The connection with allergies and keratoconus.
Perhaps the most frequent question when a diagnosis of keratoconus is made is, “Why me?”
There are a number of theories: some scientists are sure the answer can be found in the genes, others are positive the answer can be found in the environment. A majority of doctors seem to favor a ‘two hit’ theory – someone with a genetic predisposition to KC experiences an environmental trigger that sets the disease progression in motion.
Eye rubbing is considered by many the most common and controllable environmental trigger.
But like the chicken and the egg, does vigorous eye rubbing cause KC, or is there a reason why people with KC rub their eyes more?
That might be answered by looking at the connection between allergies and KC. Some studies have concluded that KC patients have more allergies or more severe allergies than the general public. Other studies found no difference in the percentage of people (KC vs. non-KC) with allergies.
Last year, a study conducted in Tehran, Iran enrolled 2,411 participants (885 KC patients and 1,526 with no evidence of KC)(1). Study subjects completed questionnaires about their allergy history. The authors did not find a significant difference between the two groups. Their conclusion was that allergies were no more prevalent in the KC community than the general public.
Then they looked more closely at the KC group. Of the 885 KC patients, just over half (n=449) had a history of allergic diseases. The authors compared KC patients with allergies to KC patients without allergies (n=436) and found that patients with a history of allergies had more severe disease, and patients who reported ocular allergies had the highest incidence of severe KC. The authors concluded that ocular allergies seem to impact KC more than other allergies like asthma, rhinitis, eczema or food or drug allergies, which may not trigger eye rubbing.
“That is not surprising,” according to Dr. Marjan Farid, MD, a cornea specialist at Gavin Herbert Eye Institute. “We encourage patients who experience red, swollen, and teary eyes resulting from ocular allergies to start treatment as soon as possible to minimize eye rubbing, especially those patients with keratoconus. Your eye doctor can prescribe treatments like antihistamine eye drops that provide relief from itchy, irritated eyes.”
Despite studies like this large scale survey, the debate continues: do ocular allergies make KC worse, or do patients with severe KC experience more ocular allergies?
Naderan M, Rajabi MT, et al Effect of Allergic Diseases on Keratoconus Severity, Ocular Immunology and Inflammation 25:418-423, 2017.