Researchers in New Zealand recently deemed keratoconus a multifactorial disease that is likely caused by a genetic predisposition and exacerbated through a “second hit” by environmental factors. The team reviewed the current literature from 15 countries and found that ethnicity and consanguinity are important determinants for geographical variations in keratoconus prevalence. At the top of the list of keratoconus risk factors were eye rubbing, atopy, floppy eyelid syndrome, contact lens wear, pregnancy and thyroid hormone disturbances.

The team noted that eye rubbing, atopy, floppy eyelid syndrome and contact lens wear can induce ocular surface inflammation, matrix metalloproteinase release and keratocyte apoptosis—findings that are consistent with the postulated etiology of keratoconus. Eye rubbing showed the strongest association with keratoconus.

The study reported that contact lens wear creates ocular surface inflammation akin to eye rubbing. It also reduces corneal nerve density, causes matrix remodeling and induces dry eye. However, because contact lens wear is a treatment for keratoconus, the investigators remarked that studying its role in progression is difficult.

The study authors are confident that their results will shed light on the development and progression of keratoconus. “Despite the progress made, further studies with large sample sizes will be required to truly understand the etiology of keratoconus,” they concluded in their paper. “Ideally, these studies will be sufficiently powered to allow multivariate analyses to tease out the role of each affected gene and each environmental factor on keratoconus development and progression.”

Crawford AZ, Zhang J, Gokul A, et al. The enigma of environmental factors in keratoconus. Asia Pac J Ophthalmol (Phila). December 4, 2020. [Epub ahead of print].