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Posted: 11/4/2015

Delayed Rod-Mediated Dark Adaptation Is a Functional Biomarker for Incident Early Age-Related Macular Degeneration
Cynthia Owsley, PhD, Gerald McGwin, Jr., PhD, Mark E. Clark, BS, Gregory R. Jackson, PhD, Michael A. Callahan, MD, Lanning B. Kline, MD, C. Douglas Witherspoon, MD, Christine A. Curcio, PhD

To examine whether slowed rod-mediated dark adaptation (DA) in adults with normal macular health at baseline is associated with the incidence of age-related macular degeneration (AMD) 3 years later.

Prospective cohort.

Adults aged ≥60 years were recruited from primary care ophthalmology clinics. Both eyes were required to be step 1 (normal) on the Age-Related Eye Disease Study 9-step AMD classification system based on color fundus photographs graded by experienced and masked evaluators.

Rod-mediated DA was assessed at baseline in 1 eye after a photobleach using a computerized dark adaptometer with targets centered at 5 on the inferior vertical meridian. Speed of DA was characterized by the rod-intercept value, with abnormal DA defined as rod-intercept ≥12.3 minutes. Demographic characteristics, best-corrected visual acuity, and smoking status were also assessed. Log-binomial regression was used to calculate unadjusted and adjusted risk ratios (RRs) and associated 95% confidence intervals (CIs) for the association between baseline DA and incident AMD.

Main Outcome Measures
Presence of AMD at the 3-year follow-up visit for the eye tested for DA at baseline.

Both baseline and follow-up visits were completed by 325 persons (mean age, 67.8 years). At baseline, 263 participants had normal DA with mean rod-intercept of 9.1 (standard deviation [SD], 1.5), and 62 participants had abnormal DA with mean rod-intercept of 15.1 (SD, 4.0). After adjustment for age and smoking, those with abnormal DA in the tested eye at baseline were approximately 2 times more likely to have AMD in that eye (RR, 1.92; 95% CI, 1.033.62) by the time of the follow-up visit, compared with those who had normal DA at baseline.

Delayed rod-mediated DA in older adults with normal macular health is associated with incident early AMD 3 years later, and thus is a functional biomarker for early disease. The biological relevance of this test is high, because it assesses translocation of vitamin A derivatives across the retinal pigment epithelium and Bruch's membrane, 2 tissues with prominent age- and AMD-related pathology.

Organization: American Academy of Opthalmology

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