Projects

Probing spatial and chromatic vision with small-spot psychophysics

During daytime, most humans are capable of perceiving fine spatial detail and a rich palette of colors. This sensory capacity is remarkable considering our visual percepts are constructed from just three types of photoreceptor signals—those arising from L, M, and S cones. Individual cone signals are scalar, varying only in magnitude. As a result, the spatial and spectral characteristics of the light driving a single cone are not encoded in its output. To obtain an accurate estimate of the spatio-chromatic structure of the world, the circuitry of the retina and brain must process the signals originating in cones across space and time. We use single-cone psychophysics to study these processes near the human fovea, where our visual sense is finest.

Figure modified from Tuten et al. (2017), showing single-cone threshold maps (left panel) obtained when M-cone activity was elevated by a blue adapting field. The arrangement of the L, M, and S cones is shown on the right. The pattern of sensitivity could be explained by lateral inhibition mediated by horizontal cells.

Structure-function relationships in retinal disease

Degenerative diseases of the outer retina result in the death of rod and cone photoreceptors. These structural losses necessarily occur at the cellular scale, and have traditionally been studied by histology—either in animal models or in post-mortem human tissue. By contrast, much of our knowledge about the functional consequences of degenerative retinal disease has been acquired using relatively coarse tools for probing vision: visual acuity measurements and conventional automated perimetry. To examine structure-function relationships at the cellular scale in living eyes, we use multi-modal adaptive optics high-resolution retinal imaging in conjunction with precise cone-targeted stimulation. The tools we develop to achieve this have the potential to enhance our understanding of how retinal diseases develop, progress, and respond to therapeutic intervention. Diseases studied with adaptive optics microperimetry include age-related macular degeneration, macular telangiectasia (MacTel), and choroideremia.

This high-resolution retinal image was obtained using AOSLO near the fovea (white star) of a patient with MacTel Type II. The bright, tightly-packed spots arise from light reflected back from outer segments of individual cone photoreceptors; the dim and honeycomb-like regions are areas of presumed cone disruption. Colored markers represent the visual sensitivity of the underlying structure (green/red = high/low sensitivity); marker squares are scaled to the retinal size of the test stimulus. Locations 5 and 6 show reduced but measurable sensitivity in a region of apparent cone loss. For more details, see Wang et al. (2015).