Peripheral Retinal Imaging Biomarkers for Alzheimer's Disease: A Pilot Study.

PURPOSE: To examine whether ultra-widefield (UWF) retinal imaging can identify biomarkers for Alzheimer's disease (AD) and its progression. METHODS: Images were taken using a UWF scanning laser ophthalmoscope (Optos P200C AF) to determine phenotypic variations in 59 patients with AD and 48 healthy controls at baseline (BL). All living participants were invited for a follow-up (FU) after 2 years and imaged again (if still able to participate). All participants had blood taken for genotyping at BL. Images were graded for the prevalence of age-related macular degeneration-like pathologies and retinal vascular parameters. Comparison between AD patients and controls was made using the Student t test and the χ2 test. RESULTS: Analysis at BL revealed a significantly higher prevalence of a hard drusen phenotype in the periphery of AD patients (14/55; 25.4%) compared to controls (2/48; 4.2%) [χ2 = 9.9, df = 4, p = 0.04]. A markedly increased drusen number was observed at the 2-year FU in patients with AD compared to controls. There was a significant increase in venular width gradient at BL (zone C: 8.425 × 10-3 ± 2.865 × 10-3 vs. 6.375 × 10-3 ± 1.532 × 10-3, p = 0.008; entire image: 8.235 × 10-3 ± 2.839 × 10-3 vs. 6.050 × 10-3 ± 1.414 × 10-3, p = 0.004) and a significant decrease in arterial fractal dimension in AD at BL (entire image: 1.250 ± 0.086 vs. 1.304 ± 0.089, p = 0.049) with a trend for both at FU. CONCLUSIONS: UWF retinal imaging revealed a significant association between AD and peripheral hard drusen formation and changes to the vasculature beyond the posterior pole, at BL and after clinical progression over 2 years, suggesting that monitoring pathological changes in the peripheral retina might become a valuable tool in AD monitoring.

Quantitative analysis of hydroxyapatite-binding plasma proteins in genotyped individuals with late-stage age-related macular degeneration.

Age-related macular degeneration (AMD) is associated with the formation of sub-retinal pigment epithelial (RPE) deposits that block circulatory exchange with the retina. The factors that contribute to deposit formation are not well understood. Recently, we identified the presence of spherular hydroxyapatite (HAP) structures within sub-RPE deposits to which several AMD-associated proteins were bound. This suggested that protein binding to HAP represents a potential mechanism for the retention of proteins in the sub-RPE space. Here we performed quantitative proteomics using Sequential Window Acquisition of all THeoretical fragment-ion spectra-Mass Spectrometry (SWATH-MS) on plasma samples from 23 patients with late-stage neovascular AMD following HAP-binding. Individuals were genotyped for the high risk CFH variant (T1277C) and binding to HAP was compared between wild type and risk variants. From a library of 242 HAP binding plasma proteins (1% false discovery rate), SWATH-MS revealed significant quantitative differences in the abundance of 32 HAP-binding proteins (p < 0.05) between the two homozygous groups. The concentrations of six proteins (FHR1, FHR3, APOC4, C4A, C4B and PZP) in the HAP eluted fractions and whole plasma were further analysed using ELISA and their presence in sections from human cadaver eyes was examined using immunofluorescence. All six proteins were found to be present in the RPE/choroid interface, and four of these (FHR1, FHR3, APOC4 and PZP) were associated with spherules in sub-RPE space. This study provides qualitative and quantitative information relating to the degree by which plasma proteins may contribute to sub-RPE deposit formation through binding to HAP spherules and how genetic differences might contribute to deposit formation.