Researchers recently discovered many common systemic conditions have no association with keratoconus in the Korean population, with one important exception: allergic conjunctivitis. The researchers looked at data for 1,108,369 individuals and identified 613 with keratoconus, providing an adjusted incidence rate of 4.47 cases per 100,000 person-years. After matching each patient to five controls, the researchers found those who suffered from allergic conjunctivitis had a 37% increased chance of also being diagnosed with keratoconus compared with patients who did not have allergic conjunctivitis.

The researchers speculate the association is due, in part, to the eye rubbing that often accompanies allergic conjunctivitis. “Eye rubbing, a well-known risk factor for keratoconus, has been reported to not only induce mechanical damage to the cornea but also promote the production of tear inflammatory molecules,” the researchers wrote in their paper. They note the findings support the notion that ocular allergy is a significant risk factor for keratoconus.

Nonetheless, they found no association between keratoconus and atopy, eczema, asthma, connective tissue disorders, diabetes mellitus, sleep apnea or inflammatory bowel disease.

While atopy and eczema are seen as a form of allergy, they likely do not cause significant eye rubbing, the researchers wrote.