Amblyopia (Lazy Eye)

Amblyopia, commonly known as lazy eye, is a condition where the vision in one eye is reduced despite the eye being structurally normal. It occurs when the brain, during critical early visual development (typically from birth to age 7–8), receives a blurred or misaligned image from one eye and progressively reduces its reliance on that eye's signals. Over time, the brain 'switches off' the affected eye, leading to permanently reduced vision if left untreated.

Amblyopia develops when one eye transmits a significantly blurrier or more misaligned image to the brain than the other. Common causes include: (1) Strabismus — misaligned eyes, where the brain ignores the misaligned eye to avoid double vision; (2) Refractive error — especially when one eye has a much stronger prescription than the other (anisometropia); (3) Visual obstruction — such as congenital cataract, corneal scar, or ptosis (drooping eyelid) that blocks the visual axis; (4) Deprivation — when something physically blocks clear vision from reaching the retina.

Amblyopia affects approximately 2–3% of the UK population. It is one of the most common causes of vision loss in children. Early diagnosis and treatment, particularly before age 7–8, offer the best chance of restoring normal vision.

The visual system develops rapidly during early childhood, with the critical period for visual development extending to approximately age 7–8. During this time, the brain is highly 'plastic' — it can relearn to use the amblyopic eye if the stimulus is corrected and the eye is encouraged to see clearly. Once this critical period closes, the brain's visual pathways become more fixed, and the potential for improvement diminishes significantly. Treatment after age 10–12 is substantially less effective. Therefore, early detection and treatment are crucial.

Diagnosis begins with a comprehensive eye examination, including assessment of visual acuity in each eye separately (to detect if one eye has reduced vision), measurement of any eye misalignment, evaluation of refractive error, and assessment of the optics of the eye (ensuring there are no cataracts or other obstructions). In young children who cannot verbally report vision, special testing techniques such as cover testing, forced-choice preferential looking tests, and optokinetic drum assessments may be used. Imaging such as optical coherence tomography (OCT) may be performed to assess retinal health.