Real-time compensation for dynamic changes in transverse chromatic aberration with pupil decentration in a tracking scanning laser ophthalmoscope

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In the last decade, image-based eye tracking has been used in conjunction with scanning laser ophthalmoscopy (SLO) to achieve stabilized stimulus delivery. This has proven useful for microperimetry testing of patients with visual impairment and in psychophysical experiments aiming to elucidate the relationship between physiology and behavior by way of microstimulation of single cone photoreceptors. For functional testing with SLO, near-IR light is typically used for imaging and eye tracking and shorter wavelengths are used for stimulation, requiring careful correction for chromatic aberration. While longitudinal chromatic aberration is approximately constant across observers, transverse chromatic aberration (TCA) varies substantially. Positional offsets between wavelengths can be corrected by updating the timing of stimulus delivery in the raster scan, however, TCA changes dynamically within an experimental session when the pupil becomes decentered. With multi-wavelength imaging in an adaptive optics SLO, Privitera et al. (2016) showed that TCA offset changed linearly with pupil position by an average of 3.5 arcminutes per millimeter of pupil displacement. We sought to compensate for changes in TCA offset by simultaneously tracking pupil position and updating stimulus delivery. First, we recorded pupil positions while subjects performed a Vernier-like alignment task in a tracking SLO. From this, we determined each subject's TCA offset as a function of pupil displacement, with results similar to Privitera et al. Next, we implemented real-time compensation using each subject's TCA per mm pupil shift ratio. TCA offsets with pupil shift were corrected and much of the variability in performance was removed. Privitera, C., Sabesan, R., Winter, S., Tiruveedhula, P., & Roorda, A. (2016). Eyetracking technology for real-time monitoring of transverse chromatic aberration. Optics Letters, 41(8), 1728–1731.

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