BOSTON (Sept. 4, 2014) -- Residential geography, time spent in the sun, and whether or not sunglasses are worn may help explain why some people develop exfoliation syndrome (XFS), 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, according to a study published on Sept. 4 in JAMA, Ophthalmology.
Despite improvements in understanding the cause of this common yet life-altering condition, more work needs to be done. "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," said the study's lead author, Louis Pasquale, M.D., Associate Professor of Ophthalmology at Harvard Medical School (HMS), and director of the HMS Glaucoma Center of Excellence and Mass. Eye and Ear Glaucoma Service and Telemedicine Service. "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.
Researchers 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."
This work was supported by the Arthur Ashley Foundation, grant EY020928 from the National Institutes of Health (Dr. Janey Wiggs), a Physician-Scientist Award from Research to Prevent Blindness (Dr. Pasquale), a Harvard Medical School Ophthalmology Scholar Award (Dr. Pasquale) and a Dorris Duke Charitable Foundation grant (Dr. Aliya Jiwani). Dr. Wiggs received an honorarium for travel expenses from Research to Prevent Blindness.
A full list of authors and the affiliations is listed in the study.
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Mass. Eye and Ear clinicians and scientists are driven by a mission to find cures for blindness, deafness and diseases of the head and neck. Led by the Eaton-Peabody Laboratory in Otology, the Howe Laboratory in Ophthalmology and Schepens Eye Research Institute, Mass. Eye and Ear in Boston is the world's largest vision and hearing research center, offering hope and healing to patients everywhere through discovery and innovation. Mass. Eye and Ear is a Harvard Medical School teaching hospital and trains future medical leaders in ophthalmology and otolaryngology, through residency as well as clinical and research fellowships. Internationally acclaimed since its founding in 1824, Mass. Eye and Ear employs full-time, board-certified physicians who offer high-quality and affordable specialty care that ranges from the routine to the very complex. U.S. News & World Report's "Best Hospitals Survey" has consistently ranked the Mass. Eye and Ear Departments of Otolaryngology and Ophthalmology as among the top hospitals in the nation.