Abnormal rubbing and keratectasia

Hypotheses for the varied pathogenesis of the different forms of keratoconus have been outlined. Against this background, the possibility that abnormal rubbing causes or contributes to the development or progression of some forms of keratoconus has been examined.

Circumstantial evidence that shows an association between abnormal rubbing and keratoconus is reviewed, and a wide range of different forms of abnormal rubbing is described. Also examined is evidence of several processes whereby the cornea appears to be, or could be, adversely affected by mechanical trauma caused by rubbing. Conditions that may increase susceptibility to mechanical rubbing trauma have been discussed.

Evidence of a role for inflammatory mediators in the pathogenesis of keratoconus appears to void the description of keratoconus as a noninflammatory condition. When vigorous knuckle-rubbing forces are located on the normal peripheral cornea, the thinner or weakened cone apex may be exposed to high intraocular pressure distending forces that may tend to promote ectasia.

It appears reasonable to conclude that abnormal rubbing is a cause of some types of keratoconus, not because all abnormal rubbing, or only abnormal rubbing, leads to the development of some types of keratoconus, but because abnormal rubbing may increase the likelihood of the development of some forms of keratoconus. Abnormal rubbing habits may commence or continue after routine contact lens wear is established. Any associated rubbing or contact lens trauma may contribute to the progression of keratoconus. The abnormal rubbing-ectasia association in keratoconus may extend to other forms of keratectasia, including that seen after laser in situ keratomileusis, for which a contributory abnormal rubbing hypothesis may be appropriate.