The eye defect caused by an uneven curvature of the cornea or lens or both is

Step 1: Analyze the question The question asks which eye defect is caused by an uneven curvature of the cornea, the lens, or both.

Step 2: Explain the concepts Let's look at each option:

• Myopia (short-sightedness): The eyeball is too long, or the lens is too strong (too convex). Light focuses in front of the retina, so distant objects look blurred. It is corrected with a concave (diverging) lens.
• Presbyopia: An age-related defect. The lens loses elasticity, so the eye cannot focus on near objects. It is corrected with reading glasses (convex lenses or bifocals).
• Astigmatism: The cornea or lens is not perfectly spherical. One direction curves more than another, like the back of a spoon or a rugby ball. Light does not focus at a single point on the retina, so images look blurred or distorted. It is corrected with a cylindrical lens.
• Hypermetropia (long-sightedness): The eyeball is too short, or the lens is too weak. Light focuses behind the retina, so near objects look blurred. It is corrected with a convex lens.

Step 3: Match the definition "Uneven curvature of the cornea or lens or both" is exactly the description of astigmatism. The other three defects involve eyeball length or lens flexibility and strength, not an irregular curvature.

Step 4: Answer The correct option is C. astigmatism.

Exam tip: Think of the "A" in Astigmatism as meaning "Asymmetrical" curvature. Quick guide for the other defects:

• Myopia = Myopia, Myopic, "near is clear" (distant objects blurred)
• Hypermetropia = "far is clear" (near objects blurred)
• Presbyopia = Past-age (old age)