How the Retina Works*

Excerpt

Much of the interpretation of our visual world takes place in the retina itself through the actions of specialized neural circuits. Rods and cones, whose distributions and interactions with other retinal neurons have evolved differently among species, form the initiating elements of these circuits. Neurons within the retina, horizontal cells, amacrine cells, bipolar cells, and ganglion cells, extract salient elements from the rod and cone sensory layer using patterns of selective excitatory and inhibitory, often novel, synaptic connections within the retinal synaptic layers. The retina segregates these extracted image elements into parallel output pathways specifying image features and transmits them for further analysis to brain visual centers. The system is adaptive to conditions of illumination, sometimes employing locally diffusing neuromodulators to signal global changes in scene. All this image processing occurs within a photosensitive sheet of neural tissue less than half a millimeter thick. This review previews and highlights the content of Webvision, a tutorial website containing a set of chapters written by experts in the field on the elements of visual-system anatomy and function, focusing on retina, its embryonic development, image processing capabilities, disruptions in disease, prospects for cure, and implications for nervous system research.