Retinal Manifestations of Alzheimer's Disease: Insights from Animal Models, Clinical Detection, and Future Translation.
The retina, as an extension of the central nervous system, shares a common embryological origin with the brain. In Alzheimer's disease (AD), studies of human tissue and animal models have revealed that hallmark AD pathologies, including amyloid-β (Aβ) deposits and pathological tau protein tangles, also appear in the retina. These findings, coupled with advances in high-resolution retinal imaging techniques, suggest the potential to detect and characterize AD-related molecular and structural changes in the retina. However, retinal findings across different AD mouse models have significant discrepancies and show limited concordance with human phenotypes, complicating the identification of AD-specific alterations and the selection of optimal models for translational research. Moreover, the temporal sequence and functional significance of retinal abnormalities across the AD continuum, from preclinical stages to mild cognitive impairment and overt dementia, remain poorly defined. Addressing these knowledge gaps is essential to establish the retina as a reliable, non-invasive screening and monitoring approach. This review synthesizes current evidence on the spectrum of retinal alterations in AD, including vascular dysfunction, neuroinflammation, impaired Aβ clearance, and neurodegeneration, as observed in diverse mouse models. We compare these manifestations across species and between different models, highlighting findings along the disease continuum to delineate convergent and divergent pathways. We further discuss how emerging technologies enable the identification of AD-specific retinal alterations, and advocate for a paradigm shift from non-specific morphological assessment ("seeing shapes") toward molecular-level interrogation ("seeing components"). Interdisciplinary efforts and technological integration are crucial to establish retina as a dynamic mirror of pathology in AD.