Keratoconus
Keratoconus (also known as &amp;#8220;conical cornea&amp;#8221;) is a degenerative disease of the eyes that manifests itself as a gradual degradation of the cornea into a more conical form than the typical eyeball. 
This condition can cause extreme nighttime vision distortion, sensitivity to light, itching, &amp;#8220;ghost&amp;#8221; images and some distortion of daytime vision. The etiology of this condition is not fully understood, though it&amp;#8217;s known that proteases break down many of the keratin bonds in Bowman&amp;#8217;s layer of the cornea, causing a relaxation of the tissues. 
In most patients with keratocornea, the degradation will &amp;#8220;settle&amp;#8221; at a degree that can be corrected by glasses. In 25% of patients, however, corneal transplant may be called for, in order to allow nighttime vision and increased sight during the day.
Diseases of the Eye: Number One. Moorfields Manchester Institute of Ophthalmology, The Medical Illustration Department, pre-1950.