Optical coherence tomography angiography in Parkinson’s disease: a systematic review and meta-analysis

Background To examine the association between optical coherence tomography angiography (OCTA) retinal measurements and Parkinson’s disease (PD). Methods We searched MEDLINE and EMBASE from inception up to November 5th, 2021 for studies examining the differences between OCTA retinal measurements in PD patients and healthy controls. We used the Hartung–Knapp–Sidik–Jonkman random-effects method to combine study-specific standardized mean differences (SMD) in pooled effect estimates and a meta-analytic extension of the E-value metric to quantify the confounding bias capable of nullifying the pooled estimates. Results Nine eligible studies for our systematic review were identified through our search strategy. The pooled SMD between the retinal vessel density of PD patients and healthy participants in the whole superficial vascular plexus (SVP), foveal SVP, parafoveal SVP and foveal avascular zone (FAZ) was −0.68 (95% CI: −1.18 to −0.17, p value = 0.02, n = 7 studies), −0.14 (95% CI: −0.88 to 0.59, p value = 0.62, n = 5 studies), −0.59 (95% CI: −1.41 to 0.23, p value = 0.12, n = 5 studies) and −0.20 (95% CI: −0.79 to 0.38, p value = 0.39, n = 5 studies), respectively. An unmeasured confounder would need to be associated with a 3.01-fold, 1.54-fold, 2.81-fold and 1.70-fold increase in the risk of PD and OCTA retinal measurements, in order for the pooled SMD estimate of vessel density in whole SVP, parafoveal SVP and FAZ, respectively, to be nullified. Conclusions Our results provide evidence on an inverse association between whole SVP vessel density and PD.