The healthy eye is perhaps the most fascinating part of the Human body; with the exception of the Brain. But in reality, the Retina, the back most part of the eye, is actually the most readily accessible part of the brain.

When the healthy human eye is focused on an object, the light reflected from the object is sent through the Cornea and Lens. The lens is "flexible" before the age of 40 years. After 40, it becomes more rigid and cannot refract light properly so that it focuses on the retina. At this time, glasses may be needed, especially for reading. This is called Accomodation. The incoming light rays are refracted and an up-side-down image is laid upon the back of the eye called the retina. Light is transmitted through the retina; which is composed of several layers of nerve cells; and strikes the back end of the retina. Here is where a layer of cells called the Photoreceptor Layer resides. It is composed of Rods (for night vision) and Cones (for finely detailed imaging in the light). The light is absorbed by the rods and cones and begins a process of information signaling that sends signals through a web of nerve cells that are in contact with the rods and cones. The information is directed indirectly, to the Retinal Ganglion Cells (RGC), which ultimately form the Optic Nerve. Light absorbed by the rods sends information to the Bipolar Cells and then to the Amacrine Cells and then to the RGC; whereas, light absorbed by the cones sends information to the bipolar cells and then directly to the RGC. The amacrine cells are axonless cells that modulate the visual information between the rods and cones and the RGC. There is also another type of nerve cell in the retina. It is called the Horizontal Cell, and it is responsible for lateral inhibition, which thereby increases contrast between the illuminated and the nonilluminated parts of the retina. They, sort of, allow the rods and cones to "talk" with each other.

On the retina, lies a highly concentrated section called the Macula, which has the highest visual acuity. At the center of the macula, lies a small indentation called the Fovea. The fovea is approximately 1.5 mm in diameter. It contains the highest density of cones and very few rods. The axons from the RGC in the fovea, lead to form the optic nerve at the Optic Disk. This is where the optic nerves lead into the visual system of the brain.

The RGC forms the optic nerve, which carries the signaling to the Visual System of the brain. The signals are processed by the Lateral Geniculate Nucleus (LGN), a sort of "processing" station in the brain. From the LGN the signals are sent on to the visual system where they are processed further and then sent to higher Cortical areas. Thus SIGHT is had.

The following sketches detail the structure of the eye and the cross section of the retina.