Late AMD represents potential public health problem

Fort Lauderdale, FL-Patients with age-related macular degeneration (AMD) who have a few small, hard drusen have little risk of progression to advanced stages of AMD over a 15-year period, the length of the Beaver Dam Eye Study. Individuals with large areas of drusen have increased risk of development of soft drusen or pigmentary abnormalities and progression to late AMD.

The 8% cumulative incidence of late AMD found in the Beaver Dam Study represents a potential public health problem because the population of older individuals is expected to increase by about 55% by the year 2025, according to Ronald Klein, MD, MPH, who reported the details of the analysis of the 15-year data at the annual meeting of the Association for Research in Vision and Ophthalmology.

The Beaver Dam Eye Study identified 5,924 individuals who were 43 to 84 years old between 1987 and 1988. During the following 2 years, 4,926 of these individuals were examined. Ultimately 3,684 were examined at the 5-year follow-up visit, 2,784 at the 10-year follow-up, and 2,119 at the 15-year follow-up, with the main reason for patients not participating in follow-up being death, Dr. Klein said. He is professor of ophthalmology and visual sciences, University of Wisconsin School of Medicine and Public Health, Madison.

Overall, 3,850 individuals had stereoscopic and nonstereoscopic photographs of AMD that were gradable at baseline and follow-up information that contributed to the estimates of the cumulative incidence of AMD. The disease was defined as early AMD, which included soft indistinct drusen or pigmentary abnormalities in the presence of drusen; and late AMD, which was defined by geographic atrophy or exudative AMD.

"We found 14% of the cohort over the 15-year period developed early AMD and did not have AMD at the baseline examination," he said. The pathologies observed varied from 8% with retinal pigment epithelial pigmentation to 32% for increased area of drusen.

The cumulative incidence of late AMD was 3.1%; 2% of the cohort developed exudative AMD and 1.3% developed geographic AMD. Some patients developed geographic AMD in one eye and exudative AMD in the fellow eye.

Dr. Klein demonstrated the increasing cumulative incidence of AMD with increasing patient age.

"For early AMD, the incidence varied from about 7% to 25% in the patients aged 65 to 74 years at baseline," Dr. Klein said. "For late AMD the incidence varied from about 3% to 8% in those patients who were 75 to 86 years at baseline. No significant differences were found between men and women or between left and right eyes in the incidence of early or late AMD."

Dr. Klein noted that the very small number of patients (13 patients) who were among the oldest patients precluded the investigators from evaluating the incidence of late AMD in these older patients. In 67 patients who were followed from the 10-year to the 15-year follow-up exams, the 5-year incidence of the development of geographic atrophy was 8%, which was nearly four times higher than that of exudative AMD, in these individuals who were 85 years old.

Size, type, and quantity

The drusen size, type, and quantity also seem to affect outcomes. Eyes with only one or two small, hard drusen-less than 63 µm in diameter at baseline-were less inclined to develop advanced disease. Eyes with about eight or more small, hard drusen averaging about 40 µm in diameter at baseline had an increased 15-year incidence of developing both soft indistinct drusen (18.3% versus 4.7%) and pigmentary abnormalities (10.9% versus 3.2%) compared with eyes with only one or two small, hard drusen. The eyes that had soft indistinct drusen or pigment abnormalities at baseline were much more likely to develop late AMD compared with eyes that did not have soft indistinct drusen (28.1% versus 1.3% and 19.6% versus 1.8%, respectively), according to Dr. Klein.