Impact of Lens Opacity on Optical Coherence Tomography Angiography Metrics

PURPOSE To evaluate the impact of lens opacity on the reliability of optical coherence tomography angiography metrics and to find a vessel caliber threshold that is reproducible in cataract patients. METHODS A prospective cohort study of 31 patients, examining one eye per patient, by applying 3 × 3 mm macular optical coherence tomography angiography before (18.94 ± 12.22 days) and 3 months (111 ± 23.45 days) after uncomplicated cataract surgery. We extracted superficial (SVC) and deep vascular plexuses (DVC) for further analysis and evaluated changes in image contrast, vessel metrics (perfusion density, flow deficit and vessel-diameter index) and foveal avascular area (FAZ). RESULTS After surgery, the blood flow signal in smaller capillaries was enhanced as image contrast improved. Signal strength correlated to average lens density defined by objective measurement in Scheimpflug images (Pearson's r: -.40, p: .027) and to flow deficit (r= -.70, p < .001). Perfusion density correlated to the signal strength index (r = .70, p < .001). Vessel metrics and FAZ area, except for FAZ area in DVC, were significantly different after cataract surgery, but the mean change was approximately 3-6%. A stepwise approach in extracting vessels according to their pixel caliber showed a threshold of > 6 pixels caliber (∼20-30 µm) was comparable before and after lens removal. CONCLUSION In patients with cataract, OCTA vessel metrics should be interpreted with caution. In addition to signal strength, contrast and pixel properties can serve as supplementary quality metrics to improve the interpretation of OCTA metrics. Vessels with ∼20-30 µm in caliber seem to be reproducible.