Abstract
Purpose :
Imaging the peripheral retina using optical coherence tomographic angiography (OCTA) has generated serious interest in evaluating retinal vascular diseases, particularly in early stages of diabetic retinopathy. However, the field of view (FOV) of current OCTA is severely limited by A-line rates and inefficient scanning protocols with unnecessary fly-back A-lines. Here, we report a wide-field OCTA system that can acquire a 60-degree FOV in 6 seconds without resorting to montaging.
Methods :
The OCT system utilizes an AXSUN 400kHz dual swept source laser system with a center wavelength of 1060nm and 100nm bandwidth. The scanning lens system consists of two 2-inch 200mm and two 2-inch 100 mm achromatic doublets lenses. We designed the sample arm using computer-aided design (CAD) software and built it using 3D printed optical mounts. We achieve axial and transverse resolutions of 5.5 and 19 µm, respectively, with a total imaging depth of 4.2mm. The laser power on the pupil was set to be 2mW using a variable attenuator. A bidirectional scanning protocol with zero fly-back was applied during image acquisition to maximize the scanning efficiency (Fig. 1). Split-spectrum amplitude-decorrelation angiography (SSADA) was used to construct the OCTA volume. En face reflectance maps of the inner retina are generated by mean projection of structural OCT signals within the segmented inner retinal slab; en face angiograms of the inner retina are produced by mean decorrelation (flow) projection within the same slab.
Results :
The sensitivity of this OCT system was measured as 120dB. To test the system, we imaged the retina of seven healthy human eyes. Each scan volume contains 768 B-scans, and each B-scan contains 1536 A-lines, with two repeated B-scans acquired at each location to generate OCTA signals. We show OCT and OCTA images with a 60 degree of FOV (18 × 18 mm) can provide clinically acceptable image quality (Fig. 2). Details of the inner retinal microvasculature can be clearly appreciated by this one-shot single-volume wide-field angiogram. Due to the short scanning time, the OCTA image shows few motion artifacts even with such a large FOV.
Conclusions :
We successfully acquired a single-volume wide-field OCTA image with 60-degree FOV. We achieved a total scan time of 6 seconds using a 400-kHz swept source laser and an efficient bidirectional scanning protocol.
This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.