Abstract
Purpose :
Retinal perfusion in and near the foveal avascular zone (FAZ) depends upon sparse capillaries organized into plexuses, mapped with optical coherence tomography (OCT) and OCT angiography (OCTA), and reflective and variance mapping using adaptive optics scanning laser ophthalmoscopy (AOSLO). These differ in contrast generation methods and spatial and temporal sampling. We hypothesized that our previous finding of vessel remodeling on AOSLO in diabetic patients without measurable thickening on OCT is consistent with vascular changes dominated by small or tortuous vessels or slow blood flow.
Methods :
Data were compared for OCTA and AOSLO for 10 diabetic patients and 12 age-similar controls. To give the best chance to see small features, we selected diabetic datasets with sufficient optical media quality and fixation stability for cone counting. One eye of each participant was imaged to provide en face SLO, SD-OCT, and OCT-A (Heidelberg Spectralis II, Heidelberg Engineering, Heidelberg, Germany). For AOSLO, 100 frames were digitized using 30 Hz aberration corrections. Averages and variance maps were computed for retinal vessels. Confocal images were collected at 769 nm with an aperture of about 4.2 microns for an emmetropic eye. Simultaneous multiply scattered light images for variance maps at 769 and 842 nm had apertures of 21 microns, displaced 15 microns. AOSLO images collected at 29 Hz produced retinal images of 780 x 520 pixels, with 1.9° x 1.6° (WxH) the lowest resolution used. AOSLO en face digital resolution was 4x that of OCTA. En face OCTA images were enlarged via upsampling, colorized, and aligned with AOSLO images.
Results :
The OCTA intermediate capillary plexus slab produced the clearest and smallest FAZ vessel map in all 10 patients, minimizing projection artifacts. Capillary distortion and tortuosity, and smaller microaneurysms and vessel loops, seen on AOSLO (Fig. 1) were spatially correlated with OCTA (Fig. 2), despite less detectable and noise degrading vessel fine structure, indicating the small OCTA features had a vascular origin, not random noise.
Conclusions :
Both AOSLO and OCTA showed vessel remodeling dominated by small vessels of distorted shapes and features, usually clearer on AOSLO. Improved spatial resolution for OCTA would improve detection of these small, but possibly critical, features.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.