Astigmatism refers to which condition?

• A. Inward turning of the eyelid rim
• B. Defective curvature of the cornea or lens of the eye
• C. Clouding of the lens
• D. Inflammation of the conjunctiva

Answer: (B)

Astigmatism happens when the cornea or the lens of the eye has an uneven curvature, so light doesn’t focus to a single point on the retina. Instead, refraction differs in different meridians, like an eggshell shape, which makes images appear blurred or stretched at all distances. The typical way to correct this is with lenses that add cylindrical power to balance the uneven curvature—eyeglasses with a cylindrical correction or toric contact lenses. In some cases, refractive surgery can reshape the cornea to produce a single focal point.

For context, the other conditions listed are distinct problems: inward turning of the eyelid is a misalignment issue of the lid, not a focusing error; clouding of the lens is cataract, which blocks light and creates hazy vision; inflammation of the conjunctiva is conjunctivitis, which affects the surface of the eye and its appearance and causes irritation.