HISTOLOGY OF GEOGRAPHIC ATROPHY SECONDARY TO AGE-RELATED MACULAR DEGENERATION: A Multilayer Approach

Abstract

Purpose: To systematically characterize histologic features of multiple chorioretinal layers in eyes with geographic atrophy, or complete retinal pigment epithelium (RPE) and outer retinal atrophy, secondary to age-related macular degeneration, including Henle fiber layer and outer nuclear layer; and to compare these changes to those in the underlying RPE-Bruch membrane-choriocapillaris complex and associated extracellular deposits.

Methods: Geographic atrophy was delimited by the external limiting membrane (ELM) descent towards Bruch membrane. In 13 eyes, histologic phenotypes and/or thicknesses of Henle fiber layer, outer nuclear layer, underlying supporting tissues, and extracellular deposits at four defined locations on the non-atrophic and atrophic sides of the ELM descent were assessed and compared across other tissue layers, with generalized estimating equations and logit models.

Results: On the non-atrophic side of the ELM descent, distinct Henle fiber layer and outer nuclear layer became dyslaminated, cone photoreceptor inner segment myoids shortened, photoreceptor nuclei and mitochondria translocated inward, and RPE was dysmorphic. On the atrophic side of the ELM descent, all measures of photoreceptor health declined to zero. Henle fiber layer/outer nuclear layer thickness halved, and only Müller cells remained, in the absence of photoreceptors. Sub-RPE deposits remained, Bruch membrane thinned, and choriocapillaris density decreased.

Conclusion: The ELM descent sharply delimits an area of marked gliosis and near-total photoreceptor depletion clinically defined as Geographic atrophy (or outer retinal atrophy), indicating severe and potentially irreversible tissue damage. Degeneration of supporting tissues across this boundary is gradual, consistent with steady age-related change and suggesting that RPE and Müller cells subsequently respond to a threshold of stress. Novel clinical trial endpoints should be sought at age-related macular degeneration stages before intense gliosis and thick deposits impede therapeutic intervention.

Fig. 1.

External limiting membrane descent in an eye with geographic atrophy. ELM, external limiting membrane (green arrowheads); ILM, inner limiting membrane; NFL, nerve fiber layer; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; ISmy, inner segment myoid; ISel, inner segment ellipsoid; black arrowheads, Bruch membrane. The ELM descent is a curved line,^, and ONL subsides in parallel with it. The distances of −100 and −500 µm to the ELM descent (white triangles) represent assessment locations. Eighty-seven-year-old white man.

Fig. 2.

Geometry of Henle fiber layer in a normal macula. INL, inner nuclear layer; external limiting membrane, green arrowheads; IS, inner segment; ISmy, inner segment myoid; ISel, inner segment ellipsoid; OS, outer segment. Bar in (D) applies to all panels. Eighty-year-old woman. A. An en face view of henle fibers shows their radial dispersion from the foveal center. B–D. Indicate the locations of sections in (B), (C) and (D). B. In the superior perifovea are cross-sections of rods (yellow dots), cones (pink dots) with Müller cells in between (orange dots). C. In the perifoveal area of the central section, henle fibers are longitudinally oriented but short. A Müller cell (orange), rod (yellow) and cone (pink) photoreceptor are shown. One fiber is 115-µm long (from ELM to outer surface of OPL). Müller cell bodies, orange arrowheads. D. Close to the fovea in the central section, henle fibers are longitudinally oriented and long. One fiber is 350-µm-long (from ELM to outer surface of OPL). Müller, orange; rod, yellow; cone, pink.

Fig. 3.

Different presentations of the Henle fiber layer in eyes with geographic atrophy. INL, inner nuclear layer; external limiting membrane, yellow arrowheads; IS, inner segment; OS, outer segment. Bar in (D) applies to all panels. A. The ordered henle fibers in the central section are long and longitudinally oriented (1,400 µm to ELM descent, non-atrophic side), typical of normal retina but also a possible presentation in eyes with GA. Rod nucleus, pink arrowhead; cone nucleus, green arrowhead. Eighty-five-year-old woman. B. The henle fibers in the central section are disordered, having lost their longitudinal orientation (200 µm to ELM descent, non-atrophic side). Seventy-six-year-old woman. C. Ectopic photoreceptor nuclei (white arrowhead) in ordered HFL are seen at the central section (1,200 µm to ELM descent, non-atrophic side). Müller cell processes, orange arrowhead. Eighty-eight-year-old woman. D. The superior perifovea section of same eye as panel C, ectopic photoreceptor nuclei (white arrowheads) in disordered HFL are detected (900 µm to ELM descent, non-atrophic side). Photoreceptor nuclei ectopic to IS, black asterisks.

Fig. 4.

