Basics of amblyopia Definition, Classification, Clinical features, Pathogenesis in brief, with T...

Basics of amblyopia

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Basics of amblyopia Definition, Classification, Clinical features, Pathogenesis in brief, with Treatment by Mind Map: Basics of amblyopia  Definition, Classification, Clinical features, Pathogenesis in brief, with Treatment

1. What do you understand by amblyopia ?

1.1. Amblyopia is a condition with unilateral or bilateral decrease of visual functions, caused by form vision deprivation and/or abnormal binocular interaction, that cannot be explained by a disorder of ocular media or visual pathways itself and in appropriate cases it is reversible by therapeutic measures.

2. What is the prevalence of amblyopia ?

2.1. Prevalence worldwide :1-5 %, India :1.1 %

3. What do you understand by critical period ?

3.1. It is the period of time during visual development when anatomy and physiology of the visual system are pliable and beyond which reversal of amblyopia can not be attained or attained only partially. Critical period : 0-7 yrs Most sensitive : 0 – 3 yrs

4. How to classify amblyopia ?

4.1. 1:Strabismic amblyopia (most common), 2:Anisometropic amblyopia (2 nd most common), 3:Form deprivation a- Stimulus amblyopia b-Ametropic amblyopia ,4: Organic amblyopia , 5: Toxic amblyopia , 6:Nystagmus related

5. Clinical features to look for in amblyopia

5.1. VISUAL ACUITY TESTING: 1. Bruckner's Test : symmetrical/ asymmetrical ( High refractive error ,media opacity) , 2: Fixation Pattern: Fixes follows light/ CSM, 3:Fixation preference :Non preferred eye is more amblyopic ,4: age appropriate VA testing

5.1.1. FIxation preference grading A: Spontaneous alteration between 2 eyes, B (Holds well) : Fixation of non preferred eye for >/= 3 secs. through a blink , smooth pursuits before switching to preferred eye , C: (Holds momentarily) fixation held with NP eye for 1- <3 secs, D: (Does not hold well) refixation to preferred eye immediately

5.1.2. Visual acuity difference A difference in BCVA of of two Snellen lines (1 octave difference) between two eyes is considered significant If both eyes are affected, difference from age related norm is taken

5.2. Look for crowding phenomena

5.2.1. Abnormal contour interaction Single optotypes are seen better than when presented in a row Single optotype acuity improves more rapidly than line acuity on treatment Both single letter and line acuity should approach each other on treatment or else there is always risk of recurrence of amblyopia

5.3. Other features

5.3.1. Decreased Vernier acuity and grating acuity Decreased stereoacuity Decreased brightness perception Increased perception and reaction times

5.4. Other examination points

5.4.1. Presence of strabismus ,Refractive error, fundus examination to rule out organic amblyopia

6. Diagnosis of amblyopia

6.1. Unilateral amblyopia

6.1.1. 1. Asymmetric occlusion to monocular fixation , 2:Failure to initiate or maintain fixation, 3: Interocular differences of 2 or more on PFL , 4: Interocular differences of 2 or more lines on BCVA testing

6.2. Bilateral amblyopia

6.2.1. 3-4 years BCVA less than 20/50 , 4-5 years BCVA less than 20/40 , >5 years BCVA less than 20/30

7. Important considerations in Pathogenesis of amblyopia

7.1. Normal visual experience is necessary for cortical visual development

7.2. It was Hubel and Wiesel who showed the axons of relay cells in the lateral geniculate nucleus terminate in layer IV of the primate primary visual cortex (area 17) usually segregate over the first 3 weeks of life to form the ocular dominance columns in which the inputs from the two eyes alternate equally.

7.3. If one eye was closed at birth, its ocular dominance bands became very narrow and those from the fellow eye expand. This enlargement of the LGN cell bodies has more extensive axonal arborizations in their enlarged ocular dominance bands in the visual cortex.

7.4. The shrinkage of parvocellular cell bodies in the LGN occurs as monocular closure prevents binocular cooperation and the cortical axonal arborizations of parvocellular cells related to both eyes make fewer connections and are smaller than normal.

7.5. The maturity of the ODC continues till the age of 36 months postnatally and during this maturation process visual experience from the two eyes must be matched. This process makes the cortical circuits immune to any visual experiences usually after 10 years of age

8. Management

8.1. Glasses

8.2. SURGERY - according to cause

8.2.1. Squint

8.2.2. Peadiatric cataract

8.2.3. Ptosis

8.2.4. Corneal surgery

8.3. Patching

8.3.1. How and which eye ? The sound / good eye is patched and the duration of patching is according to the degree of amblyopia Mild - 2 hrs/ day, Moderate- 4 hrs/day Severe - 6 hrs/day - Any duration of patching must be combined with 2 hours of near vision tasks. can the child take break during patching ?

8.4. Pharmacological penalization

8.4.1. what is the drug ? Atropine 1% eye drops how frequent we should use ? when it is preferred?

8.5. COAT therapy

8.5.1. what is coat therapy ? Combined occlusion therapy and atropine penalization what are the Indications of COAT therapy ? How successful is this ?

8.6. Bangerter filters

8.7. Advanced treatments

8.7.1. Vision therapy

8.7.2. Binocular therapy I - pad therapy Dichoptic therapy

8.7.3. Liquid crystal glasses

8.8. Parent counselling

8.8.1. how important is this ? 1. Explaining the condition and the treatment options Monitoring the child activities at home. to take care of compliance Regular follow up- importance enforcement of near vision tasks daily

8.9. Follow up every 2-3 months

8.9.1. Detailed examination + BCVA + compliance If BCVA in both eyes is unchanged - then increase patching hours ( 2 to 6 ) If BCVA in Amblyopic eye is increased- Then continue same treatment if BCVA of Amblyopic eye alone is decreased - then suspect subtle macular abnormalities, or other anterior visual pathway disorders. If BCVA of Sound eye is decreased - ? Reverse Amblyopia - Retest and re check VA - stop amblyopia therapy . What if the child is with subnormal improvement despite good complaince? Complete evluation + look for organic causes

8.9.2. How to keep a track on follow up ? AMBLYOPIA PROGRESS CARD