Eyeworld

EW GLAUCOMA 30 by Michelle Dalton EyeWorld Contributing Editor Higher BMI linked to lower OAG risk in women A second population- based study has found a protective effect of higher BMI against OAG in women, but not men A new analysis of the Rot- terdam Study has found a higher body mass index (BMI) was associated with a lower risk of primary open-angle glaucoma (POAG) in women 1 , confirming results from the Nurses Health Study and Health Professionals Follow-up Study pub- lished last year 2,3 that obesity does, in fact, play a role in the risk of de- veloping POAG, but only in women. Other lifestyle issues, such as smok- ing and alcohol consumption, were not associated with an increased or decreased risk. "The inverse association of BMI with glaucoma was a bit surprising," said Wishal D. Ramdas, M.D., oph- thalmology and epidemiology de- partments, Erasmus Medical Center, Rotterdam, the Netherlands, and one of the study authors. "The fact that we have only found an associa- tion in women raises other ques- tions. One of them might be the involvement of female hormones in the pathophysiology of glaucoma." Dr. Ramdas and colleagues ana- lyzed data from the longitudinal, population-based Rotterdam Study to determine whether lifestyle-re- lated risk factors are associated with OAG. In this study (n=3939), the au- thors specifically analyzed the ef- fects on the incidence of OAG and on intraocular pressure. "We did not find any evidence for an association between income, education level, smoking, or alcohol intake and incident OAG," they said. Like the earlier studies, how- ever, a higher body mass seemed to have a protective effect on OAG in women but was also associated with higher IOPs. "The relationship between BMI and OAG and BMI and IOP seem to be contradictory," the authors said. "We could not find a significant as- sociation for BMI with cup-disc ratio, but independent of BMI, a higher waist-to-hip ratio was signifi- cantly associated with a smaller cup- disc ratio." In his opinion, Dr. Ramdas said, "probably the most important find- ing of the paper is the association of BMI with IOP. However, it is more likely that this finding was a result of the method of measuring IOP: Goldman applanation tonometry, performed behind the slit lamp. If a person is obese it is imaginable that the ophthalmologist has to push the slit lamp table against the breast of the patient, especially in women. It is conceivable this might work like a Valsalva maneuver (increased in- trathoracical pressure and, as a con- sequence, an increase in IOP)." Study details The Rotterdam Study was a prospec- tive, cohort-based evaluation of resi- dents at least 55 years old who live in the Netherlands. This study as- sessed income and education levels separately, and all other potential risk factors (smoking, alcohol con- sumption) were assessed from sub- ject questionnaires. Lifestyle risk factors that reach a P<0.20 in uni- variate comparisons were then in- cluded in multivariate analyses. People who developed OAG were considerably older, male, and had higher levels of myopia. At the univariate level, those with incident OAG had a lower BMI than the oth- ers, and the multivariate analysis in- dicated BMI was associated with a reduced risk of developing OAG. "Obese people are more prone to holding their breath during exam- ination, also causing a rise in IOP," Dr. Ramdas said. Study implications Although female hormones may play a role in the pathophysiology of glaucoma, "conflicting results have been reported on this, and fur- ther research is still needed," Dr. Ramdas said. Other studies 4 have found a pro- tective effect in men as well as women, "which may be explained by the characteristics of the study population," Dr. Ramdas said. For instance, participants in the Barba- dos Eye Study were predominantly of African descent, compared with the Rotterdam Study, where partici- pants were predominantly of Euro- pean descent; ethnicity is a confirmed risk factor for glaucoma. "More importantly," he said, "the number of glaucoma cases in their study was much higher than in our study. Therefore, they might have had more statistical power to detect significant differences be- tween BMI and glaucoma." For general ophthalmologists as well as glaucoma specialists, Dr. Ramdas suggested paying "extra at- tention when measuring a high IOP [using Goldman tonometry] in obese people, especially women." EW References 1. Ramdas WD, Wolfs RCW, Hofman A, de Jong PTVM, Vingerling JR, Jansonius NM. Lifestyle and risk of developing open-angle glaucoma. Arch Ophthalmol. Published online ahead of print Feb. 14, 2011. Doi:10.1001/archophthal- mol.2010.373. 2. Pasquale LR, Willett WC, Rosner BA, Kang JH. Anthropometric measure and their relation to incident primary open-angle glaucoma. Ophthalmology. 2010;117:1521-1529. 3. Dalton M. Women's BMI and risk of POAG. EyeWorld. 2010; November. http://eyeworld. org/article-women-s-bmi—-risk-of-poag. 4. Leske MC, Connell AM, Wu SY, Hyman LG, Schachat AP. Risk factors for open-angle glau- coma: the Barbados Eye Study. Arch Ophthal- mol. 1995;113(7):918-924. Editors' note: Dr. Ramdas has no finan- cial interests related to his comments. The study was funded by Topcon Europe BV (Capelle aan de IJssel, the Netherlands) and Heidelberg Engineering (Carlsbad, Calif.). Contact information Ramdas: w.ramdas@erasmusmc.nl February 2011 May 2011 30-33 Glaucoma_EW May 2011-DL_Layout 1 5/2/11 2:08 PM Page 30

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