Single shot wide field MHz swept source optical coherence tomography angiography

Abstract

Purpose : Several retinal diseases show vascular pathologies in the periphery first. Although widefield fluorescein angiography (FA) fundus cameras can image these areas, they require contrast agents and a lengthy patient setup procedure. In this work, we present how MHz swept-source OCT angiography (SS-OCTA) can provide similar information non-invasively and faster.

Methods : We developed a SS-OCTA system using a frequency-domain mode locked laser operating at an A-scan rate of 1.7 MHz with a central wavelength of 1060 nm and a tuning range of 75 nm, translating to 9 µm axial resolution in tissue. The lateral resolution is 20 µm (1/e²) and the imaging depth in tissue is 6 mm. To compensate for eye motion, the retina is tracked during acquisition using an additional line scanning ophthalmoscope. If motion occurs, the scan location is corrected, and the scans acquired since motion detection are rescanned. The single shot field of view (FOV) of 18 mm by 18 mm (~65 degrees) on the retina is sampled laterally with 2048x2048 A-scans and 4 repetitions per slow scanning axis position. After SS-OCTA processing using the complex signal, projections from the inner limiting membrane to the IS/OS junction are generated. In this study, we imaged 5 healthy subjects, and 20 patients with diabetic retinopathy, choroidal neovascularization, and retinal occlusion.

Results : We acquired single shot SS-OCTA images with a FOV of 65 degrees from healthy subjects and patients with retinal diseases. The acquisition time with tracking enabled was well below 30s in patients. The image quality was sufficient to resolve capillaries over the entire FOV. Figure 1 shows the widefield SS-OCTA projection of a diabetic eye. SS-OCTA’s motion contrast allows for identification of areas of non-perfusion. Because the full level of detail cannot be appreciated in the widefield image as displayed in Fig. 1, Fig. 2 shows magnified views of the same acquisition at the locations indicated by the orange boxes. In Fig. 2II), even the capillaries around the foveal avascular zone can be resolved.

Conclusions : We demonstrated that SS-OCTA is approaching the FOV of widefield FA fundus cameras. This has reduced chair time and lack of need for contrast agents, which makes widefield SS-OCTA a potential replacement for many FA exams.

This is a 2021 ARVO Annual Meeting abstract.

 

Fig 1. Widefield SS-OCTA image of a diabetic patient

 

Fig 2. Magnifications of the areas indicated in Fig. 1