Keratoconus is an eye (ocular) disorder characterized by progressive thinning and changes in the shape of the cornea. The cornea is the thin, clear outer layer of the eye and is normally dome-shaped. Slowly progressive thinning of the cornea causes a cone-shaped bulge to develop towards the center of the cornea in the areas of greatest thinning. Affected individuals develop blurry or distorted vision, sensitivity to light (photophobia), and additional vision problems.
Source : rarediseases.org
Keratoconus is a long term and slowly-progressing condition, and is estimated to occur in between 1 and 6 people per 1000.
The cause is unknown, although eye-rubbing and allergies have been implicated. There also appears to be a genetic factor which increases the chances of developing the disease.
Note : The disease also leads to thinning of the Bowman's layerplugin-autotooltip__plain plugin-autotooltip_bigBowman's layer
"The Bowman's membrane (Bowman's layer, anterior limiting lamina, anterior elastic lamina) is a smooth, acellular, nonregenerating layer, located between the superficial epithelium and the stroma in the cornea of the eye. Source : Wikipedia"