Visual Streak

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The Visual Streak is the area of highest acuity in the retina of many species. In humans and some other mammals, the location of highest acuity in the retina is a circular area termed the fovea or area centralis. In contrast, some animals (such as rabbits) have a visual streak. In such animals, the area of greatest acuity in their retina is not a single point, but rather an elongated "streak" running across the retina. This allows for better detection of movement in the periphery. In all species studied, the area of highest acuity (whether fovea or visual streak) boasts the highest concentration of cones, the lowest concentration of rods, and much smaller receptive field sizes for all cells. Bipolar cells in this region are smaller, as are ganglion cells. One example of a cell type whose shape is highly correlated to their location with respect to the visual streak is starburst amacrine cells (SACs). SACs also display structural changes as the perpendicular distance from the visual streak increases. Nearest the visual streak, both type a and b SACs have a relatively small cell body size and dendritic field diameter as well as a relatively high frequency of branching and frequency of synaptic boutons. As we move perpendicularly away from the visual streak, cell body size and dendritic field diameter increases, while the frequency of branching and synaptic boutons decreases.