Blood Flow in Retinal Micro Vessels

Abstract

Abstract: : Purpose: Visualization of the blood flow in micro vessels (10 µm diameter) of the retina by means of adaptive optics. Methods: Recordings of flood images of the retina using adaptive optics now enable capture of high resolution images of the photoreceptors mosaic at a frame rate of 7 Hz. Despite the random motion of the field of view, due to the ocular drifts, an accurate XY registration of the successive images is possible, thanks to the high SNR that AO now provides to in vivo imaging, and the absence of field distorsion, which are two advantages compared to conventional scanning techniques. Several series of AO assisted very short integration images (7ms) have been obtained on 3 subjects at about 3º excentricities. The time interval between frames is 150 ms, and the total duration of an examination is 6sec (40 frames). The observing wavelength is 550 nm. The spatial resolution is better than 2 µm. Results: At 3º excentricity, all images clearly reveal the photoreceptor mosaic and the overlying micro vascularization. Offline spatial cross correlation between images permits a registration at a submicron accuracy and the reconstruction of short moving sequences are possible. Temporal analysis of post–processing centred images, points out a strong variation of the reflected signal in the shadow of the overlying micro vessel (10 µm diameter), corresponding to the transit of the red cells. We use this variation as an indicator of the flow activity and propose an original way to map the circulatory activity, in the living eye. The statistical analysis of these sequences, such as the rms variation of the signal at each point, can be used as an evaluation of the blood flow. Conclusions: Direct flood imaging associated with AO provides high resolution images with a high frame rate. These two improvements allow a direct observation of the blood flow in micro–vessels and a in situ and vivo analysis of the micro vascularization of the retina.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)