Retinal phenotyping of variants of Alzheimer's disease using ultra-widefield retinal images

Retina pathology as a target for biomarkers for Alzheimer's disease: Current status, ophthalmopathological background, challenges, and future directions

There is emerging evidence that amyloid beta protein (Aβ) and tau-related lesions in the retina are associated with Alzheimer's disease (AD). Aβ and hyperphosphorylated (p)-tau deposits have been described in the retina and were associated with small amyloid spots visualized by in vivo imaging techniques as well as degeneration of the retina. These changes correlate with brain amyloid deposition as determined by histological quantification, positron emission tomography (PET) or clinical diagnosis of AD. However, the literature is not coherent on these histopathological and in vivo imaging findings. One important reason for this is the variability in the methods and the interpretation of findings across different studies. In this perspective, we indicate the critical methodological deviations among different groups and suggest a roadmap moving forward on how to harmonize (i) histopathologic examination of retinal tissue; (ii) in vivo imaging among different methods, devices, and interpretation algorithms; and (iii) inclusion/exclusion criteria for studies aiming at retinal biomarker validation.

Targeted Metabolomic Analysis of the Eye Tissue of Triple Transgenic Alzheimer's Disease Mice at an Early Pathological Stage

Alzheimer's disease (AD) is a severe neurodegenerative disease in older people. Despite some consensus on pathogenesis of AD established by previous researches, further elucidation is still required for better understanding. This study analyzed the eye tissues of 2- and 6-month-old triple transgenic AD (3 × Tg-AD) male mice and age-sex-matched wild-type (WT) mice using a targeted metabolomics approach. Compared with WT mice, 20 and 44 differential metabolites were identified in 2- and 6-month-old AD mice, respectively. They were associated with purine metabolism, pantothenate and CoA biosynthesis, pyruvate metabolism, lysine degradation, glycolysis/gluconeogenesis, and pyrimidine metabolism pathways. Among them, 8 metabolites presented differences in both the two groups, and 5 of them showed constant trend of change. The results indicated that the eye tissues of 3 × Tg-AD mice underwent changes in the early stages of the disease, with changes in metabolites observed at 2 months of age and more pronounced at 6 months of age, which is consistent with our previous studies on hippocampal targeted metabolomics in 3 × Tg-AD mice. Therefore, a joint analysis of data from this study and previous hippocampal study was performed, and the differential metabolites and their associated mechanisms were similar in eye and hippocampal tissues, but with tissue specificity.

Longitudinal change of reticular pseudodrusen area in ultrawide-field imaging

This study aimed to investigate the longitudinal change in the reticular pseudodrusen (RPD) area in the fundus and its association with late age-related macular degeneration (AMD). 91 RPD eyes (55 patients; age 67.9 ± 7.3 years) with > 5 years' follow-up (6.8 ± 0.9 years) from a single medical center were enrolled. Ultrawide-field photography images were analyzed using the concentric rings method, and the RPD area was semi-quantitatively classified according to the affected segment number into central, intermediate, and extensive types. Correlations of longitudinal changes in the RPD area and late AMD risk were investigated. RPD area increased significantly during the follow-up (p < 0.001). The increase rate correlated with age (r = 0.207; p = 0.048), RPD area at first visit (r = - 0.222; p = 0.035), and the decrease rate of subfoveal choroidal thickness (SFCT) (r = 0.217; p = 0.039). Many central (18/49, 36.7%) and intermediate (15/23, 65.2%) types switched to the more advanced type during the follow-up. Macular neovascularization and geographic atrophy developed in 12.3% and 18.7% of patients by 7 years. Late AMD incidence was significantly higher in eyes with large than in those with small RPD areas (p = 0.002). Larger RPD area at baseline, faster increase in RPD area, thinner SFCT, rapid decrease in SFCT, and the presence of late AMD on fellow eye were associated with late AMD. All RPD areas progressively increase over time. The regular assessment of RPD area may help to predict late AMD risk in RPD eyes.

Retinal phenotyping of variants of Alzheimer's disease using ultra-widefield retinal images

BACKGROUND

Posterior cortical atrophy (PCA) is the most common atypical variant of Alzheimer's disease (AD). Changes associated with PCA in the brain affect the visual cortex, but little is known about retinal changes in PCA. In this study, we explored retinal phenotypic variations in typical AD (tAD) and PCA.

METHODS

Retinal phenotyping was carried out on ultra-widefield (UWF) images of 69 control, 24 tAD, and 25 PCA participants.

RESULTS

Individuals with tAD (odds ratio [OR] = 2.76 [confidence interval (CI):1.24 to 6.10], P = .012) and PCA (OR = 3.40 [CI:1.25 to 9.22], P = .016) were more likely phenotyped as hard drusen. tAD (OR = 0.34 [CI:0.12 to 0.92], P = .035) were less likely to have soft drusen compared to control. Almost 3-fold increase in reticular pseudodrusen formation in tAD (OR = 2.93 [CI:1.10 to 7.76], P = .030) compared to control was estimated.

DISCUSSION

Studying the peripheral retina may contribute to a better understanding of differences in retinal phenotypes of different AD variants.