The Express Revision Series Ophthalmology

THE EXPRESS REVISION SERIES

OPHTHALMOLOGY

Applied Anatomy & Physiology
For Post Basic

OCULAR
SEGMENTS

by MaLINDA KAUR

"Life goes by in the blink of an eye and in the blink of an eye everything can change"

TABLE OF CONTENTS

Introduction 02
Anterior Segment 09
Posterior Segment 19
Express Revision 28

INTRODUCTION

Formed from nervous tissues

Derivation of eyeball structures

Eye and its associated structures

Located in orbital cavity with bony orbit

Wall of eyeball consisting three layers
Interior structures of eyeball

Blood and nerve supply to various structures of eye
Major arterial circle of iris and choriocapillaries

Arterial blood supply to various structures of eye
Blood supply to various structures of eye

Venous drainage of eye

ANTERIOR SEGMENT

1. Anterior segment of eyes includes:
i. Interior of eyeball: Anterior cavity – anterior chamber (between cornea and iris) and posterior
chamber (between iris and lens); aqueous humor
ii. Layers of eyeball – fibrous & vascular

2. Interior of eyeball: anterior cavity
i. Cornea
ii. Iris
iii. Lens
iv. Aqueous humor

3. Layers of eyeball:
i. Fibrous
ii. Vascular

2.1 CORNEA
Structure
1. Lines anterior 1/6 of eye
2. Transparent, avascular, no pigment
3. Photosensitive
4. Curved
5. 5 layers:
i. Outer (epithelium) -1 layer: nonkeratinized stratified epithelium acts as barrier
ii. Middle (connective) - 1 layer: dense connective of Bowman’s + 1 layer: Descemet’s

membrane + 1 layer: Stroma
iii. Inner (endothelium) - 1 layer: simple squamous epithelium maintains transparency and

partial dehydration

Function
Refract light onto retina

2.2 IRIS
Structure
1. Rainbow, colored portion of eyeball
2. Suspended between cornea and lens, surround pupil (hole at centre of iris)
3. Attached to ciliary process
4. Consist of melanocytes (black-green-blue); circular and radial smooth muscle
5. 6 layers:
i. anterior limiting layer – connective tissue above stroma
ii. stroma – connective tissue with various cells & blood vessels
iii. circular muscle – sphincter pupillae, contract pupil
iv. radial muscle – dilator pupillae, dilate pupil
v. anterior epithelium – non-pigmented
vi. posterior epithelium – pigmented

Function
Regulate amount of light entering eyeball through pupil

2.3 LENS
Structure
1. Transparent biconvex body bathed in aqueous humor
2. Posteriorly contact vitreous body, anteriorly contact posterior border of iris
3. Held in position by zonular fibers or suspensory ligament
4. Encapsulated by a clear connective tissue
5. Anterior: simple cuboidal epithelium
6. Posterior: no epithelium
7. Lateral at equator region: columnar epithelium mitotically active; at equatorial bow region: it

undergo further differentiation (elongate to form fiber cells), increase in intracellular protein
(crystallins) and loss of organelles
8. 3 layers:
i. epithelium
ii. cortex
iii. nucleus

Terminal differentiation of epithelial cells eventually form fiber layers of cortex and nucleus.
Crystallins arranged like an onion within lens cells, transparent and lacks blood vessels - serves

as refractive media. Lens lacks vascularity or innervation thus a constant flow of aqueous
humor vital for removal of waste and delivery of nutrients.

Function
Focus image on retina to facilitate clear vision

2.4 AQUEOUS HUMOUR
Structure
1. Transparent serous fluid (H2O 98%, electrolytes, protein)
2. Derived from plasma within fenestrated capillaries of ciliary processes
3. Secreted into posterior chamber
4. Posterior chamber → pupil → anterior chamber → scleral venous sinus / canal of Schlemm

(reabsorbed)
5. Aqueous humor completely replaced every 90 min, amount of secretion balances rate of

reabsorption

The flow of aqueous humour

Function
1. Nourishes avascular cornea and lens
2. Maintain shape of anterior eye

