Value of the retina in the diagnosis of Alzheimer's disease

Abstract

AbstractVision, which is a process that requires the involvement of a large number of neurons, is often impaired during Alzheimer's disease (AD). Over the past few decades, research has shown that several visual functions and structures are compromised during AD and can also be used to differentiate affected individuals from those who show normal aging. Retina is a projection from the central nervous system and shares many features with the brain. Classically, the damage in AD was thought to be restricted mainly to the brain. However, in the last years it has been demonstrated in retinas of AD human postmortem specimens, the presence of Aβ plaques and pTau deposition, being more abundant in the superior region of the retina matching with greater neuronal degeneration. Also, it has been suggested that Aβ plaques in the retina may anticipate those in the brain. In addition, recently it has also been possible to observe in vivo Aβ plaques in human retinas, with imaging techniques and ingesting curcumin as a marker of Aβ deposits. Recently, using in vivo hyperspectral imaging techniques in the retina, it has been reported that Aβ load in the brain can be predicted. These findings provide histopathological evidence that the visual system may be altered much earlier in the AD disease process than previously thought, and thus support the use of visual biomarkers in the early detection of the disease. Current in vivo imaging techniques such as OCT are allowing ophthalmologists to detect and quantify data consistent with the histopathological findings described in the retinas of AD patients. In early AD, OCT has demonstrated a thickening of the macular region and a subsequent thinning of the peripapillary area of the retina in more advanced stages of the disease. New analytic methods have shown in AD patients that thinned regions are interspersed with thickened ones in all retinal layers, except inner nuclear and outer segments. This causes roughness to appear on retinal layer thickness maps, finding that Fractal Dimension (FD) of retinal layers is greater in the AD patients, being roughness of retinal layers, assessed by the FD of their thickness maps, a possible early retinal biomarker of AD.In the other hand, recent data suggest the vascular involvement of the retina in AD patients. Vascular changes in the retina are thought to share similar pathogenic mechanisms with cerebral vasculature. OCT and OCT angiography (OCTA) has demonstrated a thinning of the choroidal thickness in early AD and decrease of the foveal avascular zone in patients with moderate AD.All these observations support the value of the retina as a biomarker of AD that will allow us, with the development of new research, to discover new retinal biomarkers that will help us to improve the diagnosis and follow‐up of this growing pathology.