Exfoliation syndrome (XFS) is an eye condition that is a leading cause of secondary open-angle glaucoma and can lead to an increased risk of cataract and cataract surgery complications. 

Despite improvements in understanding the cause of this common yet life-altering condition, there are a lot of unknowns, like what factors are most likely to cause it.

What are some of those factors? Residential geography, time spent in the sun, and whether or not sunglasses are worn, according to a study published in JAMA Ophthalmology.

"The discovery that common genetic variants in the lysyl oxidase-like 1 gene (LOXL1) are associated with 99 percent of XFS cases represented a significant advance in our understanding of this condition," says Louis Pasquale, M.D., Associate Professor of Ophthalmology at Harvard Medical School (HMS) and the paper's lead author. "However, 80 percent of control individuals also harbor these variants and that ratio of cases to control individuals with trait-related variants is fairly similar in regions where XFS is very prevalent and in regions where the condition is relatively rare; this suggests that other genetic or environmental factors contribute to XFS."

Although previous studies have shown that residential (geographic) history and extent of solar exposure may be important risk factors for XFS, detailed lifetime solar exposure had not previously been evaluated. Researchers from Mass. Eye and Ear, Brigham and Women's Hospital, Harvard Medical School, Goldschleger Eye Institute, Chaim Sheba Medical Center, Tel Aviv University, Tel Hasomer Israel, Case Western Reserve University, and New York Eye and Ear Infirmary set out to assess the relationship between residential history, solar exposure and XFS in the study.

They conducted a clinic-based, case-control study in the United States and Israel, involving XFS cases and control individuals (all 60 years or older, white individuals) enrolled from 2010 to 2012 (United States: 118 cases and 106 control participants; Israel: 67 cases and 72 control individuals) They measured weighted lifetime average latitude of residence and average number of hours per week spent outdoors as determined by validated questionnaires.

They found that each degree of weighted lifetime average residential latitude away from the equator was associated with an 11 percent increased odds of XFS. Furthermore, every hour per week spent outdoors during the summer, averaged over a lifetime, was associated with a 4 percent increased odds of XFS. For every 1 percent average lifetime summer time between the hours of 10 a.m. and 4 p.m. that sunglasses were worn, the odds of XFS decreased by 2 percent in the United States, but not in Israel.

In the United States, after controlling for important environmental covariants, the history of work over water or snow was associated with increased odds of XFS. In Israel, there were too few people with this history for analysis. Researchers did not identify an association between brimmed hat wear and XFS. Complete results are available in the study.

"Lifetime outdoor activities may contribute to XFS," said Dr. Pasquale. "The association between work over snow or water and the lack of association with brimmed hat wear suggests that ocular exposure to light from reflective surfaces may be an important type of exposure in XFS etiology. If confirmed in other studies, there could be reason to consider more widespread use of UV-blocking eyewear in these cases to help prevent XFS."