Why the correct answer is right
A cylinder lens has two different powers in its principal meridians, which is the exact design needed to correct for astigmatism. An astigmatic eye has two different focal points due to its irregular shape (usually of the cornea). A cylinder lens is designed to neutralize this difference, bringing the two focal points together into a single point on the retina.
Why the other options are incorrect
Myopia and hyperopia are corrected with simple spherical power, as the focus is the same in all meridians. Presbyopia is the age-related loss of near focus and is corrected with an "add" power in a multifocal lens.
Memory aid
Think of an astigmatic eye as being shaped like a football (a toric surface). You need a lens that is also shaped like a football (a **cylinder** lens) to correct it.
Real-world application
Any prescription that contains a second and third number (e.g., -1.00 **-0.50 x 180**) is a prescription for astigmatism. The second number is the cylinder power, and the third is the cylinder axis. These values tell the lab how to grind the toric surface onto the lens.
