Retinal vessel density and cognitive function in healthy older adults.

The eye is considered a gateway to the brain, as the retina is the only tissue of the central nervous system not protected by bones. This enables non-invasive imaging to provide exceptional insights into the brain. Based on the similarity of brain and retinal structure, it is being investigated whether changes in retinal blood flow could serve as a potential biomarker for cognitive decline. Optical coherence tomography angiography (OCTA) enables an examination of the microcirculation of the retina on the basis of retinal flow registration. Retinal blood flow has been associated with cognitive function and changes have been shown for Alzheimer's patients, whereas data for healthy older subjects are contradictory. The aim of this study was to correlate OCTA parameters with the individual performance in tests assessing the executive functions (EFs) inhibition, updating and shifting in a group of healthy older adults (range: 65-79) using structural equation modeling, with hematocrit serving as a mediator. A model was obtained for vessel density (VD) of the retinal superficial vascular complex and the EF parameters inhibition and updating. The model revealed that only the mediator hematocrit correlated with EF, whereas neither the direct path VD to EF nor the indirect path VD via hematocrit to EF were significantly correlated. Regression analysis with hematocrit yielded significant results for the variable updating. We conclude that higher levels of hematocrit shorten reaction time and the coefficient of variation increases correspondingly, indicating a positive effect of hematocrit on EF.