Keratoconus is a progressive steepening of the cornea that usually begins in adolescence through middle age. Our modern corneal topographers and tomographers (sensitive instruments that analyze the curvature and elevation of the front and with the most advanced instruments the back of the cornea, corneal thickness, and statistical measures of corneal structural health can now measure early and advanced measures of keratoconus. They can also detect eyes that are predisposed to developing keratoconus or corneal ectasia after having refractive surgery. Keratoconus can be equal in both eyes or asymmetrically worse in one eye compared to the other. It can be caused by firm eye rubbing, genetic diseases, or allergic diseases. It can interfere with clear vision by causing irregular astigmatism from thinning and elevation of the cornea. People with earlier keratoconus can see well with glasses; in more advanced cases gas permeable contact lenses can provide excellent vision. Many cases of keratoconus or corneal ectasia can be improved, arrested, or slowed down by Collagen Cross-Linking by applying Riboflavin to the cornea which acts as a photo mediator and is activated by applied ultraviolet light to cause the corneal collagen fibrils to polymerize and strengthen. Corneal Crosslinking is now available in the United States in Clinical Trials approved and monitored by the United States Food and Drug Administration (FDA). Sometimes it can be improved by implanting Intracorneal Ring Segments and in other cases requires Corneal Transplantation to improve vision.