Eye rubbing as the root cause of keratoconus?
Keratoconus has been labelled a “dystrophy of unknown origin”, and I have long been fascinated by this mysterious disease. A large proportion of my clinical practice is dedicated to the diagnosis, management and prevention of keratoconus, and for many years I have been intrigued by how structural changes and deformation of the corneal wall are so pronounced in keratoconus, yet paradoxically, few detectable genetic and molecular abnormalities exist in this condition.
Eye rubbing has long been acknowledged as a risk factor for keratoconus, but I believe its role in the pathogenesis of keratoconus has not been accorded sufficient prominence. I have thus undertaken the task to pen an article to suggest to readers a pathophysiological concept of keratoconus that I am increasingly convinced of: that eye rubbing is the root cause or sine qua non for keratoconus (article download). As such, eye rubbing is not a « risk factor », as often coined in medical litterature, but the direct cause of a syndrome marked by a corneal deformation labeled « keratoconus ».
In this article, I have put forth the theory that keratoconus is not a dystrophy of unknown genetics and biomolecular substratum, but rather a syndrome caused by eye rubbing. i.e what has been called “keratoconus” is in essence the direct consequence of mechanical trauma to the cornea by chronic and incessant eye rubbing, resulting in the progressive deformation and thinning of the corneal wall which are hallmarks of the disease. Eye rubbing is the main character of the « mechanical » hypothesis as the etiology of keratoconus:
The Molecular Hypothesis vs the Mechanical Hypothesis illustrated in a schematic diagram. The Mechanical Hypothesis states that keratoconus is primarily caused by eye rubbing. Eye rubbing is mainly triggered by atopy, air pollution, and extended computer screen viewing. In contrast to the Molecular Hypothesis where genetics, environmental and other unknown general factors are keys to the apparition of the disease, the Mechanical Hypothesis simply states that the structural corneal changes and deformation are initiated and aggravated by a mechanical cause: eye rubbing. Additional mechanical factors, such as corneal refractive surgery or night compression of the cornea (by pressure of the hand or pillow) may also accelerate the corneal deformation. The prolonged contact between the eye and eyelids with the pillow of mattress can cause local contamination and irritation. This, in turn, leads to local itchness, and triggers eye rubbing, expecially in the morning. This explains the striking correspondence between the » head side » on which patients sleep and the topographic features evocative of keratoconus. Eye rubbing can cause inflammation. The effect of the mechanical stress (distension) is further accentuated by the release of proteinases in the stroma, explaining the progressive thinning of the cornea, which in turn makes it more vulnerable to the trauma caused by rubbing. LASIK cause eye-dryness, and this can in turn trigger eye rubbing, on a more vulnetable (thinned by the refractive surgery procedure). In the Mechanical Hypothesis, keratoconus cannot occur without a repeated mechanical injury such as eye rubbing. When the duration and frequency of eye rubbing exceed the native structural and biomechanical resistance capacity of the cornea, the mechanical imbalance causes the cornea to deform, leading to characteristic topographical patterns, encompassing minor forms of deformation (keratoconus « forme fruste ») to the end stage KC. In my experience, the latter is always encountered in patients who rub the affected eye vigorously and frequently.
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