[Organization of the retina: structure/function relations and a species comparison of retinal ganglion cells]

The retina contains a range of ganglion cell types that differ in morphology and in their response to visual stimuli. They extract different image parameters and transmit them to the brain in independent parallel channels. One type, the alpha cells, shows a phasic response to light stimuli and covers a relatively large retinal area of about 1 degree to 3 degrees diameter. They are important for the detection of movement and global form, but not for high visual acuity. In a comparative study, alpha cells were found in all mammalian species investigated. They comprise only 1%-4% of all ganglion cells. However, with their large dendritic fields and regular soma spacing they provide complete coverage of the retina and contribute to image analysis at each retinal location. As alpha cells are a consistent component of mammalian retinae, they are most likely also a functional constituent of the human retina. The functional properties of different ganglion cell types have a bearing on the clinical diagnosis, because retinal damage (e.g., in glaucoma patients) may be specific to the cell type.