Eye rubbing , a sine Qua Non for Keratoconus ?

Keratoconus, a dystrophy of unknown origin, remains an ophthalmic enigma. The contrast between the presence of marked structural changes and deformation of the corneal wall and the relative absence of specific genetic and biomolecular findings continues to intrigue ophthalmologists. In Marfan syndrome, where genetic and molecular abnormalities are well identified, and similar changes in collagen observed, the cornea tends not to be steeper, irregular or ectatic, but are globally flatter. This suggests that an external mechanical force may be necessary to induce the apparition and progression of the ectatic process in keratoconus. Eye rubbing has long been acknowledged as a risk factor for keratoconus and its progression, but could it in fact be the root cause? Many clinical observations and reports support the hypothesis of eye rubbing as a first and necessary hit for inducing progressive ectatic deformation of the corneal wall. Validating or refuting this hypothesis on the basis of patient admission may be impossible. It is difficult to document the frequency, duration and intensity of eye rubbing in patients with keratoconus, and virtually impossible to prove that every patient who denies the habit truly does not rub his eyes. Both the increase in incidence of atopy and the time spent in front of the computer screen in the general population may account for an increased tendency for eye rubbing, and lead to the perceived increased prevalence of keratoconus in both urban and non-urban areas. This paper explores the possibility that the mechanical stress imposed on the cornea by rubbing may not be as much a second hit evoking the structural changes of a predisposed cornea exhibiting unknown collagen progressive alteration, but rather the necessary trigger and sine qua non of the keratoconic process. Even if this provocative hypothesis is impossible to prove, it is equally difficult to refute, and acknowledging eye rubbing as a possible root cause increases awareness within the general population and if true, could dramatically reduce the incidence of keratoconus, and halt its progression in eyes already affected.