Abstract
Background
Extensive evidence indicates that vasculopathy, especially the level of microcirculation, contributes to neurodegeneration in AD. However, it is not easy to direct monitor cerebral microcirculation. The retinal microvasculature has been used as a surrogate to study cerebral vascular changes. Indeed, decreased retinal microvascular network densities were reported in patients with AD. The goal of this project is to determine the retinal capillary function (RCF, the efficiency of blood flow transferring in the capillary network) in patients with Alzheimer’s disease (AD).
Method
Twenty patients (age 60‐84, mean ± SD: 72.8 ± 7.7 yrs) with AD and 14 age‐matched cognitive normal controls (CN, age 62‐81, mean ± SD: 68.6 ± 6.7 yrs) were recruited. There were no differences in vascular risk factors including smoking, hypertension, hyperlipidemia, type 2 diabetes, and cardiovascular disease between groups (Chi‐square test, all P > 0.05). One eye of each subject in both groups was imaged. Retinal blood flow (RBF) was measured using a Retinal Function Imager and retinal capillary density (RCD, expressed as fractal dimension Dbox) was measured using optical coherence tomography angiography. RCF was defined as the ratio of RBF to RCD.
Result
RCF was 1.62 ± 0.56 nl/s/Dbox (mean ± SD) in the AD group, which was significant lower than that (2.56 ± 0.25 nl/s/Dbox, P = 0.0001) in the CN group. The change of RCF in the AD group represented 28% lower than the CN group. RCF was significantly related to RBF in the AD group (r = 0.98, P < 0.05) and the CN group (r = 0.65, P < 0.05).
Conclusion
Our study is the first to demonstrate the impaired retinal capillary function in patients with AD. The alteration of RCF was mainly due to decreased retinal blood flow, which the capillary network can transfer. The RCF may be developed as a biomarker to study cerebral microcirculation in patients with AD.