Amblyopia

Posted by e-Medical PPT
Unilateral or less commonly, bilateral reduction  of best corrected visual  acuity that can not be attributed directly to the effect of any structural abnormality of the eye or the posterior visual pathway. Defect of central vision
Resulting from one of following:
Strabismus
Anisometropia or high bilateral refractive  error (Isoametropia)
Visual deprivation

Prevalence: 2%-4% in the North American population
Commonly unilateral
Nearly all amblyopic visual loss is preventable or reversible with timely detection and appropriate intervention.
Children with amblyopia or at risk for amblyopia should be identified at a young age when the prognosis for successful treatment is best.
Role of screening is important
Amblyopia is primarily a defect of central vision.
There is a critical period for sensitivity in developing amblyopia.
The time necessary  for amblyopia to occur during critical period is shorter for stimulus deprivation than for strabismus or anisometropia.

Neurophysiology:
Cells of the primary visual cortex can completely lose their innate ability or show significant  functional  deficiencies
Abnormalities also occur in neurons in the lateral geniculate body
Evidence concerning involvement at the retinal level remains inconclusive

Classification:
Strabismus Amblyopia
Anisometropia  Amblyopia
Amblyopia Due to bilateral high refractive error (isometropia)
Deprivation  Amblyopia

Diagnosis
Characteristics of vision alone cannot be used to reliably differentiated amblyopia from other form of visual loss.
The crowding phenomenon is typical for amblyopia but not uniformly demonstrable.
Afferent pupillary defect are Characteristic of optic nerve disease but occasiinally appear to be present with amblyopia
Multiple assessment using a variety of tests or performed on different occasions are sometime required to make a final judgment concerning the presence and severity of amblyopia.

Binocular  fixation pattern:
It is a test for estimating the relative level of vision in the tow eyes for children with strabismus who are under the age of about 3.
This test is quite sensitive for detecting amblyopia but results can be falsely positive.
Showing a strong preference when sision is equal or nearly equal in the tow eyes, particularly with small angle strabismic deviations.

The modified Snellen technique directly measures acuity in children 3-6 years old.
Often, however, only isolated letters can be used, which may lead to under estimated amblyopia visual loss.
Croding bar may help alleviate this problem.

Treatment
Treatment of amblyopia  involves the following steps:
Eliminating (if possible) any obstacle to vision such as a cataract
Correcting refractive error
Forcing use of the poorer eye by limiting use of the better eye.

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