AKT · Ophthalmology/Neuro-ophthalmology

Strabismus & amblyopia

Ocular misalignment (concomitant childhood vs incomitant/paralytic) ± amblyopia of the deviating eye

Overview

Strabismus (squint) is misalignment of the visual axes. Concomitant strabismus (constant angle in all directions, usually childhood esotropia) is commonest; incomitant/paralytic strabismus follows a cranial-nerve palsy. Amblyopia is reduced vision in a structurally normal eye from abnormal visual development (strabismic, refractive/anisometropic or deprivation) during the critical period — reversible ONLY if treated early. The screen and cover test exist to catch it.

Recognise

Visible turn — esotropia (inward), exotropia (outward); abnormal/asymmetric corneal light reflex (Hirschberg)
Positive cover test: covering the fixing eye makes the deviating eye move to take up fixation
Amblyopia: reduced acuity in one eye with loss of stereopsis; paralytic squint → diplopia, abnormal head posture

Red flags

NEW squint or one with LEUKOCORIA / absent red reflex → exclude retinoblastoma and congenital cataract — urgent referral
Acute incomitant (paralytic) squint, esp. CN6 → think raised ICP (false-localising); CN3 with a fixed dilated pupil → aneurysm

Differentials & how to tell them apart

Pseudostrabismusprominent epicanthic folds simulate a squint but the corneal light reflexes are SYMMETRIC and the cover test is normal

Cranial nerve palsy (incomitant)the angle varies with gaze direction; consider a neurological cause in a new adult squint

Retinoblastoma / congenital cataractleukocoria / absent red reflex — the must-not-miss cause of a new squint

Investigations

Corneal light reflex (Hirschberg) + cover/uncover test; visual acuity each eye; cycloplegic refraction; dilated fundoscopy and red reflex (exclude retinoblastoma/cataract). Orthoptic assessment.

Management

Treat amblyopia — correct refractive error then patch/penalise the better eye (orthoptics/paediatric ophthalmology)

1Refer to orthoptics/paediatric ophthalmology. Correct refractive error with glasses first; then treat amblyopia by occlusion (patching) or atropine penalisation of the BETTER eye to force fixation by the amblyopic eye.Gate: Amblyopia is reversible ONLY within the critical period (the younger, the better) — and a new squint with leukocoria/absent red reflex must be referred urgently to exclude retinoblastoma/congenital cataract before treating as a simple squint
2Residual misalignment after amblyopia is treated → extraocular muscle surgery (alignment/cosmesis). Paralytic squint → treat the neurological cause.

Refractive correction (glasses) — treat any underlying refractive error first — may correct accommodative esotropia

Occlusion (patching) or atropine penalisation of the BETTER eye — forces use of the amblyopic eye during the critical period

Key points

Corneal light reflex + cover test detect it; symmetric reflexes = pseudostrabismus (reassure). Amblyopia is only treatable if caught early — which is why children are screened. A new squint with a white pupil is retinoblastoma until proven otherwise. (Cross-references child health.)

Monitor & prognosis

Acuity in the amblyopic eye and patching compliance; alignment.

Excellent if amblyopia is treated early; permanent visual loss if missed beyond the critical period.

Source: RCOphth/orthoptics; cross-ref child_health