Linking Structure And Function In The Human Visual System With Adaptive Optics
Seminar | March 13 | 12-1:30 p.m. | 489 Minor Hall
Will S. Tuten, OD, PhD
In humans, fine-scale spatio-chromatic vision is the result of neural processes initiated in cone photoreceptors. The overarching goal of my research is to understand how the cellular architecture of the cone mosaic shapes vision, both in healthy subjects and in patients with retinal disease. Adaptive optics scanning laser ophthalmoscopy (AOSLO) enables high-resolution imaging of retinal structures and the precise delivery of diffraction-limited psychophysical stimuli to targeted locations, thereby facilitating examination of structure-function relationships at the cellular level.
In the first part of my talk, I will describe experiments in which a multi-wavelength AOSLO was used to obtain single-cone sensitivities from parafoveal photoreceptors whose spectral types had been identified by absorptance imaging. By modulating the relative activity of the long (L) and middle (M) wavelength cones with chromatic adapting fields, we found perceptual evidence for spatial antagonism between adjacent cones. The spatial and spectral patterns of these interactions were consistent with lateral inhibition mediated by retinal horizontal cells that assimilate input from L and M cones indiscriminately. This finding implies the cone-specific circuitry supporting red-green color vision emerges after the first retinal synapse, and, more broadly, suggests a platform for psychophysically elucidating features of early visual circuitry.
The second half of my talk will focus on ongoing work aimed at translating cone-targeted psychophysics to the clinical realm. Previous studies suggest that conventional perimetric techniques may be relatively insensitive to incipient visual dysfunction in the central retina, in part because the coarse stimuli they employ are mismatched to the fine neural grain of the macula. By contrast, a cone-by-cone assessment of visual function in patients is impractical. With this in mind, we used an areal summation paradigm to examine the spatial scales over which cone signals pool linearly in the central retina. An AOSLO recently equipped with microperimetry capabilities was used to compensate for ocular aberrations and fixational eye movements, facilitating a more direct measure of neural summation in the visual system. Despite minimizing the influence of these pre-neural factors, we found evidence that cone signals pool linearly across multiple receptors in the fovea. These results will be discussed in the context of previous work, and similar measurements obtained recently from patients with choroideremia, an inherited outer retinal degeneration, will be presented.