Autofluorescence Characteristics of Early, Atrophic, and High-Risk Fellow Eyes in Age-Related Macular Degeneration

Abstract

To assess the relationships of drusen, pigment, and focally increased autofluorescence (FIAF) and the reticular pattern of hypoautofluorescence, to distinguish the combined photographic and AF characteristics of early, atrophic, and high-risk fellow eyes in AMD. In a retrospective interinstitutional clinical study, AF and color photograph pairs of 221 eyes were examined: 166 eyes of 83 patients with bilateral large, soft drusen, with and without geographic atrophy (GA), and 55 fellow eyes of 55 patients with unilateral choroidal neovascularization (CNV). Forty-two eyes (one eye from each of 42 patients with early or atrophic AMD) were divided into four groups: 14 with drusen only, 9 with drusen and pigment abnormalities, 11 fellow eyes of patients with unilateral GA, and 8 eyes of patients with bilateral GA (acronyms for the groups: D-D, D-Pig, D-GA and GA-GA, respectively). The 55 fellow eyes of patients with CNV were divided into three groups: 19 eyes with no FIAF (CNV-0), 16 with FIAF without reticular AF (CNV-1), and 20 eyes with reticular AF and/or pseudodrusen (CNV-R). Image pairs of eyes with FIAF were registered, and drusen, pigment, and FIAF were segmented using automated background leveling and thresholding. All 221 eyes were surveyed for reticular AF and reticular pseudodrusen. The main outcome measures were (1) the fraction and relative probability of FIAF colocalizing with drusen and pigment and (2) the presence or absence of reticular AF and reticular pseudodrusen. The mean fractions of FIAF that colocalized with large drusen were: D-D group, 0.46 +/- 0.21; D-Pig group, 0.42 +/- 0.29; D-GA group, 0.13 +/- 0.09; and GA-GA group, 0.11 +/- 0.12. Comparisons between groups showed significant differences when comparing either the D-D group or the D-Pig group with either the D-GA group or the GA-GA group (P between 0.0001 and 0.015), whereas other comparisons were nonsignificant (Mann-Whitney rank sum test). The mean probabilities of FIAF colocalizing with large drusen relative to chance (1.0) were: D-D group, 4.7 +/- 2.5; D-Pig group, 4.3 +/- 2.3; D-GA group, 1.4 +/- 0.8; and GA-GA group, 1.8 +/- 1.3, with similar significant differences as for the colocalization fractions. The mean probability of FIAF colocalizing with small to intermediate drusen in the D-D group was 1.5 +/- 1.3, which was not significantly different from chance. In the D-Pig group, the median probability of FIAF colocalizing with pigment abnormalities was 10.0 (range, 1.1-51.0). The AF patterns in 15 of 19 eyes in the CNV-0 group were normal; the remainder had nonreticular hypoautofluorescence only. In the CNV-1 group, the relations of FIAF with drusen and pigment were similar to those in the early AMD groups. CNV-R comprised 20 of 55 eyes in the CNV group, but reticular autofluorescence and/or pseudodrusen were found in only 14 of 166 eyes of the early and atrophic groups. Of the 34 total eyes with reticular AF or pseudodrusen, 28 had both, 4 had reticular AF only, and 2 had reticular pseudodrusen only. There are clear relationships between AF patterns and clinical AMD status. In early AMD, FIAF's colocalization with large, soft drusen and hyperpigmentation is several times greater than chance, suggesting linked disease processes. In advanced atrophic AMD, FIAF is found mostly adjacent to drusen and GA, suggesting that dispersal of drusen-associated lipofuscin is a marker of atrophic disease progression. In the neovascular case, a large group of fellow eyes have no FIAF abnormalities, suggesting that lipofuscin is not a major determinant of CNV. However, reticular hypoautofluorescence, consistent with widespread inflammatory damage to the RPE, appears to be a highly sensitive imaging marker for the disease that determines reticular pseudodrusen and is strongly associated with CNV.