Amblyopia

Question 1

Amblyopia

Answer 1

partial reversible loss of vision in one or both eyes for which no cause can be found by physical examination of the eye i.e. there is absence of any organic disease of ocular media, retina and visual pathway

pathogenesis
- due to amblyogenic factors during critical period of visual development (birth to 6-7 years age)
- this period has development of the visual pathway and brain learns to interpret the signals
- if one or both eyes are not functioning normally it could lead to incomplete development of the vision
- leading to amblyopia
- most sensitive period: first 6 months. does not develop after 6-7 years

amblyogenic factors
- visual deprivation (anisometropia)
- light deprivation (congenital cataract)
- abnormal binocular interaction (strabismus)

Question 2

amblyopia types and c/f

Answer 2

types
1) strabismic amblyopia
- prolonged uniocular suppression in children with unilateral constant squint
- most common cause
- common with esotropia than exotropia (fovea of deviated eye has to compete with the strong temporal hemifield (nasal retina) of the normal eye) leads to foveal imbalance

2) stimulus deprivation amblyopia (amblyopia ex anopsia)
- one eye is totally excluded from seeing early in life eg. cong / traumatic cataract, complete ptosis and dense central corneal opacity

3) anisometropic amblyopia
- eye having higher degree of refractive error than the other eye.
- anisohypermetropic > anisomyopic
- even 1-2 d of anisohypermetropia can cause amblyopia

4) isometropic amblyopia
- b/l amblyopia with b/l uncorrected high refractive error
- b/l hyperopia >+5D
- b/l myopia >-8D
mild degree

5) meridional amblyopia
- children with uncorrected astigmatic refractive error.
- selective amblyopia for a specific visual meridian
- >1.5D u/l
->2.5D b/l

c/f
poor hand eye coordination, poor depth perception, head tilt, partial shutting of eye

signs
1) visual acuity - reduced
- recognition acuity more affected than resolution
- mild - VA 20/25 to 20/60
- moderate - VA 20/70 to 20/100
- severe - VA 20/200 or worse

2) effect of neutral density filter
- VA improves by one or two lines and decreases in pt with organic lesions

3) crowding phenomenon
- VA less with multiple letter charts (snellens) than with single (optotype)

4) fixation pattern - may be central or eccentric

5) colour vision - normal.
affected in deep amblyopia with vision below 6/36

Question 3

treatment

Answer 3

as early as possible.
works best with <3 years of age

1) occlusion therapy
occlusion of normal eye to force use of amblyopic eye
(opacity should be removed. refractive error should be corrected)

methods : adhesive patch, gauze pad and tape, doynes rubber occluder (on spectacle lens), opaque contact lens, ground glass occluder

types of occlusion
1) full time occulsion
- all waking hours but one a day
- observed at interval of 1 week to avoid occulsion amblyopia in the sound eye

occlusion should be done according to the age
for 2 year old : 2:1
2 days of normal eye and 1 day of amblyopic eye

2) part time occlusion
- 4-6 hours per day

duration should be till VA develops fully or if there is no further improvement after 3 months

maintenance occlusion (2hrs a day) should be done till amblyogenic age (8 years)

2) penalization ie blurring of vision of normal eye
- atropine penalization or optical penalization (over plus glasses)

3) pleoptic exercises - past

4) pharmacological manipulation - adjunct
- levodopa / carbidopa

5) perceptual learning - adjunct

6) computerized active vision therapy (computerized home vision therapy)
2x for 30 minutes