanos A, Todorich B, Trese MT. A novel approach to understanding pathogenesis and treatment of capillary dropout in retinal vascular diseases.Ophthalmic Surg Lasers Imaging Retina 2016; 47:288–292. Dr. Jatinder Bali, MS, MBA (Op Res.) Municipal Corporation of Delhi. Corresponding Author: 13. Cong L, Zhang F. Genome engineering using CRISPR-Cas9 system. Methods Mol Biol. 2015;1239:197–217. 14. Zhang C, Lai MB, Khandan L, et al. Norrin-induced Frizzled 4 endocytosis andendo-lysosomal trafficking control retinal angiogenesis and barrier function.Nat Commun 2017; 8:16-50. What’s New

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