What type of lens is used to correct short-sightedness?

The correct response is the concave lens, which is used to correct short-sightedness, also known as myopia. Myopia occurs when the eye focuses images in front of the retina rather than directly on it, leading to blurry vision for distant objects. Concave lenses are designed to diverge light rays, thereby allowing the light to focus further back in the eye. They effectively extend the focal length, helping to bring the image onto the retina, which improves clarity for distant vision.

In contrast, convex lenses are used to correct farsightedness, where images are focused behind the retina. Convex-concave lenses and aspheric lenses serve specialized purposes in optics, often addressing more complex refractive errors but are not the primary corrective lenses for myopia.