Keratoconus is generally regarded as a corneal dystrophy of unknown origin. A dystrophy is defined as “any of various unrelated, non-infectious, often genetic disorders characterized by progressive deterioration or structural alteration of a body part”.
As opposed to this classic conception which has been adopted by most in the ophthalmic community, we believe that keratoconus is NOT a dystrophy for the following reasons:
– It has a low genetic or hereditary predisposition. About 80% of cases are sporadic, and no specific genetic mutation has been found despite intensive research. Any genetic association linked to keratoconus is often via a condition that incites eye rubbing eg atopic disease causing intense ocular pruritus.
– It has wide phenotypic expression. A dystrophy explains poorly how the disease could affect one eye more than the other, or sometimes be restricted to one eye (unilateral cases) only.
– It has an extremely variable age of onset. Keratoconus has been described to present between the 1st to 5th decades of life.
– Diseases associated with collagen abnormality, such as Marfan syndrome, do not share similar topographic features of keratoconus. Softer and thinner corneas in such cases do not exhibit large amounts of irregular astigmatism.
-Recent work has shown that the corneal damage in keratoconus is focal, suggestive of a local causative injury mechanism.
We believe instead that keratoconus corresponds to a clinical picture of a permanent corneal deformation caused by eye rubbing. Chronic repeated trauma inflicted on the eyeball results in a reduction of the biomechanical integrity of the corneal structures for reasons explained in detail here: “Eye rubbing: a sine qua non for keratoconus?“ and “No rub, no cone, the keratoconus conjecture”