Which refractive error is caused by irregular curvature of the cornea or lens?

• A. Myopia
• B. Hyperopia
• C. Emmetropia
• D. Astigmatism

Answer: (D)

Understanding how irregular curvature impacts focusing: when the cornea or lens isn’t evenly curved, light rays bend differently along different meridians and don’t meet at a single point on the retina. This creates two focal points in different directions, so vision becomes blurred or distorted at all distances. That pattern is astigmatism. It’s different from myopia, where distant objects focus in front of the retina due to excessive curvature or eye length; hyperopia, where near objects focus behind the retina due to insufficient refractive power; and emmetropia, which means the eye focuses light normally with no refractive error. Astigmatism is typically corrected with cylindrical lenses or certain surgical treatments that address the uneven curvature.