Like other marine mammals, pinnipeds evolved from ancestors that lived on land. Modern pinnipeds feed underwater, but regularly haul onto land to warm in the sun, sleep, and reproduce. Their eyes have to work underwater, while still having some use on land. For underwater vision, pinniped eyes are large with extra curvature of their lens to bend light (which is how images are formed). Also helping them see in dim, ocean light are lots of light-sensitive cells and a membrane that reflects light back to the retina that otherwise would escape. On land, the extra lens curvature makes pinnipeds nearsighted (myopic). In bright, sunny conditions, such as reflective ice, their pupils close to a vertical slit to partly counteract the myopia. Whiskers on their noses that are highly sensitive to touch help them explore on land. In water, the whiskers may serve as motion detectors, picking up vibrations from fish or other objects.