Corneal topography shows central corneal steepening with an inferior-superior asymmetry index (I-S value) > 1.4 D and a best-fit sphere of 50 D centrally. Pachymetry shows inferior corneal thinning. Which condition is most likely?
- A Pellucid marginal degeneration
- B Megalocornea
- C Lattice dystrophy
- D Keratoconus ✓
Correct answer: D. Keratoconus
Explanation
Central corneal steepening, inferior-superior asymmetry (I-S ratio > 1.4 D), inferior corneal thinning on pachymetry, and steep simulated keratometry are hallmarks of keratoconus on topography. Pellucid marginal degeneration also causes inferior thinning but the cone is peripheral (20-30° inferior) producing a 'crab-claw' or 'kissing birds' pattern. Lattice dystrophy is a stromal dystrophy without these topographic features.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.