The degenerative corneal disease that results in irregular astigmatism is:

• A. Macular degeneration
• B. Presbyopia
• C. Keratoconus
• D. Diabetic retinopathy

Answer: (C)

Keratoconus is a degenerative thinning of the cornea that creates a cone-like protrusion. This abnormal shaping makes the corneal surface irregular, so the refractive power varies by meridian and produces irregular astigmatism. Because the curvature isn’t uniform, vision is distorted in ways that standard glasses often can’t fully correct; rigid contact lenses or scleral lenses can provide a more regular refracting surface to improve vision. Keratoconus is typically progressive, and management may include corneal cross-linking to slow progression or, in advanced cases, corneal transplantation. The other conditions affect other parts of the eye—retina or lens—not the cornea—and do not primarily cause irregular astigmatism.