Amblyopia

1. Amblyopia Presented by AmlanChakma B. Optometry, 5th semester Assam down town University

2. Amblyopia • Definition:- Amblyopia is the unilateral, or rarely bilateral, decrease in the best corrected visual acuity caused by form vision deprivation and/or abnormal binocular interaction, for which there is no identifiable pathology of the eye or visual pathway.

3. Classification of amblyopia 1. Strabismic amblyopia 2. Stimulus deprivation amblyopia 3. Anisometropic amblyopia 4.Meridional amblyopia 5. Isoametropic amblyopia 6. Amblyopia secondary to nystagmus 7. Idiopathic amblyopia

4. 1. Strabismic amblyopia:- The term strabismic amblyopia is used for the amblyopia seen in those patients with unilateral constant squint who strongly favour one eye for fixation 2. Stimulus deprivation amblyopia or amblyopia of disuse:- It results from vision deprivation. It may be unilateral or bilateral and typically caused by opacities in the media or ptosis that covers the pupil 3. Anisometropic amblyopia:- The term anisometropic amblyopia refers to the amblyopia occurring in an eye having higher degree of refractive error than the fellow eye 4. Meridional amblyopia:- The result of uncorrected astigmatism where one or both eyes are predominantly astigmatic 5. Isometric amblyopia:- It is bilateral amblyopia occurring in children with bilateral uncorrected high refractive error 6. Amblyopia secondary to nystagmus:- Bilateral amblyopia may occur secondary to Nystagmus 7. Idiopathic amblyopia:- It refers to unilateral amblyopia in apparently normal patients with negative history for strabismus and in the absence of other amblyogenic factors

5. Pathophysiology of amblyopia • Pathophysiology of amblyopia can be discussed under following headings: • Amblyogenic factors • Role of retina in the development of amblyopia • Active cortical inhibition

6. 1. Amblyogenic factors • Deprivation of form vision • Light deprivation • Abnormal binocular interaction

7. Deprivation of form vision • Monocular deprivation of form vision during the critical period of visual development results in amblyopia of the deprived eye • Binocular deprivation of form vision during the critical period of visual development results in amblyopia of the deprived eye b. Light deprivation:- It works as an amblyogenic factor in children with unilateral as well as bilateral complete cataracts c. Abnormal binocular interaction:- It plays a role of amblyogenic factor in children with strabismic, anisometripoa, and unilateral stimulus deprivation amblyopia

8. 2. Role of retina in development of amblyopia • There is some evidence that the retina itself is abnormal in amblyopia • Whether retinal abnormality is the effect or cause of amblyopia is debatable • It is widely believed and proved experimentally that there is a decreased sensitivity of foveal cones in amblyopia. However, reduction of foveal cones and retinal sensitivity is much less than the reduction in visual acuity • Electroretinography is found to be normal in amblyopic eyes. It, therefore, is improbable that a functional defect of foveal cones would be responsible for reduced visual acuity • It is believed that reduced inputs from the rods and cones in the affected eye cause certain neurophysiology changes, transmitted aberrantly to the CNS which triggers the onset of amblyopia

9. 3. Active cortical inhibition The role of active cortical inhibition of evidenced by following studies • Physiologic evidence • Pharmacological evidence

10. Diagnosis and evaluation • Evaluation of visual acuity • Neutral density filter test • Test for crowding phenomenon • Thorough ocular examination including fundus examination • Refraction • Evaluation of central versus eccentric fixation • Tests for other sensory anomalies

11. Management of amblyopia • Prevention and early detection • Treatment of amblyopia

12. 1. Prevention and early detection • Screening eye examination: I-ARM • Bruckerreflex test • Cataract can either block the red reflect light to give a white reflex • Anisometropia will result in an unequal red reflex • Strabismus will cause a brighter red reflex in the deviated eye, and the corneal light reflex will be decentered • Note: The key signs of a normal exam is symmetry

13. 2. Treatment of amblyopia Goal of amblyopia treatment is to maximize and potentially normalise visual acuity Strategies to treat amblyopia include: a. Elimination of the cause of visual deprivation and provision of clear retinal image b. Correction of ocular dominance

14. a. Elimination of cause of visual deprivation and Provision of clear retinal image • Media clearance • Correction of refractive error and spectacle adaptation b. Correction of ocular dominance • Occlusion therapy • Penalization • Pleoptics • Active stimulation therapy

15. Problems in amblyopia treatment • Problem in applying the occlude • Problem of parental corporation • Complications of occlusion • Recurrence of amblyopia

16. Prognosis • Younger the child better the prognosis • Amblyopia due to deprivation carries the poorest prognosis • Strabismic amblyopia has the best prognosis • Presence of eccentric fixation worsens the prognosis • Prognosis is better, when treated with total and full time occlusion than when treated with penalization or other methods

17. Refereces • Theory and practice of squint and orthoptics written by A.K.Khurana • Kanski’ clinical ophthalmology • www.google.com

18. Thank you