What part of the eye is affected in keratoconus?

The cornea is the clear, transparent front covering which admits light and begins the refractive process. It is this clear convex cornea which bends (refracts) a ray of light and slows it down. It also shrinks the light to a manageable size (a little smaller than a one rupee coin). It is this front covering of the eye that is affected in keratoconus.