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, researchers said.
Despite improvements in understanding the cause of this common yet life-altering condition, more work needs to be done, they said.
"The discovery that common genetic variants in the lysyl oxidase-like 1 gene (LOXL1) are associated with 99 per cent of XFS cases represented a significant advance in our understanding of this condition," said the study's lead author, Louis Pasquale, Associate Professor of Ophthalmology at Harvard Medical School (HMS).
"However, 80 per cent of control individuals also harbour 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," said Pasquale, who is also director of the HMS Glaucoma Centre of Excellence and Massachusetts Eye and Ear Glaucoma Service and Telemedicine Service.
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 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 US and Israel, involving XFS cases and control individuals (all 60 years or older, white individuals) enrolled from 2010 to 2012.
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 per cent increased odds of XFS.
Furthermore, every hour per week spent outdoors during the summer, averaged over a lifetime, was associated with a 4 per cent increased odds of XFS.
For every 1 per cent average lifetime summer time between the hours of 10 am and 4 pm that sunglasses were worn, the odds of XFS decreased by 2 per cent in the US, but not in Israel, researchers said.
The study was published in the journal Ophthalmology.