Abstract
Purpose :
The purpose of the study was to identify new contrast mechanisms that reveal retinal structures not visible with other methods and would enable improved understanding of retinal pathology manifested in disruption of the vasculature.
Methods :
Offset imaging provides cellular-level visualization of retinal structures with unprecedented details not available with other imaging modalities; however, directionality artifacts impede interpretation of individual offset images. Multi-channels offset AO-SLO provides isotropic images of retinal structures free of directionality artifacts. The PSI adaptive-optics retinal imager (MAORI) uses a fiber bundle arrangement that enables simultaneous collection of four offset images. Split-detection combining pairs of offset images is interpreted as phase derivative; the magnitude of phase gradient (MPG) is calculated from pairs of orthogonal split images.
Results :
Two orthogonal split images highlight structural edges such as blood vessel walls along different directions making MPG isotropic. The mean of the standard deviation (STD) from multiple split images isotropically highlights the blood flow. Segmentation of MPG and STD images enables quantification of blood vessels walls geometric characteristics such as the lumen (LD) and vessel (VD) diameter, and wall-to-lumen ratio (WLR) along the length of the vessel (panel A). In addition, in particular in eyes with pathology, disruptions of the vessel wall structural integrity can be visualized in MPG images as highlighted by white arrows in panels B and C. Bulging or local thinning of walls may become the location of future microaneurysms. Panel A shows strong continuous vessel borders for a healthy subject, in contrast to the multiple wall disruptions (panels B and C) for subjects with type 1 diabetes but no diabetic retinopathy. Additional examples will be shown at the meeting.
Conclusions :
AO-SLO imaging based on simultaneous acquisition of four offset aperture images provides an improved, isotropic, free of directionality artifacts, image of the inner retina vasculature. Phase gradient and motion contrast enable segmentation of the blood vessel wall and quantification of its geometric characteristics as well as identification of vessel wall integrity disruptions, all of which have diagnostic value.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.