Amblyopia (Lazy Eye)
Amblyopia is a neurodevelopmental disorder characterized by decreased visual acuity in one or both eyes due to abnormal visual development during the critical period (birth to 7–9 years of age). It occurs due to inadequate stimulation of the visual pathway, leading to reduced visual function that is not correctable by refractive means alone and has no structural abnormality of the eye.
Causes (Etiology)
Amblyopia can be classified based on the underlying cause:
- Strabismic Amblyopia – Caused by constant or intermittent strabismus (ocular misalignment), leading to suppression of the deviated eye.
- Refractive Amblyopia – Due to uncorrected refractive errors:
- Anisometropic Amblyopia – Significant difference in refractive power between the two eyes.
- Isometropic Amblyopia – High but equal refractive errors in both eyes.
- Deprivation Amblyopia – Caused by conditions that obstruct visual input during early life (e.g., congenital cataract, ptosis, corneal opacity).
- Meridional Amblyopia – Due to high uncorrected astigmatism leading to blurred vision in specific meridians.
- Organic Amblyopia – Rare form due to retinal or optic nerve pathology, though structural changes are often subtle.
Signs and Symptoms
- Reduced visual acuity in one or both eyes (usually unilateral).
- Poor depth perception (stereopsis).
- Abnormal fixation preference (in cases of strabismic amblyopia).
- Absence of structural abnormalities on fundoscopic examination.
- Visual improvement not proportional to refractive correction.
Investigations
- Visual Acuity Testing – Using Snellen's chart, HOTV chart, or Lea symbols in children.
- Cycloplegic Refraction – To detect anisometropia or high refractive errors.
- Ocular Alignment Tests – Cover-uncover test for detecting strabismus.
- Fundus Examination – To rule out organic causes.
- Optical Coherence Tomography (OCT) – May help in detecting subtle structural abnormalities.
Management
1. Correction of Underlying Cause
- Refractive Correction – Spectacles or contact lenses for anisometropia or high refractive errors.
- Surgical Correction – For conditions like congenital cataracts, ptosis, or significant strabismus.
2. Occlusion Therapy (Mainstay of treatment)
- Patching of the better-seeing eye to stimulate the amblyopic eye (full-time or part-time occlusion based on severity).
- Duration: 2–6 hours per day depending on age and severity.
3. Penalization Therapy
- Atropine 1% drops in the better eye to blur vision and force the amblyopic eye to function (used in mild to moderate cases).
4. Vision Therapy
- Activities like reading, drawing, and playing video games with the amblyopic eye to enhance visual function.
5. Monitoring and Follow-up
- Regular follow-ups to assess compliance and response to treatment.
- Treatment is more effective before the age of 7–9 years.
Prognosis
- Good if detected and treated early (before age 7).
- Poor if untreated or diagnosed late, as visual development is nearly complete by 8–9 years of age.
- Risk of recurrence if treatment is discontinued too soon.