Subclinical inflammation predicts macular disease

By Joanna Lyford, Senior medwireNews Reporter

Levels of high-sensitivity C-reactive protein (hsCRP) predict the risk for age-related macular degeneration (AMD) and diabetic macular edema, show results of two independent studies published in JAMA Ophthalmology.

The findings are significant because they point to inflammation as an underlying pathologic mechanism and raise the possibility that inflammation could be useful both as a risk marker and a target for therapy.

The first study was a pooled analysis of five large cohorts: the Women's Health Study, the Physicians' Health Study, the Women's Antioxidant and Folic Acid Cardiovascular Study, the Nurses' Health Study, and the Health Professionals Follow-up Study.

All participants were free of AMD at baseline and 647 developed AMD during follow-up. Logistic regression analysis found that participants with hsCRP levels greater than 3 mg/L at baseline were up to 2.59 times as likely to develop AMD as those with levels below 1 mg/L.

After adjusting for confounders and heterogeneity among studies, the pooled odds ratio (OR) for incident AMD for high versus low hsCRP levels was 1.49. The risk for neovascular AMD was also increased among people with high hsCRP levels, with an adjusted OR of 1.84.

Debra Schaumberg (Brigham & Women's Hospital, Boston, Massachusetts, USA) and co-authors remark: "This information might shed light on underlying pathological mechanisms involving inflammation and could be of clinical utility in the identification of persons at high risk of AMD who may benefit from increased adherence to lifestyle recommendations, eye examination schedules, and therapeutic protocols."

In the second study, Rajeev Muni (University of Toronto, Ontario, Canada) and team performed a prespecified subanalysis of the Diabetes Control and Complications Trial, which included 1441 young adults with Type 1 diabetes.

All participants were assessed at baseline for markers of subclinical inflammation, including hsCRP and intercellular adhesion molecule-1 (ICAM-1).

After adjustment for treatment assignment and other factors, baseline hsCRP levels were significantly associated with the risk for clinically significant macular edema and for the development of retinal hard exudates, with relative risks (RR) of 1.83 and 1.78 for the top versus bottom quintiles.

Levels of ICAM-1 at baseline were also associated with the risk for retinal hard exudates, with a RR of 1.50.

The researchers say their study demonstrates that hsCRP may predict the risk for incident clinically significant macular edema, the leading cause of vision loss in working-aged individuals in North America.

"With further research, these findings may lead to a better understanding of the mechanisms underlying the development of clinically significant macular edema and retinal hard exudates and may lead to more effective strategies for retinopathy prevention and management," they write.

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