Photoreceptor cell cell depends upon only the number of photons absorbed. The different responses of the three types of cone cells are determined by the likelihoods that their respective photoreceptor proteins will absorb photons of different wavelengths. So, for example, an L cone cell contains a photoreceptor protein that more readily absorbs long wavelengths of light (i.e., more "red"). Light of a shorter wavelength can also produce the same response, but it must be much brighter to do so. The human retina contains about 120 million rod cells, and 6 million cone cells. The number and ratio of rods to cones varies
Retina stage. Recently Ader and colleagues in Dublin showed, using the electron microscope, that transplanted photoreceptors formed synaptic connections. In 2012, Sebastian Seung and his laboratory at MIT have launched EyeWire, an online Citizen science game where players trace neurons in the retina. The goals of the EyeWire project are to identify specific cell types within the known broad classes of retinal cells, and to map the connections between neurons in the retina, which will help to determine how vision works. Retina The retina is the innermost, light-sensitive layer, or "coat", of shell tissue of the eye of most vertebrates and