Amblyopia 2

Question 1

What is amblyopia

Answer 1

Amblyopia is a defective visual acuity in both or one eyes which persists after correction of the refractive error And removal of any pathological obstacle to vision

Question 2

What are the types of amblyopia

Answer 2

Stimulus deprivation - it affects one or both eyes ,
Can be virtually complete when little or no light enters the eye and no image is formed as in ptosis covering the pupil or it can be partial - allowing some passage of light e.g. a corneal scar

Other conditions that may result in this type of amblyopia- congential cataract, vitreous opacity

Strabismic amblyopia -
Consequence of unilateral or constant or near constant strabismus
It occurs mainly in esotropia - because most exotropia remain intermittent during childhood

Anisometropic amblyopia

• significant difference in the refraction of the two eyes such that one eye receives a clearer image for all distances
• the refractive error can be predominantly spherical or predominantly astigmatic

Meridiononal amblyopia - this occurs when their is moderate or high degree of uncorrected astigmatism in one or both eyes - the risk is increased if the astigmatism is oblique

Idiopathic amblyopia - not known cause

Ametropic - it is bilateral and occurs when their is a high degree of of refractive error in each eye

It occurs in association with high bilateral hypermeteopia in excess of 6DS

Question 3

What two factors are involved in the production of amblyopia

Answer 3

• form vision and abnormal binocular interaction

Deprivation of form vision- when no stimulus reaches the fovea or more commonly partial -when their is a degraded image

Abnormal binocular interaction - involved in all types of unilateral amblyopia but not in bilateral amblyopia provided each eye is affected to the same extent - it occurs when incompatible images are formed on the fovea

In stimulus deprivation amblyopia- competition is between the normal image and the white noise or degraded image formed in the affected eye

In strabismic amblyopia - competition results from visual confusion in which images of different objects stimulate the fovea and are seen superimposed

Anisometropic amblyopia - competition occurs when a defocused or distorted image of the fixation object is superimposed on the image projected from the normal fovea

Neurones from the two eyes are thought to compete for complete control over cortical connenections during the developmental period - those from the better eye gain control at the expense of neurones from the affected eye