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Christy K. Sheehy, David W. Arathorn, Qiang Yang, Pavan Tiruveedhula, Austin Roorda; High-speed, Image-based Eye Tracking With A Scanning Laser Ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3086.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate a confocal scanning laser ophthalmoscope (SLO) system for accurate, real-time, high-frequency, image-based eye tracking and targeted stimulus delivery.
Ever-present eye motion, even during fixation, generates unique distortions in scanned retinal images. A system for measuring and compensating these distortions in real-time was demonstrated previously for an adaptive optics SLO (Yang et al Optics Express 18(17):17841-17858 (2010)). We also showed that the by-product of correcting the image distortions was a high frequency eye trace. Here, we explore whether the same image-based techniques can be applied to conventional, non-AO, SLOs. A confocal SLO optical design was done using ZEMAX (Radiant ZEMAX LLC, Bellevue, Washington) for optical optimization and Solidworks (Concord, MA) for the optomechanical components. The system employs mirror-based telescopes to avoid back reflections, a resonant/galvanometer scanner combination for adjustable field sizes, and an adjustable pupil size for controlling light collection, image quality, and depth of focus. The instrument optics (not including the eye) were optimized to provide diffraction-limited performance over an 8 degree field of view. Scan frequencies were set to provide 512 x 512 pixel images at a rate of ~30 Hz. The eye tracking was done by measuring the intraframe image distortions in real time using a custom-designed FPGA frame grabber.
High quality retinal videos were readily obtained in the system. A stabilized view of the retina was rendered in real time and eye motion signals were generated at frequencies as high as 450 Hz.
A well-designed confocal SLO can be used to provide real-time eye motion estimates at 450 Hz and possibly higher. Two primary applications for this system are (i) to offer image-guided and targeted placement of a retinal stimulus for psychophysics and vision testing systems, and (ii) to provide robust, high resolution, high frequency eye tracking signals for guiding other high resolution imaging systems such as OCT and AOSLO.
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