Keratoconus and eye rubbing

Keratoconus has long been labelled a “dystrophy of unknown origin”. Eye rubbing is acknowledged as a « risk factor » for keratoconus, but its importance has not been sufficiently emphasized, and may not reflect the prominent role eye rubbing plays in the genesis of keratoconus.
The deformation of the corneal wall in keratoconus is pronounced, yet surprisingly, few detectable genetic and molecular abnormalities exist in this condition. No “keratoconus gene” has been discovered.
The histological and biomechanical abnormalities observed in keratoconus are not diffuse but focal, located within the apical area of the cornea.
What could give such characteristic changes akin to shearing forces applied to the stress zones of the cornea?

EYE RUBBING

Eye rubbing has not been accorded sufficient prominence in the pathogenesis of keratoconus, and over time, through the management of thousands of patients with keratoconus, we have become increasingly convinced that eye rubbing is the root cause or sine qua non for keratoconus. As such, eye rubbing is not just a « risk factor », as often coined in the medical literature, but the direct cause of a syndrome with marked corneal deformation, and which we have labeled as « keratoconus ».

The « Marfan paradox » teaches us that softer corneas do not suffer from what is commonly observed in early and mild keratoconus: instead of becoming increasingly steep and irregular, they progressively distend and get globally flatter but not irregular.  In keratoconic eyes, « irregular deformation » or « warpage » may better describe the condition affecting the corneal wall than the term « ectasia », and  is caused by repeated local trauma due to the shearing forces inflicted by the hands, fingers and knuckles during eye rubbing episodes.

The mechanical trauma inflicted onto the corneal wall by chronic and incessant eye rubbing results in the progressive deformation and thinning which are hallmarks of the disease.

In many cases, the correlation between the sleeping position side and the side of worst warpage is striking.

Eye rubbing, exerted with fingers and knuckles in grinding or rotatory motions, submits the corneal wall to shearing forces.

Although eye rubbing is not necessarily sufficient to generate keratoconus in all patients who rub, repeated eye rubbing episodes constitute the necessary ingredient to develop keratoconic changes in the cornea. This is a key observation, as the suppression of eye rubbing offers the possibility of halting the progression of the disease, and even the opportunity to eradicate it.

Our intention is not blame keratoconus on patients. On the contrary, we, as part of the eye care community, are truly feeling responsible that eye rubbing has been such not been given importance in the genesis of the disease.

Figure legend : 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 the mechanical effects of 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 or mattress can cause local contamination and irritation. This, in turn, leads to local itch, which triggers eye rubbing, especially in the mornings. This explains also the asymmetry seen in many cases, and the striking correlation between the side which the patients sleep on and the side in which the clinical and topographic features of keratoconus are more severe.

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. 

In the Mechanical Hypothesis, keratoconus cannot occur without repeated mechanical injury such as with eye rubbing. When the duration and frequency of eye rubbing exceeds the native structural and biomechanical resistance capacity of the cornea, the mechanical imbalance causes the cornea to deform, leading to the characteristic topographical patterns, encompassing minor forms of deformation (keratoconus « forme fruste ») to frank or end stage keratoconus. In our experience, the latter is always encountered in patients who rub the affected eye vigorously and frequently.

A sprained ankle is caused by sudden excessive ligament extension. The pathogenetic mechanisms involved in the corneas of keratoconus share some similarities with that of a sprained ankle, but the damage inflicted by eye rubbing is not acute. Instead, it involves intensive and repetitive mechanical trauma to the corneal wall over a period of time .

Chronic eye rubbing can cause the corneal collagen fibers to lose part of their biomechanical resistance, resulting in macroscopically obvious structural deformation. This biomechanical mechanism could also better explain the frequent disparity in the degree of affliction between the right and left eyes (patients frequently rub one eye more often and more vigorously than the other) and the focal nature of keratoconus, which has been recently evidenced.

Figure legend :

The frequency of occurrence of keratoconus in close family members is not clearly defined, and estimated to be less than 20%. The exact genetics of keratoconus is still yet to be elucidated. In the hypothesis that eye rubbing is the root cause of keratoconus, the influence of genetics is related to the predisposition to conditions that lead to increased eye rubbing, and to variations in corneal thickness and resistance.  Down syndrome and atopy are obviously such conditions. Sleep apnoea has also been associated with an increased incidence of keratoconus. The deprivation of good quality sleep causes chronic fatigue and the need to rub the tired eyes. We have often observed cases of late onset keratoconus (after 30 years of age) in workers who had recently changed their work hours from day to night and experienced chronic fatigue from perturbation of their biological clock.

A recent male preponderance has been discovered in keratoconus. In our experience, women tend to rub their eyes less often and less aggressively than men when they wear eye make-up. However, some women with keratoconus tend to rub their eyes incessantly after removal of the eye make-up.

It is easier to connect the broad variations in the age of onset, laterality, asymmetry of severity and large spectrum of phenotypic expression with excessive eye rubbing than a corneal degeneration caused by an unknown genetic disorder or molecular cascade. For the same eye rubbing intensity, duration and frequency, corneas with native reduced thickness and biomechanical resistance may deform more significantly and quickly than thicker and stronger corneas.

Exposing populations with thinner corneas to high levels of pollution, dry air, irritating or allergenic agents and extreme working conditions may account for the prevalence of keratoconus in some socio-ethnic groups. The recent increased in computer usage has been linked to various ocular symptoms gathered in what is now called « Computer Vision Syndrome », and includes ocular fatigue, which elicits eye rubbing, which may play a role in the increase in the prevalence of keratoconus.

This website showcases the evidence that keratoconus is not a dystrophy of unknown genetics and biomolecular substratum, but rather a corneal deformation syndrome caused by EYE RUBBING.