Real-time eye motion compensation for OCT imaging with tracking SLO

Abstract

Fixational eye movements remain a major cause of artifacts in optical coherence tomography (OCT) images despite the increases in acquisition speeds. One approach to eliminate the eye motion is to stabilize the ophthalmic imaging system in real-time. This paper describes and quantifies the performance of a tracking OCT system, which combines a phase-stabilized optical frequency domain imaging (OFDI) system and an eye tracking scanning laser ophthalmoscope (TSLO). We show that active eye tracking minimizes artifacts caused by eye drift and micro saccades. The remaining tracking lock failures caused by blinks and large saccades generate a trigger signal which signals the OCT system to rescan corrupted B-scans. Residual motion artifacts in the OCT B-scans are reduced to 0.32 minutes of arc (~1.6 µm) in an in vivo human eye enabling acquisition of high quality images from the optic nerve head and lamina cribrosa pore structure.

Optical coherence tomography imaging in uveitis

“…In the Spectralis system, the retinal image (1,000 points) from the infra-red SLO imaging channel is used to track motion. In the RTVue system the motion is measured at 30 Hz from an infrared fullfield fundus camera [17,18]. The Cirrus system reduces eye motion artifacts with a proprietary scan acquisition strategy, a high-speed 20 Hz line scanning ophthalmoscope (LSO) camera, and single-pass alignment scanning.…”

Digital micromirror device based ophthalmoscope with concentric circle scanning

“…It could be possible to extract motion information and use this to track the eye's movement. When done fast enough, it will also enable doing eye motion correction in real-time [32,33] to improve the quality of the images by averaging multiple images at the same location and correct for the minor motion artefacts present in these images. Image registration could potentially be better with the parallel illumination as all the illumination points of a single frame are undistorted.…”

Active eye-tracking for an adaptive optics scanning laser ophthalmoscope

“…The product of the degrees/pixel in the TSLO and the volts/degree calculated from the AOSLO is the needed voltage/pixel conversion to generate the 14-bit signal for the FPGA. Analog gain amplification is then used to scale the voltage signal sent from the FPGA to match the range of that required by the tip/tilt mirror [21]. Due to the fact the tip-tilt mirror is also being used to generate the 30 Hz slow scan signal, a summing junction was used to send the filtered signals to the active mirror in the AOSLO.…”

“…The scanner itself was placed between the model eye lens and its retinal plane. In order to better understand the systems' latencies, the time it takes for the tip tilt mirror to move according to the TSLO motion trace was measured in real time with an oscilloscope; this was found to be 2.5 ms (also reported in [21]). In terms of digital tracking, any remaining high spatial resolution eye motion artifacts seen in the raw AOSLO video are corrected using the same strip and image based eye-tracking software as that described above for the TSLO system -i.e.…”

“…Yang et al described the use of a tip/tilt mirror for active closed-loop eye-tracking with an AOSLO over a 1.5° field of view (FOV) [20]. Additionally, eye-trackers have been added to OCT [21][22][23][24] and AO-OCT systems [25] in both the clinical and basic research domains, some utilizing the same TSLO technology we describe herein; particularly, the eye-tracker used by both Vienola et al and Braaf et al was a TSLO system designed and built in our lab [21,22]. Most recently, Kocaoglu et al used hardware based eye-tracking to limit image distortion and blur in AO-OCT images [25].…”