Overview
This lecture covers amblyopia (lazy eye), focusing on its definition, diagnostic criteria, types, causes, and clinical features relevant for diagnosis and management.
Definition and Diagnosis of Amblyopia
- Amblyopia ("lazy eye") is decreased visual acuity in one or both eyes due to abnormal binocular interaction or visual deprivation during early development.
- Typically, there is no detectable pathology in the retina or eye on physical exam.
- Clinical definition: in unilateral cases, a difference of two or more lines on the Snellen visual acuity chart between eyes; in bilateral cases, both eyes have visual acuity of 6/12 or worse.
- Amblyopia is reversible if detected and treated during the critical period (birth to 7–8 years).
- Severity: mild (6/9–6/12), moderate (6/12–6/24), severe (worse than 6/24).
Critical Period of Visual Development
- The critical period for visual pathway development is from birth to 7–8 years.
- Disruption in visual input during this period can cause amblyopia due to failure of proper visual pathway maturation.
Clinical Features and Suspicion
- Decreased visual acuity not improving with correction is a key sign.
- Children may show decreased contrast sensitivity, poor hand-eye coordination, and impaired depth perception.
- Other signs: closing or rubbing one eye, frequent squinting, head tilting, and blurred vision in one eye.
Classification of Amblyopia (by Cause)
- Strabismic Amblyopia: Due to squint (strabismus); the affected eye receives a blurred image, leading to suppression to avoid confusion.
- More common in esotropia (inward deviation) than exotropia (outward deviation) because of stronger suppression dynamics.
- Refractive Amblyopia: Caused by uncorrected refractive errors.
- Anisometropic: Significant difference in refractive power between eyes (hyperopia >1.5 D, myopia >3 D, astigmatism >2 D difference).
- Isometropic: Large, equal, uncorrected refractive errors in both eyes (myopia ≥5–6 D, hyperopia ≥4–5 D).
- Meridional: Due to uncorrected astigmatism >2–3 D in one axis in both eyes.
- Visual Deprivation (Sensory) Amblyopia: Caused by blockage of visual stimulus (e.g., congenital cataract, corneal opacity, ptosis, vitreous hemorrhage).
- Organic Amblyopia: Subtle undetectable retinal damage not visible on standard examination, detected only with advanced tests.
- Reverse Amblyopia: The previously healthy eye develops amblyopia due to prolonged patching of the normal eye.
- Idiopathic Amblyopia: No identifiable cause; may result from previously resolved risk factors in infancy.
Key Terms & Definitions
- Amblyopia — Reduced vision not correctable by glasses or pathologic findings, usually from abnormal visual experience in childhood.
- Strabismus — Misalignment of the eyes (squint).
- Anisometropia — Unequal refractive power between the two eyes.
- Isometropia — Equal but high refractive error in both eyes.
- Meridional Amblyopia — Reduced visual acuity due to uncorrected astigmatism in a specific axis.
- Critical Period — The developmental window (birth to 7–8 years) where visual experience shapes normal visual pathway maturation.
Action Items / Next Steps
- Review types and diagnostic criteria for amblyopia.
- Memorize refractive error cutoffs associated with amblyogenic risk.
- Prepare questions or clarifications for next session.