This involves showing pairs of images to an infant and judging which of the pair the infant is looking at. If the infant consistently prefers to Objective Forced-Choice Preferential-Looking (FPL) look at one image in preference to the other, we can conclude that the infant sees the difference between the images. Infants will perform this task very well from birth. Hence we can even measure the vision of newborns.
Objective Forced-Choice Preferential-Looking (FPL)
Log MAR Chart
Lea Chart
Chart
VA Test
• Be tested @ Dist. and near, monocular and binocular, w/ and w/o correction •In the following order OD, OS, General comments & suggestions •In the following order OD, OS, OU • Pt is not squinting + untested eye be occluded • Pt has memorized the test letters, reverse reading / use another chart
General comments & suggestions • Encourage pt to guess at letters rather than skip over them • Binocular VA is often better than monocular VA
General comments (interpretation) Acuity w/ current (habitual) correction is used to: • Identify the possibility of uncorrected refractive error • Confirm a pt’s complaint of blurred vision • Provide a basis of comparison of the habitual Rx to the result of the subjective refraction
General comments (interpretation) Comparison of dist. and near VA can be used to: • Suggest the type of refractive error – myopia, hyperopia, or astigmatism • Suggest the impact of presbyopia on near vision Pinhole VA can be used as a supplemental test, reduction in VA is due to optical or organic causes
Addition Visual impairment is considered as 20/40 or worse in each eye. Low vision is defined as visual acuity of less than 6 /18 (20 /60), but equal to or better than 3 /60 (20 /400), or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction.
Addition Legal blindness Visual acuity of 20/400 or worse in the better eye with corrective lenses or Visual field restriction to 10 degrees diameter or less (tunnel vision) in the better eye. Note that the definition of legal blindness differs from country to country and that the criteria listed above are for the WHO.
The End