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Keratoconus (from Greek: kerato- horn, cornea; and konos cone) is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve.
Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light all often reported by the patient. It is typically diagnosed in the patient's adolescent years and attains its most severe state between the ages of 20 and 40. If afflicting both eyes, the deterioration in vision can affect the patient's ability to drive a car or read normal print.
In most cases, corrective lenses fitted by a specialist are effective enough to allow the patient to continue to drive legally and likewise function normally. Further progression of the disease may require surgery, for which several options are available, including intrastromal corneal ring segments, cross-linking, mini asymmetric radial keratotomy and, in 25% of cases, corneal transplantation.
Keratoconus affects around one person in a thousand; difficulties with differential diagnosis cause uncertainty as to its prevalence. It seems to occur in populations throughout the world, although it is observed more frequently in certain ethnic groups, such as South Asians. Environmental and genetic factors are considered possible causes, but the exact cause is uncertain. It has been associated with detrimental enzyme activity within the cornea, and is more common in patients with Down syndrome.

From wiki.

Keratoconus. Is not a blinding disorder ,but does result in increasing near -sightedness (things far away are out of focus) and irregular.