Localized interdigitation zone thinning in age-related macular degeneration

To assess prevalence and associations of localized thinnings of the interdigitation zone ("IZT") without adjacent drusen or reticular pseudodrusen in a general population, affected by age-related macular degeneration (AMD), or free of any other retinal disease. On optical coherence tomographic images, taken from the macula of participants of the population-based Beijing Eye Study, we searched for IZTs. The study population included 1271 eyes (mean age:64.7 ± 9.8 years; range:50-91 years). IZT prevalence increased from 2/442 (0.5%;95%CI:0.0,1.0) in the normal group to 49/543 (9.0%;95%CI:7.0,11.0), 90/275 (32.7%;95%CI:27.2,38.2), and 9/11 (81.8%;95%CI:55.0,100) in eyes with early, intermediate or late AMD (geographic atrophy), respectively. IZTs were spatially associated with ellipsoid zone (EZ) defects (114/150 (76.0%) eyes), external limiting membrane (ELM) defects (92/150 (61.3%) eyes), any intraretinal hyperreflective foci (iHRF) (143/150 (95.2%) eyes), iHRFs in the outer nuclear layer or beyond (111/150 (74.0%) eyes), macular hypopigmentation (76/150 (50.7%) eyes), and RPE hypertransmission (46/150 (30.7%) eyes), in addition to a non-spatial association with a higher prevalence of outer nuclear layer thinning (48/150 (32.0%) eyes). Higher IZT prevalence correlated (multivariable analysis) with higher AMD stage (OR:1.28;95%CI:1.08,1.51;P = 0.004), and higher prevalences of EZ defects (OR:7.97;95%CI:4.20,15.1;P < 0.001), iHRFs with a smoke-like appearance in the outer nuclear layer (OR:2.52;95%CI:1.32,4.82;P = 0.005), RPE hypertransmissions (OR:12.6;95%CI:2.92,54.7;P < 0.001), and outer nuclear layer thinning (OR:27.5;95%CI:6.12,123;P < 0.001). IZTs are a common feature of AMD including the early AMD stage. Their spatial association with defects in the overlying EZ, IHRFs and macular hypopigmentations may warrant further research of a potential involvement of an intraretinal RPE cell migration in the IZT etiology.