Among lifestyle and socioeconomic factors only obesity appears to increase the risk of developing elevated intraocular pressure, and it might also protect women against developing open-angle glaucoma, according to new results from the Rotterdam Study published June 13 in Archives of Ophthalmology.
Given that individuals can modify several lifestyle and socioeconomic factors, Dr. Wishal D. Ramdas of Erasmus Medical Centre, Rotterdam, the Netherlands, and colleagues wanted to further investigate their association with glaucoma. To do so, they used data from the Rotterdam Study, a prospective, population- based cohort study of chronic diseases, including ocular disease, in residents aged 55 years and older living in a suburb of Rotterdam (Arch. Ophthalmol. 2011;129:767-72).
Patients underwent comprehensive eye examinations at baseline (1991 to 1993) and follow-up (1997-1999 and 2002-2006). Trained research assistants used questionnaires to determine patients’ income, education level, smoking habits, and alcohol intake. Researchers determined patients’ body mass index (BMI) and waist-to-hip ratio.
In this study, the researchers used data from participants who did not have open-angle glaucoma (OAG) at baseline and who completed at least one follow-up examination. They considered patients to have incident open-angle glaucoma (OAG) if neither eye had glaucomatous visual field loss at baseline and at least one eye did at follow-up.
During a mean follow-up of nearly 10 years, 108 of 3,939 participants (2.7%) developed OAG. Participants who developed OAG were significantly older, often had high myopia, and were more often male, the researchers found.
On regression analysis, the researchers found that BMI was associated with elevated intraocular pressure (IOP), yet seemed to reduce the risk of developing OAG. Further analysis, however, showed that this occurred only in women, who had a 7% decreased risk of developing OAG for each unit increase in BMI. There was no significant effect in men.
One possible explanation for the contrary findings, according to Dr. Ramdas and colleagues, is that excess fat tissue increases orbital and episcleral venous pressure. Also, obesity also may increase blood viscosity, resulting in outflow resistance of the episcleral veins.
Also, "with Goldmann applanation tonometry, the thorax and abdomen are pushed against the slit lamp table while breath holding works like a Valsalva maneuver," the researchers wrote. "This is especially relevant for obese women."
The apparent protective effect of obesity against OAG might really be a protective effect of high estrogen levels and hormone therapy. Obesity may be positively related to postmenopausal plasma estrogen levels.
There was no significant association between income, education, smoking, or alcohol intake with elevated IOP or OAG. Still, the researchers suggested caution in interpreting these results.
"Although these findings are in line with those from earlier studies, our findings are based on a relatively low number of OAG cases, and as a consequence, small effects of these lifestyle-related risk factors cannot be ruled out because of power limitations."
The Rotterdam Study is supported by the municipality of Capelle aan de IJsell and two Netherlands-based ophthalmologic devices companies. Additional funding was provided by Netherlands-based vision advocacy organizations.