Eye tracking-based estimation and compensation of chromatic offsets for multi-wavelength retinal microstimulation with foveal cone precision.

Niklas Domdei,Michael Linden,Frank G Holz,Wolf M Harmening,Jenny L Reiniger

doi:10.1364/boe.10.004126

Abstract

Multi-wavelength ophthalmic imaging and stimulation of photoreceptor cells require consideration of chromatic dispersion of the eye, manifesting in longitudinal and transverse chromatic aberrations. Contemporary image-based techniques to measure and correct transverse chromatic aberration (TCA) and the resulting transverse chromatic offset (TCO) in an adaptive optics retinal imaging system are precise but lack compensation of small but significant shifts in eye position occurring during in vivo testing. Here, we present a method that requires only a single measurement of TCO during controlled movements of the eye to map retinal chromatic image shifts to the image space of a pupil camera. After such calibration, TCO can be compensated by continuously monitoring eye position during experimentation and by interpolating correction vectors from a linear fit to the calibration data. The average change rate of TCO per head shift and the correlation between Kappa and the individual foveal TCA are close to the expectations based on a chromatic eye model. Our solution enables continuous compensation of TCO with high spatial precision and avoids high light intensities required for re-measuring TCO after eye position changes, which is necessary for foveal cone-targeted psychophysical experimentation.

Highlights

Adaptive optics scanning laser ophthalmoscopy (AOSLO) coupled with microstimulation techniques enables imaging and simultaneous functional testing of targeted human photoreceptors in vivo
The specific techniques employed in these studies, using two beams of light of different wavelengths for imaging and stimulation, are faced with a particular challenge arising from the chromatic dispersion characteristics of the human eye
We here discuss our principle of Purkinje image based positional tracking, the relationship between transverse chromatic aberrations (TCA), transverse chromatic offset (TCO), and the angle Kappa of the eye, and its usability and application for single photoreceptor stimulation

Summary

Introduction

Adaptive optics scanning laser ophthalmoscopy (AOSLO) coupled with microstimulation techniques enables imaging and simultaneous functional testing of targeted human photoreceptors in vivo. This approach was recently employed to study single cone photoreceptor function [1,2], retinal circuitry [3,4], color vision [5,6], and sensitivity changes during retinal disease [7,8]. The specific techniques employed in these studies, using two (or more) beams of light of different wavelengths for imaging and stimulation, are faced with a particular challenge arising from the chromatic dispersion characteristics of the human eye. In an AOSLO system, this is currently achieved by a coaxial displacement of the light sources’ entry points

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