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G.-S. Ying, M. G. Maguire, J. Alexander, R. W. Martin, A. N. Antoszyk, the CAPT Research Group; The AREDS 9-Step AMD Severity Scale Applied to Participants in the Complications of Age-Related Macular Degeneration Prevention Trial (CAPT): Baseline Classification, Risk of Advanced AMD, and Longitudinal Path Analysis. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1762.
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To describe characteristics of the AREDS 9-step AMD severity scale applied to CAPT participants regarding baseline distribution, 5-year progression to advanced AMD, and changes on the scale over time.
Eligibility criteria for CAPT included having ≥ 10 large drusen (>125µ) and visual acuity ≥ 20/40 in each eye. One eye was assigned randomly to laser treatment and the fellow eye observed. Stereoscopic color fundus photographs were taken at baseline and annually thereafter for at least 5 years. CAPT Reading Center readers graded all the baseline photographs of observed and treated eyes (N=1,052 patients), and follow-up photographs of all the eyes that developed advanced AMD (N=220 eyes) and a random sample of observed eyes that did not develop advanced AMD (N= 280 eyes) according to the AREDS grading protocol. All eyes were graded for development of advanced AMD (choroidal neovascularization on fluorescein angiography or geographic atrophy involving the center of the fovea on color photographs).
Among 1,970 eyes with gradeable photographs meeting the drusen eligibility criterion, and free of advanced AMD at baseline, the 9-step severity scale for most eyes was 5 (11%), 6 (28%) or 7 (52%). Only 4% were at step 8 or 9. Among 984 observed eyes, the crude 5-year incidence rates of advanced AMD increased with each step between 4 and 7: 7% for step 4, 8% for step 5, 18% for step 6, and 22% for step 7. These rates were similar to those observed in the AREDS. Among the 316 observed eyes with all five annual photograph gradings available, 15.8% of eyes remained in the same scale step through 5 years, 35% of eyes increased 1 or more steps without reversals, 15% of eyes decreased 1 or more steps without reversals, 24% of eyes fluctuated within 1 or 2 steps, and 11% fluctuated more than 2 steps.
The AREDS 9-step AMD severity scale was predictive of the development of advanced AMD in eyes of CAPT participants. A high proportion of observed eyes (50%) deviated from an orderly progression through increasingly severe steps. This may limit use of the scale as an indication of progression of AMD.
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