|The cornea is essential to good vision. For example, the cornea filters out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the crystalline lens and the retina would be highly susceptible to injury from UV radiation.
If this "window" is curved too much, as is the case in some nearsighted people, faraway objects will appear blurry because distant light waves will refract imperfectly on the retina. If this "window" has imperfections or irregularities, as is the case in people with an astigmatism, light will refract unequally, causing a slight distortion of the visual image. But, if this "window" is of normal shape and curvature, light will refract with exquisite precision to the crystalline lens.