The number of keratoconus cases in the United States may be three times higher than previously reported, including a dense cluster in Western states, a recent study published in Eye & Contact Lens suggests.

A research team from the University of Maryland School of Medicine in Baltimore analyzed data from a 2016 VSP claims database and estimated the prevalence of keratoconus among enrollees by state.

Specifically, the prevalence of keratoconus among VSP enrollees in the United States during that year was estimated to be 0.15%, highest in Colorado (0.51%), and particularly acute in males between the ages of 18 and 34 and 40 and 64. The prevalence of keratoconus for each age group varied geographically and was notably higher in Western and Southern states.

Previous estimates of keratoconus prevalence in the United States were 0.054%, or one in 2,000 individuals, based on a landmark 1986 study from the Mayo Clinic. However, this study was limited to 64 newly diagnosed cases of keratoconus in a white population in Olmstead

County, Minnesota, and may not be applicable to other regions and populations in the country, the authors noted. A more recent study of Medicare beneficiaries in 2009 estimated keratoconus prevalence to be 0.018%.

The current study also noted a twofold increase over these prior estimates in Minnesota (0.09%).

The study also considered whether those living in sunnier states might be more at risk. Research on the link between exposure to sun or UV light and keratoconus has been mixed, the authors noted. For example, more exposure to sun or UV light, because of its oxidative effects on the cornea, may lead to a higher prevalence of keratoconus, they said. On the other hand, UV light has beneficial effects of inducing corneal stromal collagen crosslinking, the investigators added.

“This cross-sectional study provides some evidence supporting increased risk of keratoconus from sun or UV light exposure, yet some states with expected high exposure such as Florida and Hawaii defy this trend,” the researchers wrote in their paper. “As such, this association needs to be elucidated further in prospective studies.”

The highest national average for prevalence of keratoconus among VSP enrollees was reported in those aged 18 to 34 years followed by those aged 40 to 64 years, which was consistent with the onset, detection and progression of keratoconus commonly occurring in the later second to fourth decades of life, the investigators explained.

Future studies are needed to investigate variation in the prevalence of keratoconus by ethnicity or race and associated systemic health conditions, they added.