3.1 FIBROUS LAYER
Structure
1. Outer tough layer
2. Consists of anterior 1/6 transparent cornea and posterior 5/6 opaque sclera
3. At sclero-corneal junction, there is an opening: scleral venous sinus (canal of Schlemm)

3.11 SCLERA
Structure
1. ‘White eye’
2. 3 layers of dense connective tissue:
i. episclera - vascularized
ii. sclera proper - avascularized
iii. lamina fusca - pigmented
Function
1. Shape eyeball - makes more rigid
2. Protect interior eyeball
3. Attachment site for extrinsic eye muscles

3.2 VASCULAR LAYER
Structure
1. Vascularized middle layer
2. Also known as uvea / uveal tract
3. Consists of posterior 5/6 choroid and anterior ciliary body and iris

3.21 CHOROID
Structure
1. Highly vascularized
2. Lines internal surface of sclera and posterior surface of retina
3. Contain melanocytes – dark brown melanin pigment
4. 3 layers of loose connective tissue:
i. Bruch’s membrane – innermost layer that attached to retina
ii. stroma / vascular – middle layer contained large blood vessels, choriocapillaries supplying

retina, melanocytes, macrophages
iii. suprachoroid – outer membrane that contain interconnected fibers connecting choroid to

sclera

Function
Melanin absorbs stray light rays preventing reflection and scattering of light within eyeball to
produce sharp and clear image on retina

3.22 CILIARY BODY
Structure
1. In anterior portion of vascular tunic, choroid becomes ciliary body
2. Extend from ora serata (jagged retina anterior margin) to posterior sclero-corneal junction

(limbus)
3. Anterior ciliary body: pars plicata (ciliary process), non pigmented epithelium protrusions at

posterior to iris; contain blood capillaries and zonular fibers (suspensory ligaments) that
attached to lens
4. Posterior ciliary body: pars plana a flat, avascular and very pigmented epithelial surface at
ora serrata; contain melanocytes – dark brown melanin pigment
5. Besides vessels and epithelial, consist of ciliary muscle (circular smooth muscle)

6. 5 layers:
i. internal limiting membrane – innermost connective tissue
ii. non-pigmented epithelium – pars plicata, posterior to iris and cornea
iii. pigmented epithelium – pars plana, below sclera
iv. stroma – connective tissue with various cells and blood vessels
v. supraciliary lamina – posteriorly connected to suprachoroidal (below sclera), anteriorly

connected to anterior limiting membrane of iris

Function
1. Contraction and relaxation of ciliary muscle changes tightness of zonular fibers, which alters

shape of lens, adapting to near (accommodation) and far vision
2. Ciliary processes / pars plicata (epithelial) secrete aqueous humor

POSTERIOR SEGMENT

1. Posterior segment of eyes includes:
i. Interior of eyeball: Posterior cavity – vitreous chamber (between lens and retina); vitreous
body; optic disc and nerve; hyaloid canal
ii. Layers of eyeball – fibrous, vascular and nerve

2. Interior of eyeball: posterior cavity
i. Retina (fundus)
ii. Optic disc and nerve
iii. Hyaloid canal
iv. Vitreous body

3. Layers of eyeball:
i. Fibrous
ii. Vascular
iii. Nerve

2.1 RETINA
Structure
1. Third / inner layer of eye
2. Lines posterior ¾ of eye
3. Beginning of visual pathway
4. 2 layers:
i. pigmented (outer) – melanin-containing epithelial cells located between choroid + neural;

absorb stray light as choroid; no photoreceptor
ii. neural / sensory (inner) – multilayered outgrowth of brain; process visual data before send

nerve impulses into axons that form optic nerve

Jagged anterior margin of retina: ora serrata. From ora serrata to posterior iris: lined with
pigmented epithelium only

4.2 Multi neural layer:
i. photoreceptor cell layer: below pigmented layer; ependymal cell containing rods (night vision:

black, white and gray) + cones (day + color vision: blue, red and green);
ii. bipolar cell layer: 1st order neuron; contain horizontal cell + amacrine cell (lateral neural circuit)
iii. ganglion cell layer: 2nd order neuron (largest neuron of retina); separated by inner + outer

synaptic layer; most axons form optic nerve; some are photoreceptors contain sensory
pigment: melanopsin



In outer segment contain

disc of visual pigments

that absorb light. Old

discs (bleached) are

phagocytized by

pigmented epithelium

and replaced with new

ones from basal layer of

outer segment (50% of

bleached rhodopsin

regenerated in 5 min;

photopsin in 1.5min.

