Overview of retinal disorders

[Tariq Zaki]

The retina is the transparent, light-sensitive structure at the back of the eye. The cornea and lens focus light onto the retina. The central area of the retina, called the macula, contains a high density of color-sensitive photoreceptor (light-sensing) cells. These cells, called cones, produce the sharpest visual images and are responsible for central and color vision. The peripheral area of the retina, which surrounds the macula, contains photoreceptor cells called rods, which respond to lower light levels but are not color sensitive. The rods are responsible for peripheral vision and night vision.
The optic nerve carries signals generated by the photoreceptors (cones and rods). Each photoreceptor is joined to the optic nerve by a tiny nerve branch. The optic nerve is connected to nerve cells that carry signals to the vision center of the brain, where they are interpreted as visual images.
The optic nerve and the retina have a rich supply of blood vessels that carry blood and oxygen. Part of this supply of blood vessels comes from the choroid, which is the layer of blood vessels that lies between the retina and the outer white layer of the eye called the sclera. The central retinal artery (the other major source of blood to the retina) reaches the retina near the optic nerve and then branches out within the retina. Blood drains from the retina into branches of the central retinal vein. The central retinal vein exits the eye within the optic nerve.
When examining a person