Which of the following can affect visual acuity by extending across the cornea?

• A. Keratitis
• B. Pterygium
• C. Macular degeneration
• D. Cataract

Answer: (B)

Visual acuity can be reduced when a growth crosses onto the corneal surface from the conjunctiva. A pterygium is a fibrovascular growth that starts on the inner (nasal) conjunctiva and extends onto the cornea, sometimes reaching toward the pupil. As it encroaches on the cornea, it can change the corneal shape unevenly and cause irregular astigmatism or block part of the optical zone, leading to blurred vision or glare. That crossing of the corneal surface is why this condition affects acuity in this context.

Keratitis is inflammation of the cornea itself and can blur vision due to edema or scarring, but it does not involve a growth extending across the cornea from the conjunctiva. Macular degeneration affects the retina in the back of the eye, not the cornea. Cataract changes the lens inside the eye, away from the corneal surface.