Amblyopia (Lazy Eye)

What is Amblyopia (Lazy Eye)?

Amblyopia, commonly called lazy eye, occurs when vision in one eye does not develop normally during childhood. The brain begins to favour the stronger eye and suppresses signals from the weaker one. It is the most common cause of preventable visual impairment in children, affecting approximately 2–3% of the population. Early diagnosis and treatment — before the visual system matures around age 7–8 — gives the best chance of full recovery.

Symptoms

• Reduced vision in one eye (often discovered at school screening)
• An eye that appears to turn in, out, or upward (may indicate an underlying squint)
• Squinting, closing one eye in bright light, or tilting the head
• Difficulty with depth perception
• Poor performance on vision tests that test each eye separately

Causes

• Strabismus (squint) — the most common cause; the brain ignores the misaligned eye to avoid double vision
• Refractive error difference between the two eyes (anisometropia) — one eye is significantly more short- or long-sighted
• Deprivation amblyopia — a condition blocking vision in one eye, such as a congenital cataract or severe ptosis

Diagnosis

A full orthoptic and ophthalmic examination, including refraction (measuring glasses prescription) and vision testing of each eye separately. Younger children are assessed using age-appropriate vision tests, prism cover tests and cycloplegic refraction.

Treatment

Treatment depends on the underlying cause and must begin as early as possible. Glasses are prescribed to correct any refractive error. Patching the stronger eye (occlusion therapy) forces the brain to use the amblyopic eye and rebuild the neural connections. Atropine penalisation (blurring the better eye with drops) is an alternative to patching. Where a structural cause is present (cataract, ptosis, squint), surgery may be required first.