A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain. Retinal ganglion cells vary significantly in terms of their size, connections, and responses to visual stimulation but they all share the defining property of having a long axon that extends into the brain. These axons form the optic nerve, optic chiasm, and optic tract. A small percentage of retinal ganglion cells contribute little or nothing to vision, but are themselves photosensitive; their axons form the retinohypothalamic tract and contribute to circadian rhythms and pupillary light reflex, the resizing of the pupil. Function There are about 0.7 to 1.5 million retinal ganglion cells in the human retina. With about 4.6 million cone cells and 92 million rod cells, or 96.6 million photoreceptors per retina, on average each retinal ganglion cell receives inputs from about 100 rods and cones. However, these numbers vary greatly among individuals and as a function of retinal location. In the fovea (center of the retina), a single ganglion cell will communicate with as few as five photoreceptors. In the extreme periphery (edge of the retina), a single ganglion cell will receive information from many thousands of photoreceptors. Retinal ganglion cells spontaneously fire action potentials at a base rate while at rest. Excitation of retinal ganglion cells results in an increased firing rate while inhibition results in a depressed rate of firing. Types There is wide variability in ganglion cell types across species. In primates, including humans, there are generally three classes of RGCs: W-ganglion: small, 40% of total, broad fields in retina, excitation from rods. Detection of direction movement anywhere in the field. X-ganglion: medium diameter, 55% of total, small field, color vision. Sustained response. Y- ganglion: largest, 5%, very broad dendritic field, respond to rapid eye movement or rapid change in light intensity. Transient response. Based on their projections