Influence of scanning density on macular choroidal volume measurement using spectral-domain optical coherence tomography

Background To evaluate the impact of scanning density on macular choroidal volume measurement using spectraldomain optical coherence tomography (SD-OCT). Methods Thirty eyes of normal subjects underwent consecutive raster choroidal scanning protocols using SD-OCT in enhanced-depth imaging mode. Manual choroidal segmentation was performed using the built-in automated retinal segmentation software to obtain five analyses with different interscan distances, including inter-scan distances of 30 μm, 60 μm, 120 μm, 240 μm, and 480 μm. The built-in software of the device automatically generated the choroidal thickness and volume map in the similar manner as for the retinal volume map, using the standardized Early Treatment Diabetic Retinopathy Study (ETDRS) grid. For each raster scan, mean absolute difference and relative difference of mean foveal choroidal thickness (FCT), foveal choroidal volume (FCV) and total macular choroidal volume (TCV) in comparison to "true value" (i.e., 30-μm inter-scan distance) were calculated. Results The maximum relative differences were 10 % and 16 % for TCV and FCV respectively. For mean FCT, the maximum absolute difference was 31 μm, and maximum relative difference was 12.7 %. No statistically significant differences were found in measurements of mean foveal choroidal thickness (p=0.912) and volume (p=0.944), as well as macular choroidal volume (p=0.912), with varying inter-scan distance. Conclusions Our study shows that approximately 16 scans over the macula with a inter-scan distance of 480 μm is sufficient to provide a clinically relevant and reliable choroidal thickness/volume map. This information could be useful in the design of choroidal scanning protocols for future clinical trials.