A 30-year-old man has progressive astigmatism. Corneal topography shows a claw-shaped pattern of steepening confined to the inferior peripheral cornea with central normal curvature, marked thinning at the thinnest point just below the visual axis, and against-the-rule astigmatism. The MOST likely diagnosis is:
- A Classic keratoconus
- B Pellucid marginal degeneration ✓
- C Terrien marginal degeneration
- D Posterior polymorphous dystrophy
Correct answer: B. Pellucid marginal degeneration
Explanation
The butterfly or crab-claw pattern with inferior peripheral steepening, intact central cornea, and inferior crescentic thinning is characteristic of pellucid marginal degeneration. Classic keratoconus shows paracentral or central cone steepening with an asymmetric bowtie pattern. Terrien degeneration is distinguished by superior thinning with lipid deposition and a vascularised leading edge, and it produces against-the-rule astigmatism in older patients.
Reference: Cornea (Krachmer, Mannis, Holland), 4th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.