In exact center of retina posterior portion: macula lutea, a small flat yellow spot. In center of
macula lutea contains fovea centralis, a small depression contain only cones (rods are more to
periphery of retina) – area of highest visual acuity / sharpness of vision. Moving head and eyes
to place image right on fovea centralis in bright (cones); gaze head & eyes slightly to side to view

faint image in dark (rodes).

At fovea centralis, bipolar + ganglion cells include blood vessels are displaced laterally to
maximize amount of light falling onto exposed photoreceptor (cones)

Function
1. Receive light and convert into receptor potential + nerve impulse (sensory transduction)
2. Output to brain via axons of ganglion cells, which form optic nerve (CN II)
i. photoreceptor cell layer: initiate transduction; transmit impulse (graded potential: local) to

bipolar cell
ii. bipolar cell layer: transmit impulse (graded potential: local) to ganglion cell; horizontal cell +

amacrine cell transmit impulse laterally to enhance image perception (contrasts, edges)
iii. ganglion cell layer: most transmit impulse (action potential: systemic) to optic nerve; some

detect light intensity not visual images

2.2 OPTIC DISC AND NERVE
Structure
i. Optic disc: head of optic nerve; blind spot (no photoreceptor)
ii. Optic nerve: bundle of ganglionic cells (CNII); extends from optic disc to optic chiasma, tract

and radiation; bundled together with central retinal artery (supply anterior retina) and vein
(drain from retina via optic disc)

Function
1. Optic disc: or optic nerve head; site where optic nerve exits eyeball; carries 1–1.2 million

afferent optic nerve fibres towards brain; at centre has optic cup: blind spot
2. Optic nerve: transmits visual impulses to brain:
i. image perception: brightness, color and contrast (visual acuity)
ii. neurological reflexes: light reflex (constriction of pupils in bright light) and accommodation

reflex (lens adjusted more spherical to near vision)

2.3 HYALOID CANAL
Structure
1. A narrow channel that is inconspicuous in adults (in fetus occupied by hyaloid artery)
2. Runs through vitreous body from optic disc to posterior lens

Function
1. In fetus, hyaloid canal contains a prolongation of central retinal artery called hyaloid artery

which supplies blood to developing lens
2. After birth, hyaloid canal contains lymph to facilitate changes in volume of lens during

accommodation (compression of hyaloid canal to allow lens expansion in maintaining
intraocular pressure)

2.4 VITREOUS BODY
Structure
1. Also known as vitreous humor
2. Within the vitreous chamber
3. Lines 4/5 of eyeball
4. Transparent jellylike substance
5. Consists of water 98%, fiber collagen, hyaluronic acid (mucopolysaccharide), phagocytic cells
6. Does not undergo constant replacement unlike aqueous humor

Intraocular pressure produced mainly by aqueous humor and partly vitreous body (16mmHg) to
maintain shape of eye

Function
1. Body of eye – hold retina against choroid, provide even surface to retina for reception of

clear image
2. Transmit light
3. Remove debris, keep eyes clear from vitreal floaters (shadows)

EXPRESS REVISION

1. State the physiology of following structures.

2. Describe the gross anatomical structures of anterior segment.
3. Describe the anatomical structures of posterior segment.
4. Describe the wall of eyeball.
5. Describe the layers of retina and relate to the pathophysiology of retinal detachment.
6. Explain the layers of lens and relate to the pathophysiology of cataract.
7. Describe the pathological changes occur in persons with short-sightedness and long-

sightedness.
8. Explain the flow of aqueous humour and relate to the pathophysiology of glaucoma.
9. Describe on fovea centralis and relate on its significance in obtaining a sharp visual acuity during

bright.
10. Describe on blind spot and relate on how we missed seeing some of the images even though

nearby.
11. How would you view clearly a faint image in the dark?
12. Why did we sometimes capture a photograph of persons with red eyes?