Choriocapillaris Imaging Using Multiple En Face Optical Coherence Tomography Angiography Image Averaging

Abstract

Imaging of the choriocapillaris in vivo is challenging with existing technology. Optical coherence tomography angiography (OCTA), if optimized, could make the imaging less challenging.OBJECTIVE To investigate multiple en face image averaging on OCTA images of the choriocapillaris.DESIGN, SETTING, AND PARTICIPANTS Observational, cross-sectional case series at a referral institutional practice in Los Angeles, California. From the original cohort of 21 healthy individuals, 17 normal eyes of 17 participants were included in the study. The study dates were August to September 2016.EXPOSURES All participants underwent OCTA imaging of the macula covering a 3 × 3-mm area using OCTA software (Cirrus 5000 with AngioPlex; Carl Zeiss Meditec). One eye per participant was repeatedly imaged to obtain 9 OCTA cube scan sets. Registration was first performed using superficial capillary plexus images, and this transformation was then applied to the choriocapillaris images. The 9 registered choriocapillaris images were then averaged. Quantitative parameters were measured on binarized OCTA images and compared with the unaveraged OCTA images. MAIN OUTCOME AND MEASURE Vessel caliber measurement.RESULTS Seventeen eyes of 17 participants (mean [SD] age, 35.1 [6.0] years; 9 [53%] female; and 9 [53%] of white race/ethnicity) with sufficient image quality were included in this analysis. The single unaveraged images demonstrated a granular appearance, and the vascular pattern was difficult to discern. After averaging, en face choriocapillaris images showed a meshwork appearance. The mean (SD) diameter of the vessels was 22.8 (5.8) μm (range, 9.6-40.2 μm). Compared with the single unaveraged images, the averaged images showed more flow voids (1423( flow voids [95% CI, 967-1909 vs 1254 flow voids [95% CI, 825-1683], P < .001), smaller average size of the flow voids (911 [95% CI, 301-1521] μm 2 vs 1364 [95% CI, 645-2083] μm 2 , P < .001), and greater vessel density (70.7% [95% CI, 61.9%-79.5%] vs 61.9% [95% CI, 56.0%-67.8%], P < .001). The distribution of the number vs sizes of the flow voids was skewed in both unaveraged and averaged images. A linear log-log plot of the distribution showed a more homogeneous distribution in the averaged images compared with the unaveraged images.CONCLUSIONS AND RELEVANCE Multiple en face averaging can improve visualization of the choriocapillaris on OCTA images, transforming the images from a granular appearance to a level where the intervascular spaces can be resolved in healthy volunteers.

Conjunctival and Intrascleral Vasculatures Assessed Using Anterior Segment Optical Coherence Tomography Angiography in Normal Eyes

“…26, 27, 29 Vessel diameter index, which represents the average vessel caliber, was calculated by dividing the total vessel area in the binarized image (shown in Supplemental Figure 1, Middle) by the total vessel length in the skeletonized image (shown in Supplemental Figure 1, Right). 21, 27 Fractal dimension was calculated on the skeletonized image using ImageJ plugin software. 27, 30 The box-counting method was used for calculation.…”

“…Previous studies have investigated the vessels of the posterior eye segments, such as the optic nerve head, retina, and choroid. 17–21 Although a few OCTA studies have investigated the vessels of the anterior segment (AS), such as the iris and cornea, 22–25 the potential of AS-OCTA has not been fully explored. AS-OCTA is supposed to be useful for various types of ocular or systemic diseases, including ocular-surface disorders and glaucoma, if it can assess the conjunctival and scleral vessels qualitatively and quantitatively.…”

Optical Coherence Tomography Angiography Offers New Insights into Choriocapillaris Perfusion

“…Recently, Uji et al [36] presented a multiple en face averaging approach in healthy volunteers that markedly improves CC visualization on OCTA images, transforming the images from a granular appearance to a level where the intervascular spaces can be resolved. The morphologic patterns seen in averaged CC images closely mimic the meshwork pattern observed on CC histology.…”

OCT Angiography (OCTA) in Retinal Diagnostics

“…These parameters are suitable for capturing dropout of vasculature that occurs in diseases like diabetic retinopathy, retinal vein occlusion or glaucoma [17][18][19][20]. A quantification of flow void area is also possible, for instance for assessing the choriocapillaris structure [21]. Besides vessel density, other parameters that summarize morphological features of vessel branches and vessel network structure, including complexity measures such as vessel tortuosity, fractal dimension, or branching point densities and vessel diameter statistics, are in common use [17-19, 22, 23].…”