OP1.2 | Refractive Errors: Classification and Correction — Summary & Reflection

KEY TAKEAWAYS

Key takeaways — Refractive Errors: Classification and Correction:

• Myopia (short-sightedness): focal point anterior to retina; corrected with concave (minus) lens. Axial (commonest) vs refractive. Pathological myopia (>−6D) carries retinal complications: lattice degeneration, detachment, Fuchs' spot, staphyloma.

• Hypermetropia (long-sightedness): focal point would be posterior to retina; corrected with convex (plus) lens. Latent (compensated by accommodation) + manifest = total hypermetropia; cycloplegic refraction reveals the full error. Risk of accommodative esotropia in children.

• Astigmatism: different refracting power in different meridians; regular (WTR/ATR) vs irregular (keratoconus, scarring). Corrected with cylindrical lens (spectacle or contact lens); RGP for irregular astigmatism.

• Presbyopia: age-related (~age 40+), primarily due to loss of lens elasticity; corrected with plus add lenses (reading glasses, bifocals, progressives). Not a disease.

• Correction methods: retinoscopy (objective, essential for children) + subjective refraction = standard; cycloplegic refraction essential in children. Contact lenses (soft/RGP) — hygiene for Acanthamoeba risk. Myopia control (low-dose atropine 0.01%, orthokeratology).

• Red flag: no pinhole improvement → organic cause (cataract, macular disease, optic nerve, keratoconus). Unexpected 'improvement' in an older myope → suspect nuclear cataract (index myopia).

REFLECT

Reflect using Kolb's experiential learning cycle:

Concrete experience: A 10-year-old boy presents with poor school performance. The teacher suspects he cannot see the board. Examination shows distance VA 6/60 OD and 6/6 OS; he reads N6 in both eyes. There is no RAPD.

Reflective observation: What refractive error does the right eye history suggest? Why is the inter-eye asymmetry (anisometropia) clinically important in a child this age — and urgent?

Abstract conceptualisation: Using the concept of amblyopia (covered in OP1.5), explain why correcting a 10-year-old's refractive error is more time-sensitive than correcting the same error in a 30-year-old.

Active experimentation: If you were the treating ophthalmologist, what would be your prescription plan, and what would you tell the family about the consequences of non-compliance? How would your management differ if this child also had an esotropia?