Binocular Vision, Strabismus and Amblyopia
What this domain tests
Binocular vision questions test sensorimotor assessment, diagnosis of strabismus and amblyopia, and evidence-based treatment. You need to distinguish comitant from incomitant deviations and interpret accommodation.
Assessment
- Cover test and alternate cover test; prism neutralisation quantifies the deviation.
- Hirschberg and Krimsky tests estimate the angle when cover testing is impossible.
- Worth 4-dot, stereopsis and Maddox rod assess fusion and suppression.
- AC/A ratio is normally about 4-6 Δ/D; use the gradient method or calculated method.
Amblyopia and strabismus
- Amblyopia types: strabismic, anisometropic, deprivation; treat with refractive correction first, then occlusion or atropine penalisation.
- Accommodative esotropia: hyperopic correction; high AC/A may need a bifocal add.
- Intermittent exotropia: review, over-minus cautiously, refer if deteriorating.
Worked example
A 4-year-old has 3Δ esotropia at distance and 12Δ at near with +3.00 DS cycloplegic refraction. Reasoning: high AC/A accommodative esotropia. Prescribe the full hyperopic correction, add a bifocal if near alignment remains poor, and monitor amblyopia and stereoacuity.
Traps
Skipping cycloplegic refraction in a child; prescribing prism without sensorimotor assessment; missing anisometropic amblyopia in a straight-eyed child; treating a microtropia as a simple phoria.