Keratoconus occurs when the cornea — the clear dome-shaped window at the front of your eye — thins and bulges outward like a cone, bringing light rays out of focus and causing blurry, distorted vision.

The condition often starts in the late teens to early 20s and worsens over 10–20 years. In some cases it is genetic; about 1 in 10 people with keratoconus has a parent with the condition as well.