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Vision loss is associated with increasing scores on the simplified severity scale for age-related macular degeneration (AMD) in the Age-Related Eye Disease Study. A correlation also has been found between vision loss and the four fundus lesions associated with advanced AMD. These findings suggest that the fundus lesions could be used as surrogates in prevention studies for development of advanced AMD.
Bethesda, MD-Vision loss is closely correlated with increasing severity on the simplified Age-Related Eye Disease Study (AREDS) Age-related Macular Degeneration (AMD) Severity Scale as well as with development of any of the fundus lesions of advanced AMD, including neovascular features and geographic atrophy.
Dr. Chew and colleagues reviewed data from more than 4,700 participants aged 55 to 80 years who were enrolled in AREDS, the goals of which include assessing the clinical course, prognosis, and risk factors for both AMD and cataract. The AMD trial included only the 3,640 subjects in the overall pool of participants who had at least early AMD at the time of enrollment. Median follow-up was 10.6 years in the AMD study cohort.
Visual acuity, on average, remained excellent over the study period in patients with no or few drusen at baseline who had not developed the fundus lesions associated with advanced AMD. For those who had large drusen at baseline but no development of AMD, the news also was good, said Dr. Chew.
The eyes in which any of the lesions associated with advanced AMD developed, however, had rapid declines in visual acuity, with a mean acuity of 20/200 or worse within 5 years of development of the lesion. In a composite of all four lesions, the decline from sub-retinal fibrosis was the most rapid.
Declines in visual acuity occurred more slowly in subjects with geographic atrophy rather than fundus lesions. On average, vision had reached 20/160 in about 5 years.
Enrollment for AREDS began in 1992, years before the availability of anti-vascular endothelial growth factor (VEGF) therapies, which lessen the degree of vision loss or improve visual acuity in some AMD patients. Few patients in the study underwent anti-VEGF therapy, although some had photodynamic therapy in the later years. As a consequence, data on the natural history of untreated AMD in a large patient pool, such as that accumulated during AREDS, are unlikely to be available to researchers in the future, Dr. Chew said.
She also discussed a patient-based scale (the simplified AREDS AMD Severity Scale) that uses both eyes and looks at the presence of large drusen, pigmentary abnormalities, and non-central geographic atrophy. Large drusen are defined as those with a diameter of 0.125 μm, approximately the width of a large vein at disc margin.
In that scoring system, physicians assign one point to each risk factor, such as drusen or pigmentary changes, in each eye. Risk factors are totaled for both eyes on a five-step scale (0 to 4). A score of 0, or no risk factor, represents a 0.5% risk; 1 factor, 3%; 2 factors, 12%; 3 factors, 25%; and 4 factors, 50% risk. A patient with large drusen and a pigmentary change would be given a score of 2 for that eye; if the same conditions were observed in the fellow eye, the total score would be 4. An eye with advanced AMD would be given a score of 2.
A score of 4 could be due to advanced AMD in one eye and pigmentary changes and drusen in the other; alternatively, it could be due to bilateral large drusen and bilateral pigmentary changes. In AREDS, 72% of patients with a score of 4 progressed to advanced AMD within 10 years, Dr. Chew said.