What is astigmatism? Astigmatism is usually due to the refractive surface not being perfectly spherical, which is usually the cornea or the lens. ...

Astigmatism is a common vision condition that causes blurred or distorted vision. It occurs when the cornea or lens of the eye has an irregular shape, causing light to focus on multiple points instead of a single point on the retina. This can result in difficulties with both near and distance vision. Regarding the given statements: I. Astigmatism is usually due to the refractive surface not being perfectly spherical, which is usually the cornea or the lens. II. The light from a point source produces a linear image on the retina. III. Astigmatism can be corrected with lenses that have different curvatures in two mutually perpendicular directions. The correct option would be: b) I and II are correct. Statement I explains the cause of astigmatism, which is the irregular shape of the cornea or lens. Statement II describes how light from a point source forms a linear image on the retina in the case of astigmatism. However, statement III is incorrect because astigmatism is corrected with lenses that have different curvatures in one direction, not two mutually perpendicular directions. I hope this clarifies your question! Let me know if you have any more doubts.