Ultrahigh-Speed, Swept-Source Optical Coherence Tomography Angiography in Nonexudative Age-Related Macular Degeneration with Geographic Atrophy

Abstract

PURPOSE To investigate ultrahigh speed, swept source optical coherence tomography (SSOCT) angiography for visualizing vascular changes in eyes with non-exudative age-related macular degeneration (AMD) with geographic atrophy (GA). DESIGN Observational, prospective, cross-sectional study. PARTICIPANTS A total of 63 eyes from 32 normal subjects and 12 eyes from 7 patients with non-exudative AMD with GA. METHODS A 1050 nm, 400 kHz A-scan rate SSOCT system was used to perform volumetric optical coherence tomography angiography (OCTA) of the retinal and choriocapillaris (CC) vasculatures in normal subjects and patients with non-exudative AMD with GA. OCTA using variable interscan time analysis (VISTA) was performed to assess CC alteration and differentiate varying degrees of CC flow impairment. MAIN OUTCOME MEASURES Qualitative comparison of retinal and CC vasculatures in normal subjects versus those in patients with a clinical diagnosis of non-exudative AMD with GA. RESULTS In all 12 eyes with GA, OCTA showed pronounced CC flow impairment within the region of GA. In 10 of the 12 eyes with GA, OCTA with VISTA showed milder CC flow impairment extending beyond the margin of GA. Of the 5 eyes exhibiting foveal sparing GA, OCTA showed CC flow within the region of foveal sparing in 4 of the eyes. CONCLUSIONS The ability of ultrahigh speed, swept source OCTA to visualize alterations in the retinal and CC vasculatures noninvasively makes it a promising tool for assessing non-exudative AMD with GA. OCTA using VISTA can distinguish varying degrees of CC alteration and flow impairment and may be useful for elucidating disease pathogenesis, progression, and response to therapy.

Optical Coherence Tomography Angiography Offers New Insights into Choriocapillaris Perfusion

“…This can produce artifacts, but allows for a more robust visualization of vasculature [26]. The exact localization and thickness of the CC slab vary between 0 and 34 µm below the RPE/Bruch's membrane reference and between 4.4 and 30 µm, respectively, depending on the device used [17,20,27,28]. Notably, manufacturers use various definitions of the CC slab level, and not all of them offer a presetting for CC examination yet (Table 1).…”

“…However, by doing so, OCTA also becomes more sensitive to eye motion, which increases artifact image noise [30]. An interesting approach is the variable interscan time analysis (VISTA) algorithm which was firstly described by Choi and colleagues [27,31], a tool that allows for distinguishing varying degrees of CC flow impairment. Notably, this method provides a relative blood flow measurement and is only applicable to slow flows of <0.3 mm/s.…”

Regression-based algorithm for bulk motion subtraction in optical coherence tomography angiography

“…To obtain flow signal, OCTA algorithms [1,3,[18][19][20] rely on mathematical operations that quantify variations in the amplitude and/or the phase of optical coherence tomography (OCT) signal between at least two consecutive B-scans acquired at the same raster position. However, since the interscan time cannot be extremely small without affecting sensitivity to slow-speed blood flow [21,22], OCTA of the retina is sensitive to involuntary eye motion between B-scans.…”

Automated motion correction using parallel-strip registration for wide-field en face OCT angiogram

“…Considering the optimal time delay between B-frames is around 3-5 ms for OCTA of capillary blood flow [22], the number of A-lines within each B-frame would be higher (600-1000 or higher) than the number of B-frames (<600) that could be accommodated by a comfortable scan time of less than 4 seconds. Therefore, a non-orthogonal scanning and registration scheme would be more efficient.…”