Sagittal section of the adult human eye
The retina is a highly specialized neural tissue laying the eye. It contains two types of photoreceptors: the cones and the rods where they form the outer nuclear (ONL) and (OPL) plexiform layers of the retina. Cones detect the fine shape, the colors and movements of visual objects. They require high light intensity, and work in day light. The rods do not discriminate colors and are very sensitive to the low light intensities in night vision. The inner nuclear (INL) and plexiform (IPL) layers of the retina are composed of second-order neurons, i.e. cone bipolar cells, horizontal and amacrine cells.
The optic nerve (ON), located at the center of the retina, is composed of retinal ganglion axons running to the brain and, incoming blood vessels that open into the retina to vascularize the retinal layers and neurons. The retinal ganglion cells (RGC), i.e. the output neurons of the retina.
The macula lutea is a region of the central retina required for high acuity vision. The cones are predominant in the macula, whereas a majority of rods are located at the periphery. Although, the macula corresponds to less than 10% of the retinal surface, half of the retinal ganglion cells (RGCs) – i.e., neurons that form the optic nerve – are located in this region. The fovea centralis, located at the center of the macula lutea, is a depression in the inner retinal surface which is specialized of maximal visual acuity.