The instrument used in this study was a SS-OCTA system (PLEX Elite 9000, Carl Zeiss Meditec, Inc.), running at 100 kHz, that is 100,000 A-scans per second. This instrument is characterized by a central wavelength of 1060 nm, a bandwidth of 100 nm, an A-scan depth of 3.0 mm in tissue, a full-width at half maximal (FWHM) axial resolution of ∼5 μm in tissue, and a lateral resolution at the retinal surface estimated at ∼12 μm. FastTrac motion correction software (Carl Zeiss Meditec, Inc.) was used while the images were acquired. A scan with a nominal field of view (FoV) of 3 × 3 mm (equivalent to an angular view of 10.47 × 10.47 degrees measured in air at the pupil plane) centered on fovea was acquired on all the subjects. The scan contained 300 A-lines × 300 locations with four repeated scans in each fixed location. The complex optical microangiography (OMAGc) algorithm was used to obtain OCTA images. This algorithm utilizes the variations in both the intensity and phase information between sequential B-scans at the same location to generate the motion signal, which indicates blood flow.18 (link) A validated semiautomated segmentation algorithm was applied to identify relevant retinal layers,29 (link) and manual corrections were carried out as necessary to ensure accurate segmentation. In particular, we evaluated en face angiograms of the choriocapillaris slab, which was defined by a layer starting at the outer boundary of BM and ending at approximately 20 μm beneath BM. A maximum projection was applied on the segmented volumes to generate the en face angiograms. Images were excluded from the study if significant media opacity was present, if signal strength was less than seven as defined by manufacturer, which prevented high-quality imaging, if there was severe motion artifact, or if any other macular pathology was present except drusen.
OCTA scans with nominal 3 × 3 mm pattern were also acquired approximately 9 mm inferior-nasal, and 12 mm temporal to the central fovea to facilitate qualitative comparison with characteristic scanning electron microscopic images as a function of distance from the fovea.
OCTA scans with nominal 3 × 3 mm pattern were also acquired approximately 9 mm inferior-nasal, and 12 mm temporal to the central fovea to facilitate qualitative comparison with characteristic scanning electron microscopic images as a function of distance from the fovea.
