Parafoveal vessel density has been reported for regions resembling our ROI-250 and ROI-500 in previous studies. For example, using an adaptive optics scanning laser ophthalmoscope, Tam et al.
10 found an average vessel density of 31.6 mm
−1 (
N = 10) in the inner region. In addition, using a high-resolution, wide-field dual-conjugate adaptive optics instrument, Popovic et al.
13 found a mean capillary density of 38.0 mm
−1 in the inner ROI, and 36.4 mm
−1 in the outer ROI (
N = 5). In both studies, measurements were corrected for ocular magnification. In a histologic study, Mendis et al.
4 found a mean vessel density of 41.1% in the superficial and 23.0% in the deep capillary network in confocal microscopy (
N = 5). The specimens, however, were taken at 850 to 2150 μm eccentricity from the foveal center. With FA, they found a mean vessel density of 24.4% in the same location (
N = 10).
4 To convert their numbers to measures similar to those used by Tam et al.
10 and Popovic et al.
13, we could assume a capillary width of 7 μm. Their “capillary percent area” yields an area measurement that can be divided by capillary width to obtain total capillary length. Dividing total capillary length by the area of the ROI yields a metric that can be compared to other studies. Applying this algorithm, the measurements of Mendis et al.
4 convert to 58.6 and 32.9 mm
−1 in the superficial and deep layer by confocal microscopy, and 34.3 mm
−1 by FA. Our measures can be similarly converted using an estimated capillary width of 15 μm to account for the apparent wider appearance of capillaries on OCT imaging. On our first assessment of the data, based on multiple measurements of the parafoveal capillaries in several images/cases, the average width appeared to be 15 μm, which corresponds to the transverse resolution of the SS-OCT system. Thus, based on the optical limitations, the use of an estimated capillary width of 15 μm for our study appears appropriate. Using this assumption, our mean capillary density in the SRL converts to 44.9 mm
−1 in the ROI-250 and 49.5 mm
−1 in the ROI-500. In the DRL, the mean capillary density converts to 23.0 mm
−1 in the ROI-250 and 48.2 mm
−1 in the ROI-500. When compared to the results of Tam et al.
10 and Popovic et al.,
13 our estimated vessel density is higher. This is most likely due to the different vessel extraction technique: Tam et al.
10 outlined the centerlines of the vessels, and Popovic et al.
13 skeletonized the vessel signature to a 1 pixel–wide tracing. In this study, the extracted vessel signature was not skeletonized as shown in
Figure 2. When compared to the results of Mendis et al.,
4 our estimated vessel density is lower for the superficial inner retinal layer. This was expected as the specimens of Mendis et al
4 were taken at a greater eccentricity. Recently, Chui et al.
21 used adaptive optics scanning laser ophthalmoscope imaging to study the relationship between the thickness of the retina and size of FAZ, and suggested that the inner retinal circulation might be required to support a retinal thickness greater than 60 μm.
21 It would be interesting in the future with a larger cohort to determine whether a similar relationship could be established between retinal thickness and the OMAG determined FAZ.