Enhanced retinal vascular microstructure in flood illuminated adaptive optics ophthalmoscopy

Abstract

Purpose : Non-invasive imaging of the retinal microvasculature remains challenging. Offset aperture imaging in adaptive optics scanning light ophthalmoscopy (AOSLO) has revealed the fine structure of retinal vessels including blood vessel walls (Chui et al. 2012). It has been hypothesized that contrast enhancement in offset aperture arises from the detection of multiply scattered light. To date, such contrast enhancement has not been demonstrated using flood illuminated adaptive optics ophthalmoscopy (FIAO). Here we tested the hypothesis that forward scatter in the region of the lamina cribrosa (LC) can be capitalized on to obtain similar enhancement of the microvasculature in FIAO.

Methods : Images of vascular regions of interest (2.4°×2.4° field of view) near the optic nerve head were obtained in five healthy subjects (ages: 24–45; 4 men and 1 woman) without pupil dilation. Images were acquired at 200 Hz using a FIAO prototype built at the Quinze-Vingt National Ophthalmology Hospital. Image sequences (10 seconds; 2000 images) were registered and averaged and error maps calculated.

Results : In the region of the LC, a strong reflection from the LC backlights the vessels, acting as a source for forward scatter imaging. Here we obtained structural images of second order arteries (~90 micron diameter) that revealed several layers of mural cells. Images were similar in appearance to AOSLO offset aperture images of an artery of similar size reported in the literature (Chui et al. 2012). In some images, both forward and backscattering signals were visible simultaneously in different zones of the image. Red blood cells were revealed with substantially higher contrast in the forward scattering zones.

Conclusions : Preliminary results tend to confirm the hypothesis that the structural resolution enhancement of retinal vessels obtained with the offset aperture method in AOSLO could be achieved with FIAO in the region of the LC. Furthermore, it suggests that the main effect of shifting detection away from the optical axis in confocal AOSLO is to select for light that is more forward scattered.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.