Using Adaptive Optics to Probe the Limits of Foveal Vision
Challenges in determining the limits to vision are imposed by the eye’s optical aberrations and eye movements. Both are large relative to the size of cones and receptive fields at and near the fovea. In an effort to overcome some of these challenges, we’ve developed systems in our lab that combine adaptive optics (AO) ophthalmoscopy with high speed eye tracking and targeted light delivery.
Adaptive optics is a set of techniques to measure and correct optical aberrations in real time. When used in an ophthalmoscope, AO faciliates images of living retina on the scale of single cells, such a cone photoreceptors.
To monitor eye motion, we integrate AO into a scanning laser imaging modality, where each image is uniquely distorted by the eye motion that has occurred during its acquisition (analogous to the distortions seen when you move a page while scanning with a photocopier or a flatbed scanner). Analyzing these distortions in real-time allows us to track the eye motion at frequencies over 1 kHz. More important, it allows us to place visible light stimuli to targeted locations on the retina - a single cone, for example.
I will describe how we’ve used this system for three basic vision science experiments.
1) We have used this system in tandem with electrophysiological recordings to determine connections between cones and their associated neurons upstream in the visual system. (Sincich et al, Nature Neuroscience, August, 2009)
2) We have used the AO system to bypass the optics and measure retinal an neural limits to acuity at and near the foveal center (Rossi and Roorda, Nature Neuroscience, February, 2010)
3) We have controlled the location of a visible stimulus on the retina with motion that is correlated, anti-correlated and uncorrelated with the eye’s natural motion to elucidate the conditions for which the ever-moving eye perceives the world as being stable (work in progress).