Impact of image averaging on vessel detection using optical coherence tomography angiography in eyes with macular oedema and in healthy eyes.

PURPOSE: To assess the repeatability of multiple automatic vessel density (VD) measurements and the effect of image averaging on vessel detection by optical coherence tomography angiography (OCTA). METHODS: An observational study was conducted in a series of healthy volunteers and patients with macular oedema. Five sequential OCTA images were acquired for each eye using the OptoVue HD device. The effect of the averaging of the 5 acquisitions on vessel detection was analysed quantitatively using a pixel-by-pixel automated analysis. In addition, two independent retina experts qualitatively assessed the change in vessel detection in averaged images segmented in 9 boxes and compared to the first non-averaged image. RESULTS: The automatic VD measurement in OCTA images showed a good repeatability with an overall mean intra-class correlation coefficient (ICC) of 0.924. The mean ICC was higher in healthy eyes compared to eyes with macular oedema (0.877 versus 0.960; p < 0.001) and in the superficial vascular plexus versus the deep vascular complex (0.967 versus 0.888; p = 0.001). The quantitative analysis of the effect of the averaging showed that averaged images had a mean gain of 790.4 pixels/box, located around or completing interruptions in the vessel walls, and a mean loss of 727.2 pixels/box. The qualitative analysis of the averaged images showed that 99.6% of boxes in the averaged images had a gain in vessel detection (i.e., vessels detected in the averaged image but not in the non-averaged image). The loss of pixels was due to a reduction in background noise and motion artifacts in all cases and no case of loss of vessel detection was observed. CONCLUSION: The automatic VD measurement using the OptoVue HD device showed a good repeatability in 5 acquisitions in a row setting. Averaging images increased vessel detection, and in about a third of boxes, decreased the background noise, both in healthy eyes and, in a greater proportion, in eyes with macular oedema.

ACUTE PSEUDOPHAKIC CYSTOID MACULAR EDEMA IMAGED BY OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

PURPOSE: To study macular capillary changes and vessel density in acute pseudophakic cystoid macular edema (PCME) before and after treatment using optical coherence tomography angiography. METHODS: Retrospective observational case-control study of seven consecutive patients (eight eyes) with PCME and eight age-matched control eyes imaged with optical coherence tomography angiography (RTVue XR Avanti; Optovue, Inc, Fremont, CA) using Projection Removal Artifacts software. Vessel density was calculated. RESULTS: The mean time to diagnosis of PCME was 2.3 ± 0.9 months after surgery. At initial examination, the superficial capillary plexus pattern was near-normal in all PCME eyes, although it was attenuated in the deep capillary plexus. The mean vessel density of the superficial capillary plexus in PCME eyes was slightly but significantly lower than in control eyes (47.8 ± 3.8% vs. 52.9 ± 4.0%, P = 0.01), the difference being greater in the deep capillary plexus (44.1 ± 7.4% vs. 54.2 ± 3.2%, P = 0.007). After resolution of the edema, the deep capillary plexus completely recovered its normal pattern and the vessel density in both plexuses was no longer different from that observed in control eyes. CONCLUSION: Macular vessel density after resolution of an acute PCME did not differ from that of normal control eyes in both the superficial capillary plexus and deep capillary plexus, unlike macular edema in retinal vaso-occlusive diseases.