Ms N.E is a 27-year-old female medical resident, with no previous medical history or any known keratoconus in her family of 2 brothers. She was prone to allergies in childhood. The patient complained of a progressive decrease in visual acuity greater to the left than in the right eye .
Her refraction at the first visit (03/08th/2016) was : Right Eye (RE) 20/20 with -3.25 (-1.25 x 80 °) and Left Eye (LE) 20/50 with -4 (-6.5 x 130 °). Analysis of previous refractions revealed that her astigmatism had increased over time.
Clinical examination with the slit lamp suggested a slight paracentral thinning more pronounced in the left eye .
We also found Vogt’s striae and Fleischer ring (Fleischer rings are pigmented rings in the peripheral cornea, resulting from iron deposition in basal epithelial cells, in the form of hemosiderin) in the left eye, associated with signs of dry eye (with a pathological tear film break up time).
Corneal topography revealed the presence of bilateral keratoconus more pronounced in the left eye.
When asked about the possibility of frequent eye rubbing, the patient admitted to the commencement of rubbing at the beginning of her medical studies. This timeline coincided with a progressive increase in the astigmatism in her spectacle prescriptions during that period.
As for her sleeping position, she claimed to sleep on her stomach at night, with her head positioned on the left side against the pillow. She is right-handed.
In the subsequent visits, she conveyed that she noticed rubbing her left eye more frequently while studying and after a shower, as it brought a sense of relief to her dry and tired eyes. She also had a habit of rubbing her eyes after removal of her contact lenses, which she had been wearing for 10 years. She subsequently became contact lens intolerant.
We explained to the patient that since vigorous rubbing had preceded the drop in visual acuity, this habit may have caused the cornea to deform in her case. We strongly advised this patient to stop rubbing her eyes and to change her unhealthy sleeping position.
Here are pictures of the patient rubbing her eyes and her profiles
In this case we find many triggers for eye rubbing like allergy, studying for prolonged hours and peculiar sleeping positions. The asymmetry in keratoconus development (left eye only) may be related to the sleeping position (left side) and the preferential rubbing of the left eye. Eye rubbing incites a local irritation and a vicious circle then ensues.
This case is very informative and demonstrative of the direct causal effect of eye rubbing in the pathogenesis of keratoconus.
Allergy is a classic risk factor for the disease, but it might be because allergic patients rub their itchy eyes more frequently and firmly than non-allergic patients. It has been shown that atopic (allergic) patients have a higher risk of keratoconus. Indeed, children and adolescents who rub their eyes vigorously because of itching and inflammation caused by the phenomena of ocular allergy (allergic conjunctivitis) may incite the development of keratoconus. The forces exerted on the corneal dome by the fingers and particularly the bones of the knuckles during are sufficiently intense to cause a rupture of the junctions connecting the collagen fibers of the anterior corneal stroma.
The corneal dome can be likened to a shell whose equilibrium geometry depends on the difference between the intraocular pressure (exerted on its posterior surface) and the atmospheric pressure. Beyond a certain threshold, the mechanical stresses (compression, shear) conveyed by eye rubbing results in a biomechanical embrittlement, due to the rupture of the harmonious arrangement of collagen fibers, which causes an irreversible deformation of the cornea (This mechanism is analogous to the « buckling » in resistance of materials).
This case is another compelling evidence that the cessation of eye rubbing and institution of proper allergy therapy are the best tools in the prevention of the genesis and/or evolution of keratoconus.