Abstract
Purpose :
To assess the influence of varying B-scan frame sampling densities on retinal thickness and volume measurements from spectral domain optical coherence tomography (OCT) in eyes with neovascular age-related macular degeneration (AMD).
Methods :
Volume OCT data (512x128 macular cube over 6x6 mm) were collected from 30 eyes with neovascular AMD. Manual segmentation of all 128 B-scans in each image set was performed allowing quantification of the neurosensory retina, subretinal fluid (SRF), subretinal hyper-reflective material (SRHM), and pigment epithelium detachment (PED). Thickness maps were then generated for less dense subsets of scans, ranging from every other (64 B-scans) to every 32nd (4 B-scans). For each less dense subset, foveal central subfield (FCS) thickness and total macular volume (TMV) were compared with values obtained using all 128 scans (considered the reference).
Results :
For each parameter, the mean absolute difference compared to the reference did increase with decreasing B-scan density. However these differences did not reach statistical significance (p<0.05) until B-scan density was reduced to every eighth scan (i.e., 16 B-scans spaced 375 µm apart) for neurosensory retina and every fourth scan (i.e., 32 B-scans spaced 188 µm apart) for SRF, SRHM and PED . Using only 16 B-scans, for neurosensory retina, the mean (% error) and maximum (% error) absolute differences in TMV, were 0.02 mm3 (0.24%) and 0.06 mm3 (0.79%), respectively. Similarly, using only 32 B-scans, mean and maximum difference in volumes for SRF were 0.01 mm3 (3.50%) and 0.03 mm3 (20%). The mean difference in volume for SRHM and PED were 0.01 mm3 and 0.01 mm3 respectively.
Conclusions :
A minimum of 16 equally spaced B-scans, covering a 6 x 6 mm area, appears necessary to generate retinal thickness measurements similar to those using all 128 B-scans in eyes with choroidal neovascularization. For other components related to the CNV lesion (SRF, SRHM, PED), however, 32 B-scans over this same area are required. These results may have implications for designing acquisition and grading protocols for clinical studies using OCT in neovascular AMD.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.