Imagine looking into a crystal ball, but instead of predicting the future, it reveals early signs of Alzheimer’s disease (AD) and mild cognitive impairment (MCI). That’s what researchers have discovered by studying the tiny blood vessels in the retina. In this comprehensive review, scientists analyzed data from multiple studies to evaluate changes in retinal microvasculature in patients with AD and MCI. They found that the density of blood vessels in both the superficial and deep layers of the retina was reduced, suggesting impaired blood flow early on in these diseases. Additionally, the foveal avascular zone, an area without blood vessels, was significantly enlarged in AD patients. By using a special imaging technique called optical coherence tomography angiography (OCTA), researchers were able to detect these retinal changes, offering a potential biomarker for early detection and intervention. The study also revealed that the type of OCTA machine used and the size of the scan area influenced the results, emphasizing the importance of standardized methods in future research. This exciting research opens up new possibilities for monitoring disease progression and developing targeted treatments. For more information, check out the original article!

BackgroundThe remarkable increase in prevalence and significant morbidity of neurodegenerative diseases pose a tremendous burden for the health care system. Changes in retinal microvasculature metrics associated with Alzheimer’s disease (AD) and mild cognitive impairment (MCI) may provide opportunities for early diagnosis and intervention. However, the role of retinal vascular biomarkers remains controversial. We aim to perform a systematic review, meta-analysis and meta-regression to evaluate the comprehensive retinal microvasculature changes in patients with AD and MCI.MethodsWe conducted a literature search on PubMed, MEDLINE, and EMBASE to identify studies published before May 2021 which assessed the measurements of optical coherence tomography angiography (OCTA) between AD, MCI with healthy control eyes, including foveal avascular zone (FAZ), vessel density (VD) of peripapillary, superficial and deep capillary plexus, and choroidal thickness using a random-effect model. We also performed meta-regression and subgroup analysis and assessed heterogeneity and publication bias to evaluate potential sources of bias.ResultsCompared with control eyes, VD of superficial capillary plexus was significantly lower in AD [standardized mean difference (SMD): −0.48; 95% CI (−0.70 to −0.27); p = 0.04] and MCI eyes [SMD: −0.42; 95% CI (−0.81 to −0.03); p = 0.03], as well as reduced VD of deep capillary plexus [SMD: −1.19; 95% CI (−2.00 to −0.38]; p < 0.001], [SMD: −0.53; 95% CI (−0.85 to −0.22); p < 0.001]. FAZ was significantly enlarged in AD eyes [SMD: 0.54; 95% CI (0.09 to 0.99); p = 0.02]. The meta-regression analysis showed that the OCTA machine type and macular scan size significantly influenced the variation of VD and FAZ between AD and control eyes (p < 0.05).ConclusionOur results highlight the potential of OCTA as a biomarker to detect early microvasculature deficits in AD and MCI. Notably, the macular scan size and different OCTA machine type could explain the heterogeneity observed in literatures. This information might be useful for future longitudinal study design to evaluate the role of OCTA in monitoring disease progression and treatment efficacy.

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