Keratoconus is a type of corneal ectasia, which refers to a group of diseases in which the cornea is thinned and weakened. The name is derived from the Greek word for “horn” (keratos) and “cone” (konos) – “I have a horn-cone on my eye” (said no one, ever).  As the corneal tissue thins, the pressure inside the eyeball may push outward and distort the cornea into a cone shape, leading to distorted vision. Think of a balloon with a weakness in one particular spot – this area will bulge outwards more than the rest of the balloon. While keratoconus does not cause total blindness, vision impairment may progress to the point of causing legal blindness. In the US, legal blindness is defined as a visual acuity of less than 20/200, or a visual field of 20 degrees or less.

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