To evaluate microvascular impairments with optical coherence tomography angiography (OCTA) in the eyes of diabetic patients with no diabetic retinopathy (NDR).
Systematic review and meta-analysis.
The PubMed and Embase databases were comprehensively searched to identify studies comparing the microvascular changes between diabetic eyes without clinical retinopathy and healthy controls using OCTA. Data of interest were extracted and analyzed by Review Manager V.5.3 and Stata V.14.0. The weighted mean differences and their 95% confidence intervals were used to assess the strength of the association.
Forty-four cross-sectional studies involving 2221 diabetic and 1838 healthy eyes were ultimately included. OCTA unambiguously revealed that compared with the healthy control group, the NDR group manifested enlarged areas and increased perimeters of the foveal avascular zone, with decreased perfusion density (PD) in the both superficial and deep capillary plexus of the macula (except parafoveal PD of the inner retina and foveal PD) and reduced radial peripapillary capillary PD. In addition, subgroup analyses according to the type of diabetes mellitus indicated that most of those differences became nonsignificant (except parafoveal PD in the deep capillary plexus) in type 1 diabetes mellitus, while in type 2 diabetes mellitus, they remained statistically significant.
Our results suggested that retinal microvascular impairments might have occurred antecedent to clinically visible diabetic retinopathy and could be detected early by OCTA. However, those manifestations could be inconsistent according to the types of diabetes mellitus.

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