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Gregory R. Jackson, Laura E. Walter, Ingrid U. Scott, Mark E. Clark, Mitchell G. Brigell; Twelve-Month Progression of Dark Adaptation Impairment in Patients with Early to Intermediate AMD. Invest. Ophthalmol. Vis. Sci. 2011;52(14):121.
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The purpose of the study is to determine whether dark-adaptation (DA) can be used as an endpoint for early age-related macular degeneration (AMD) proof-of-concept studies. A more sensitive endpoint to early disease than visual acuity will increase the feasibility of preventative AMD clinical trials. We report the results of a 12-month natural history study of DA in healthy adults and patients with early to intermediate AMD. The primary goal is to determine whether delay in DA increases over a 12 month interval.
DA was measured at 3 time points: baseline, 6-months, and 12-months. Rod-mediated DA was measured using the AdaptRx (Apeliotus Technologies, Atlanta GA). A clinically significant change was defined as a 3 min change of the rod intercept. Visual acuity was measured with the E-ETDRS. A significant change was defined as a 15 letters change. Three-field stereo photographs were taken for grading using the 11-step AREDS AMD severity scale. A significant change in fundus appearance was defined as a 3-step change.
At baseline, 47 patients were enrolled and 31 patients completed the study. Reasons for attrition include: drop outs (7), unreadable photographs (4), unusable dark adaptation data (4) and misdiagnosis (1). The sample consisted of 4 normal adults, 4 patients with borderline AMD, and 23 patients with early to intermediate AMD. At 12-months, progression of DA impairment occurred in 6/23 (26%) of the AMD patients and regression occurred in 1/23 (4%). Visual acuity worsened in 2/23 (9%) of AMD patients. No participant’s disease progressed as assessed by fundus grading.
Six (26%) AMD patients had a significant decrease in DA speed over a 12 month interval. The worsening of dark adaptation was not correlated to a change in AREDS severity scale or acuity. It has been postulated that increased DA timing in AMD patients reflects depletion of vitamin A in the RPE as a result of impaired transport across Bruch’s membrane. If this is the case, then it might be expected that patients with a progressive abnormality of DA are at higher risk for conversion to advanced AMD. This cohort of patients will be followed to determine if this is the case. This study suggests that dark adaptation may be suitable functional biomarker for early proof-of-concept studies evaluating novel treatments for early to intermediate AMD.
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