deprivation as one eye constantly receives a blurred image. It is frequently associated with microstrabismus and may coexist with strabismic amblyopia. Relatively mild degrees of hyperopic or astigmatic anisometropia (1-2 D) can induce mild amblyopia. Mild Myopic anisometropia (<-3D) usually does not cause amblyopia, but unilateral high myopia (-6D) often results in severe amblyopic visual loss. iv)
Meridional amblyopia: It results from form vision deprivation in one meridian. It can be unilateral or bilateral and is caused by uncorrected astigmatism. The degree of cylindrical ametropia necessary to produce meridional amblyopia is not known but most ophthalmologists recommend correction of greater than 2.00 D of cylinder
v)
Ametropic amblyopia: Bilateral amblyopia, which is the result of a high degree of uncorrected bilateral refractive error. Hyperopia exceeding about 5D and myopia in excess of 10D carry a risk of inducing bilateral amblyopia.
vi)
Occlusion amblyopia: It is a form of deprivation amblyopia caused by excessive therapeutic patching.
Investigations for Amblyopia Case history: Early-onset, unilateral, constant strabismus with long duration without treatment predisposes to strabismic amblyopia. Congenital ocular pathology such as cataract and ptosis predispose to stimulus deprivation amblyopia. Visual acuity: If possible it is better to use a linear test type. The patient may demonstrate the crowding phenomenon where reduced visual acuity is detected on linear testing, despite better visual acuity on single optotype. This is due to additional stimulation from contours of adjacent letters in a linear test type which produces confusion. Refraction: Anisometropia, high astigmatism and bilateral high refractive errors are aetiological factors. Cover test: There may be unilateral constant strabismus. By observing fixatation and reaction to occlusion and estimate of visual acuity can be obtained. Visuscope: Fixation may be eccentric or wandering, in a parafoveal, parama,ular or peripheral retinal area. Neutral density: This test makes use of the fact that amblyopic eyes perform relatively well under condition of low illumination. The visual acuity, when tested with the filter, is not significantly reduced in thIq amblyopic eye when compared with visual acuity of the normal eye. This test differentiates between amblyopia and reduced visual acuity due to organic defects, as organic amblyopia will have further reduction in visual acuity under poor illumination. Ocular Examination: Detailed ocular examination including fundus examination should be done to exclude any ocular pathology that may reduce vision. Visual Acuity Assessment in Children