Amblyopia: the critical period, patching and atropine

What it is

Amblyopia is reduced best-corrected vision in one eye, sometimes both, caused by abnormal visual experience while the visual system is developing. The brain favours the eye with the clearer image and the other eye's pathway fails to mature. Causes are strabismus, a large or unequal refractive error, and deprivation (cataract, a ptosis covering the pupil). It is the commonest cause of visual loss in one eye in children and is largely preventable with early screening.

Key facts

• Types: strabismic, refractive (anisometropic or bilateral high error) and deprivation, the most severe.
• Diagnosis: reduced best-corrected acuity, or a difference of two lines or more between the eyes, with no structural disease explaining it.
• The younger the child, the better the response; treatment works best before about 7 years.
• Treating the cause comes first: glasses alone improve many cases.

Step by step

1. Correct the refractive error with the full cycloplegic prescription and treat any cataract or ptosis.
2. Mild to moderate amblyopia: patching of the better eye or atropine penalisation (blurring the better eye).
3. Severe amblyopia: patching.
4. Colombian guideline: patch at least 2 hours a day if mild to moderate, 6 hours a day if severe; under 1 year, no more than half the waking hours.
5. Atropine penalisation two consecutive days a week, not in children under 3 years.
6. First review 4 to 6 weeks after starting, then every 2 to 3 months; taper treatment rather than stopping it abruptly.

In clinical practice

• Patching too long in a young child can make the good eye amblyopic, which is why the hours are limited.
• Adherence is the main problem: explain to the family that the patch is the treatment, not the glasses alone.
• Strabismic amblyopia is treated to improve vision before any squint surgery.

Next step / Initial management

• Suspected amblyopia (reduced acuity, a difference between the eyes, strabismus): refer to paediatric ophthalmology or optometry for cycloplegic refraction and an eye exam.
• If there is no response after 12 weeks, review adherence, age, severity and cause before stopping.
• After treatment: review every six months for the first year, then yearly, because amblyopia can recur.
• Deprivation causes (cataract, ptosis over the pupil) in infants: urgent referral.

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Elsewhere in DurgiPedia

• The visual pathway, pupillary reflexes and eye movements

Connections

← All of ophthalmology

Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once.

Sources: Guía de práctica clínica para la prevención, la detección temprana, el diagnóstico, el tratamiento y el seguimiento de la ambliopía en menores de 18 años (Guía No. 48) (Ministerio de Salud y Protección Social de Colombia, 2016); Amblyopia (StatPearls Publishing (NCBI Bookshelf), 2024).

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