The effects of eye rubbing
Is eye rubbing the root cause of keratoconus?
Damien Gatinel MD, PhD
Chronic and vigorous eye rubbing is the main and necessary causative factor of keratoconus rather than just another risk factor among others in the evolution of the condition, according to Damien Gatinel MD, PhD.
“The time has come to challenge the common conception of keratoconus as a dystrophy of unknown genetics and biomolecular substratum. I believe that keratoconus is primarily a mechanical and behavioural disease in which the sleeping position plays a key role maybe by reducing the corneal resistance and also triggering some rubbing,” said Dr Gatinel, speaking at the World Ophthalmology Congress (WOC) in Barcelona.
Summing up his theory as “no rub, no cone”, Dr Gatinel said that his clinical experience looking at hundreds of case histories of keratoconus patients is that the absence of rubbing may actually prevent keratoconus from occurring in the first place.
“We believe the problem is that eye rubbing has been positioned as a risk factor, but when you think about it the other risk factors for keratoconus are more risk factors for eye rubbing than keratoconus itself. Eye rubbing is the only risk factor that is exerted directly against the cornea, and the force that is applied with the fingers or knuckles can sometimes be as high as the force resulting from the pressure in a car tyre,” he said.
Dr Gatinel said that not every eye rubber will develop keratoconus but that patients with the particular “keratotype” of an existing thin and weak cornea are particularly at risk.
“I often use the analogy of sunburn to explain what I feel about this association between keratoconus and eye rubbing. There are risk factors for sunburn, such as light skin and exposure to the sun at certain times of the day. But what causes the sunburn is the UV light. So we have risk factors and a phototype, but if there is no UV there is no sunburn. Likewise, I believe that if there is no rubbing there is no cone and that there are certain keratotypes which may expose you to keratoconus if you rub and you have a thin or a soft cornea,” he said.
The orthodox teaching is that keratoconus is an unknown genetic dystrophy that leads to cornea weakening through a series of factors involving the reduction of collagen/elastin, extracellular matrix degradation and collagenase and enzymatic activity, among others, said Dr Gatinel.
“However, the literature shows that only 14% of cases are non-sporadic, so it does not really fit the bill of a true genetic disease. It also does not explain why left and right eyes can be affected very differently and there has been no gene found yet despite many family studies conducted,” he said.
The theory that inflammation triggered by dry eye syndrome may be responsible for keratoconus initially seems plausible, said Dr Gatinel, since surface inflammation can lead to impaired surface barrier and temperature rise triggering a cascade leading to corneal weakening.
“The problem with this theory is that inflammation usually causes flattening, not steepening as in cases of diffuse lamellar keratitis or stromal keratitis. Furthermore, even if you believe in the theory of surface inflammation and dystrophy there is still a major issue in that a soft cornea is not a keratoconus cornea,” he said.
Dr Gatinel noted that Marfan syndrome should perfectly support the theories of keratoconus that attempt to explain the ectatic process. In Marfan syndrome, the gene mutation is identified, and the molecule involved in this connective tissue dystrophy is responsible for the reduction of the strength of the collagen present in the ocular tissues, including the corneal stroma.
“However, despite all these features no keratoconic ectatic pattern is seen in the corneas of patients with Marfan syndrome. The Marfan corneas are thinner but tend to be flatter instead of steeper,” he said. These characteristics (progressive thinning and stretching causing corneal flattening) may in fact better correspond to the term “ectasia” than what is observed in keratoconus. The focality of the corneal damage pleads in favour of a local vulnerate agent, which is the repeated trauma inflicted by the patient’s fingers. Over time, the applied force results in a progressive thinning and focal steepening of the corneal wall. Keratoconus, from form fruste to severe, corresponds to variable levels of permanent warpage caused by a corneal buckling of primarily mechanical origin.
Summing up, Dr Gatinel advised doctors to warn their patients of the deleterious effects of chronic and vigorous eye rubbing.
“If our ‘no rub, no cone’ conjecture is correct then we must have stabilisation when people stop rubbing, or else there are other factors involved. I am happy to say that all of our cases apart from three, which we have documented on our website defeatkeratoconus.com, are stable. The three patients who have not stabilised all continue to rub their eyes,” he said.
Damien Gatinel: firstname.lastname@example.org