Eyeworld

77 EW GLAUCOMA February 2015 an etiologic role of early exposure to climatic factors on exfoliation glau- coma risk," Prof. Kang concluded. The nature of solar exposure matters The sun shines everywhere on earth, so why is there geographic variation in the prevalence of the disease? And if sun exposure is a risk factor, shouldn't the prevalence be higher in equatorial regions rather than lower, compared to more northern and southern climes? To better understand this seem- ing paradox, Aliya Jiwani, MD, in collaboration with the same group at Harvard that conducted the study described above, explored this issue in a 2-site case-control study that included patient cohorts from both Massachusetts and Israel. Cases had clinical evidence of anterior lens capsule exfoliation changes with or without glaucoma, and controls had normal anterior lens capsules and no glaucoma. Subjects were interviewed about residential and solar exposure histo- ry using validated questionnaires by interviewers masked to their case/ control status. As expected based upon the group's results above, every ex- tra hour per week spent outdoors increased the risk of exfoliation by 3%. Interestingly, every degree north or south of the equator that patients lived (using a weighted lifetime average latitude value) increased their relative risk by 11% compared to those who lived directly on the equator. Even more interestingly, a history of work over either snow or water increased the risk of exfoli- ation syndrome by nearly 4-fold among the U.S. participants, even after controlling for potential con- founding variables. As Dr. Jiwani pointed out, "The closer we are to the equator, the more directly the sun shines onto the surface of the earth, and the less chance there is for the sun to bounce off of surfaces into the eye. As we move away from the equa- tor, the sun is more angulated with respect to the horizon, creating a greater chance for reflection of light into the eye." Practical considerations We still do not fully understand the interplay between solar exposure and exfoliation syndrome. However, solar exposure has been implicated in other ocular conditions such as cataract and age-related macular degeneration, and minimizing exposure is warranted. Based on the theory of angulat- ed solar rays and distance from the equator, Dr. Jiwani said, "Sunglasses, but not a brimmed hat, may reduce the risk of exfoliation syndrome because sunglasses can better protect the eye from sunlight reflected off of the ground." EW Editors' note: Dr. Jiwani and Prof. Kang have no financial interests related to this article. Contact information Kang: nhjhk@channing.harvard.edu Jiwani: aliya_jiwani@meei.harvard.edu " In this U.S. study, greater time spent outdoors in young adulthood was associated with exfoliation glaucoma and suspect status, supporting an etiologic role of early exposure to climatic factors on exfoliation glaucoma risk. " –Jae Hee Kang, ScD

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