Of course we know now that there are multiple visual pathways and each one of these visual pathways mediates a different aspect or derivative of a component of vision. It turns out that vision is complex, more complex than simply carrying “visual pixels” to the brain to be mapped out topologically. After photon capture by the photoreceptors of the eye and pre-processing operations in the circuitry of the retina, information is passed to the retinal ganglion cells or the output cells of the retina. Each one of the 18-20 types of ganglion cells that project out of the retina through the optic nerve mediates different kinds of information. Aside from projections to the primary visual cortex, some ganglion cells project to the lateral geniculate nucleus, others to the superior colliculus, the pretectum, the suprachiasmatic nucleus and the hypothalamus. Each one of these projections out of the retina carries information relevant to a different feature of vision. Some of these functions help control the size of your pupil limiting the amount of light that comes into the eye. Other projections help you orient your head and eyes to the world around you while other projections still help you figure out what time of day and season it is. Most of these meta-visual functions are not conscious, but play crucial roles in how we live our everyday lives and are only revealed when things in the visual system go awry like the man Oliver Sacks described who could catch a ball despite being completely and functionally blind. Milena Channing’s experience with a stroke in her visual cortex reveals some of this unconscious aspect of seeing, ironically by causing blindness while preserving portions of the brain involved in motion detection.
This image of ganglion cells, Müller cells and starburst amacrine cells in the human retina is from a patient suffering from retinitis pigmentosa (RP). This disease this patient suffered from slowly causes people affected with this disease to go blind and is a constant reminder to me of why we engage in our research.
For some, this is a pretty, though abstract image created through a set of technologies called computational molecular phenotyping (CMP). The colors in this image come from antibodies labeling taurine, glutamine and glutamate, all small molecular species that reveal metabolic states in these tissues.
For us, these images reveal variation in cell types as well as abnormalities in other kinds of cells that presage retinal stress and the cellular responses that alter the retina in ways that both cause blindness and make it difficult to rescue vision loss. We also see the beginnings of changes in the circuitry of the retina that forever will alter the way that diseased retinas process information.
Image courtesy of Bryan William Jones, Ph.D. and originally appeared here.
I ran across this interesting vignette from Astronaut Cmdr. Hadfield (his Twitter account here) on how sight changes in space including the flattening of eyeballs, swelling around the optic nerve and the random flashes of light seen by astronauts.
This paper is the result of a collaborative effort between Bryan William Jones, Mineo Kondo and Hiroko Terasaki, Carl Watt, Kevin Rapp, James Anderson, Yanhua Lin, Maggie Shaw, Jia-Hui Yang and Robert Marc.