Imaging vascular pathologies in the chorioretinal complex by phase-variance SSOCT system with real-time retinal motion correction with an SLO

Abstract

 

Purpose

 

A phase-variance contrast optical coherence tomography (pvOCT) system was combined with a video-rate scanning laser ophthalmoscope (SLO) to correct eye motion of subjects. The system was used to collect motion-corrected OCT volume mosaics of subjects with age-related macular degeneration (AMD) and the data were analyzed for phase-variance contrast to reveal the vasculature. A comparison of vascular maps with and without motion correction are presented. The maps were also compared with fluorescein angiography (FA) images.

 

Methods

 

Six subjects were imaged with the joint OCT and tracking SLO system, including three subjects with age-related macular degeneration (AMD) and three with no known pathology. The OCT light source was a swept-source laser operating at 1060 nm with a sweep repetition rate of 100 kHz. The optical power of the OCT light beam on the cornea was 1.4 mW. The system provided axial resolution of 5.4 µm in tissue. Phase variance data were calculated from sets of 5 B-scans acquired at each location in the volume. These data highlight the flow of blood cells. Scanning areas were 1x1 mm² _­­and multiple locations were imaged during each imaging session. The SLO system tracked the motion in a 1.5x1.5 mm² region of the retina with a 0.4mW beam. Motion of the SLO images was tracked in real-time to adjust the OCT scanner position, thus allowing the system to follow eye movements.

 

Results

 

The vascular images of subjects had a noticeable reduction in motion artifacts when motion tracking was activated. Figure 1 shows a comparison of the OCT imaging with and without tracking. The top panel shows a representative OCT intensity B-scan from a subject with no pathology. The subsequent images show the pvOCT processed en-face projections of the inner retinal capillaries and choriocapillaris. Retinal capillaries appear to have fewer discontinuities when tracking is activated, although it cannot correct for large saccades. Fluorescein angiography images of the same retinal locations show vascular patterns that agree well with those captured with pvOCT, validating the accuracy of the system (Figure 2).

 

Conclusions

 

The combination of OCT with a tracking SLO is a complex system and requires careful alignment and calibration. The improvement in image quality, however, is significant when compared to standard OCT systems and standard clinical tools such as FA.