Retinal manifestations and their diagnostic significance in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition manifesting as cognitive decline, memory deterioration, and behavioral alterations. Late-onset AD accounts for most diagnosed cases, with the onset of symptoms usually occurring after 65 years. At present, there are no proven treatments that alter the course of AD. For early detection and intervention, it is crucial to understand the underlying mechanisms and identify promising biomarkers for AD. Research suggests that the pathological processes of AD initiate years before the emergence of noticeable symptoms, which makes the early diagnosis more challenging. While various biomarkers, such as cognitive tests, imaging, and biological markers in blood and cerebrospinal fluid, have been proposed for early detection, their reliability, as matched with symptomatic stages, varies significantly. As a component of the central nervous system, the retina has attracted attention as a potential site for studying AD-related changes. Studies from human and animal models have revealed structural, vascular, functional, and metabolic changes in the retina through the early phases of AD. Furthermore, advances in ophthalmic technologies have facilitated the identification and characterization of AD-related changes such as amyloid-β and tau-protein deposition. This review provides an overview and perspective on AD as they relate to the retina and highlights the importance of ocular changes as surrogates for understanding and diagnosing AD.