Final answer:
A toric lens is used to treat myopia, hyperopia, and astigmatism. Myopia is corrected with a concave diverging lens, while hyperopia is fixed with a convex converging lens. Astigmatism requires a lens with different curvatures to correct uneven focus.
Step-by-step explanation:
A lens used to treat myopia/hyperopia and astigmatism is typically called a toric lens. Myopia, or nearsightedness, is a condition where distant objects appear blurry because the eye's shape causes light rays to focus in front of the retina. Hyperopia, or farsightedness, is where close objects are blurry because light rays focus behind the retina. In the case of myopia, a concave lens (also known as a diverging lens) is used to reduce optical power, helping to focus light properly onto the retina. For hyperopia, a convex lens (converging lens) is used to increase the optical power of the eye for proper focus. Astigmatism, which can accompany myopia or hyperopia, is corrected with a lens that has different curvatures to correct the uneven focus. While corrective lenses are commonly used, procedures like LASIK are alternative treatments to permanently change the shape of the cornea for improved vision.