Thinning of outer nuclear layer in eyes with geographic atrophy. GCL, ganglion cell layer; IPL inner plexiform layer; INL, inner nuclear layer; external limiting membrane, yellow arrowheads; IS, inner segment; OS, outer segment; Bruch membrane, black arrowheads. Bar in (C) applies to (A) and (C); bar in (D) applies to (B) and (D). A and B. Outer nuclear layer in the central section is unremarkable, where more than four layers of photoreceptor nuclei are seen. Eighty-five-year-old woman. C and D. Outer nuclear layer in the central section is thin, with one to two layers of degenerative photoreceptor nuclei remained. Photoreceptor nucleus ectopic to HFL, white arrowhead in (D); Bruch membrane calcification, small black arrowheads in (D). Basal mounds, orange asterisks. Eighty-three-year-old woman.

Fig. 5.

Henle fiber layer and outer nuclear layer dyslamination in eyes with geographic atrophy. NFL, nerve fiber layer; GCL, ganglion cell layer; IPL inner plexiform layer; INL, inner nuclear layer; external limiting membrane (ELM), yellow arrowheads; IS, inner segment; OS, outer segment; Bruch membrane, black arrowheads. Bar in (E) applies to (A), (C) and (E); bar in (F) applies to (B), (D) and (F). A and B. Dyslamination of HFL and ONL in the superior perifovea (200 µm to ELM descent, non-atrophic side), which photoreceptor nuclei scattered into HFL and the boundary between HFL and ONL is not visible. Eighty-five-year-old woman. C and D. Dyslamination of HFL and ONL in the superior perifovea (at the border of ELM descent, non-atrophic side). Calcified drusen, pink arrowheads. Eighty-eight-year-old woman. E and F. Dyslamination of HFL and ONL at the central section (at the ELM descent, non-atrophic side). Subducted RPE cells, green arrowheads. Eighty-seven-year-old man.

Fig. 6.

Atrophy of outer nuclear layer in geographic atrophy. A. Meets the criterion for complete outer retinal atrophy (cORA) and (B), for complete RPE and outer retinal atrophy (cRORA). INL, inner nuclear layer; external limiting membrane (ELM), yellow arrowhead; RPE, retinal pigment epithelium; Bruch membrane, black arrowheads. Bar in (B) applies to (A) and (B). A. RPE is intact but HFL consists of Müller cells only and ONL is atrophic. ELM is visible (yellow arrowhead) as is the nucleus of a presumed degenerating photoreceptor (green arrowhead). Eighty-eight-year-old woman. B. Cone photoreceptor nuclei (green arrowheads) are present but do not form a continuous layer. ELM is not visible. BLamD is discontinuous (white asterisk). Bruch membrane calcification, black arrowheads. Eighty-five-year-old woman.

Fig. 7.

Pigment migration to outer nuclear layer and Henle fiber layer in eyes with geographic atrophy. ILM, inner limiting membrane; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; external limiting membrane, yellow arrowheads; IS, inner segment; OS, outer segment; Bruch membrane, black arrowheads. Bar in (C) applies to (A) and (C); bar in (D) applies to (B) and (D). A and B. RPE cells (white arrowheads in B) migrated to ONL and HFL. Bruch membrane calcification, black arrowheads in (B). Eighty-six-year-old woman. C and D. Melanosomes (white arrowheads and insets in D) migrated to ONL and HFL. Photoreceptor nucleus ectopic to IS, black asterisk in (D). Eighty-eight-year-old woman.

Fig. 8.

Five stages of choriocapillaris degeneration in eyes with geographic atrophy. ILM, inner limiting membrane; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; external limiting membrane, yellow arrowheads; IS, inner segment; OS, outer segment; RPE, retinal pigment epithelium; Bruch membrane, black arrowheads. Bar in (G) applies to (A), (C), (E) and (G); bar in (H) applies to (B) (D) (F) and (H). A1 and A2. The ChC, which fully occupies the arches of Bruch membrane, is unremarkable. Blood cells are detectable within the vessel. Eighty-eight-year-old woman. B1 and B2. The ChC are retracted (pink arrowheads), which fill up less than 50% of the area between two intercapillary pillars of Bruch membrane. Bruch membrane calcification, black arrowheads in (D). Eighty-three-year-old woman. C1 and C2. Ghost ChC (orange arrowheads), of which the endothelium are gone/fading, and a ghost ChC with a macrophage (green arrowhead) are detected. Basal laminar deposit is discontinuous (white asterisk). Eighty-three-year-old woman. D1 and D2. ChC in the de-pillared stage, where the intercapillary pillars of Bruch membrane have disappeared, as well as the endothelia and phagocytes. Basal laminar deposit is discontinuous (white asterisk). Eighty-three-year-old woman.