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Justin Migacz, Robert Zawadzki, Ravi Jonnal, John Werner; Ultrahigh-speed OCTA imaging of the choriocapillaris around drusen at 1.6 MHz. Invest. Ophthalmol. Vis. Sci. 2019;60(11):004. doi: https://doi.org/.
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The choriocapillaris (CC) vasculature may play significant role in the progression of age-related macular degeneration (AMD). Our recently-developed ultrahigh-speed OCT angiography (OCTA) system enables the clear in-vivo visualization of CC vasculature throughout the whole macula. To gain a better understanding of the role of the CC, we imaged healthy and diseased subjects and characterized the appearance of the CC in areas around and far from drusen.
We performed OCTA imaging on 13 eyes of 10 subjects with AMD. The average age was 68.6 ± 9.5 years. We also imaged 7 eyes of 7 young subjects (34 ± 15 years), and 7 eyes of 5 age-matched normals (74 ± 3.7 years). OCT imaging was performed with a custom swept-source OCT system operating at 1.64 MHz. Between 9 and 16 volumetric scans, lasting 2 seconds each, were performed on all subjects at locations ranging from the fovea to 12 degrees away. The field of view was either 1.2 or 1.5 mm. The Fourier-transform of each CC image was computed, and the dominant frequency was recorded as indicating the average vessel period in the image, a proxy for vessel density.
CC vessel spacing was slightly smaller (38.4 ± 3.6 μm) in normal than in those with AMD (39.5 ± 4.5 μm) and increased slightly with age (0.4 μm per decade). Fig. 1 shows the spatial frequency data as a function of age and foveal eccentricity, where the size of the bubble indicates the vessel density (#/mm). Fig. 2 shows the angiography of one normal (top two panels) and one representative AMD subject (remaining panels). CC vessels near the fovea of the normal indicate a large gap in the vasculature, which may be a so-called “flow void.” In the subject with AMD, an OCT B-scan of drusen is shown (left middle). The adjacent panel (right middle) of the OCT projection of the RPE layer indicates where drusen are present. Below (bottom right) the OCTA angiogram of the CC layer indicates that there are many areas of reduced flow (dropout) including in areas away from drusen. The corresponding reflectance OCT (left bottom) CC image is shown. There is some shadowing in this layer. Shadowing does not account for the reduced OCTA signal, so dropout areas are likely caused by lower flow.
The ultrahigh speed system is effective for imaging the CC layer in subjects with drusen. Dropout exists where drusen are absent, suggesting that dropout may precede the appearance of drusen in these subjects.
This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.
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