RPE morphometry in geographic atrophy due to AMD

Abstract

The geographic atrophy (GA) junctional zone includes changes in retinal pigment epithelium (RPE) and Bruch's membrane complex that are still difficult to interpret even with clinical high-resolution imaging technologies. We measured and evaluated degenerative RPE cell changes in histological sections of GA eyes. In this study seven GA eyes were evaluated by light microscopy. In three eye sections, zones of typical RPE alterations were graded (0= normal; 1= irregular cells but intact layer; 2= rounded, enlarged, and/or heaped cells; 3= migrating cells in retina; 4= RPE absent). In each graded zone, we measured and analyzed A)the total height of the RPE cell layer, B)the height of individual RPE cells and C)the height of basal deposits. From the outer macula towards the central RPE atrophic area the RPE passed almost steadily upward through grades of increased pathology. A)Zone2 exhibited highly variable total RPE height (16.9± 5.6 µm) with hypertrophic and heaped cells next to atrophic ones. In comparison, zone0 and zone1 showed less variability and aregular total RPE height (10.9± 2.6 µm). B)In zone2 the size of altered RPE cells varied widely (12.4± 5.2 µm, min.5.1, max. 27.5). All detected migrating RPE cells were hypertrophic. C)In zone0 basal deposits were found sporadically. With progressing RPE alterations, basal deposits became progressively continuous and thicker and reached aconsiderable height at the atrophic zone (9.5± 4.3 µm). Our measurements confirmed that degenerative RPE phenomena, particularly of degeneration grade2/3 close to the actual RPE atrophy zone, are often large enough to be visualized in detail with already available modern imaging technologies (e. g. SD-OCT).