There are about 0.7 to 1.5 million<unk> s in the human<unk>  With about 4.6 million cone<unk> s and 92 million rod<unk> s, or 96.6 million photoreceptors per<unk>  on average each<unk>  receives inputs from about 100 rods and cones. However, these numbers vary greatly among individuals and as a function of<unk>  location. In the fovea (center of the<unk> , a single<unk> <unk>  will communicate with as few as five photoreceptors. In the extreme periphery (edge of the<unk> , a single<unk> <unk>  will receive information from many thousands of photoreceptors.<unk> s spontaneously fire action potentials at a base rate while at rest. Excitation of<unk> s results in an increased firing rate while inhibition results in a depressed rate of firing. A false-color image of a flat-mounted rat<unk> viewed through a fluorescence microscope at 50x magnification. The optic nerve was injected with a fluorophore, causing<unk> s to fluoresce.
Retinal ganglion cell
Sustentacular cell
Pseudounipolar neuron
Granule cell
Magnocellular neurosecretory cell
Corneal endothelium
Iris pigment epithelium
Corneal keratocyte