Quantification of capillary blood flow speeds in diabetic retinopathy using variable interscan time analysis (VISTA) OCTA

Purpose: To investigate retinal capillary plexus capillary flow speed and vessel density in diabetic retinopathy (DR) and normal subjects using variable interscan time analysis (VISTA) optical coherence tomography angiography (OCTA). Methods: High speed swept source OCTA imaging using multiple interscan times was performed over a 5 mm x 5 mm field-of-view with 600 kHz A-scan rate. Second-generation VISTA OCTA was used to measure a surrogate marker for capillary blood flow speed, VISTA flow speed (VFS), in the superficial and intermediate capillary plexuses, (SCP + ICP) VFS , and deep capillary plexus, DCP VFS . Vessel density was measured using OCTA. Results: Fifty-seven eyes with different DR severity and 37 normal eyes were analyzed. VISTA OCTA provided diverse blood flow speed information, including pseudo-color OCTA and mean flow speed in different regions. Both DCP VFS and DCP VFS /(SCP + ICP) VFS were higher in DR compared to normal eyes. Elevated DCP VFS correlated with decreased DCP vessel density in non-proliferative DR. Conclusion: VISTA OCTA can measure a quantitative biomarker for blood flow speed alterations in DR and normal eyes as well as the association with vessel density in different capillary plexuses. VISTA OCTA is promising for studies of pathogenesis and early flow alterations which may precede non-perfusion.