Retina, layer of nervous tissue that covers the inside of the back two-thirds of the eyeball, in which stimulation by light occurs, initiating the sensation of vision. The retina is actually an extension of the brain, formed embryonically from neural tissue and connected to the brain proper by the optic nerve. The retina is a complex transparent tissue consisting of several layers, only one of which contains light-sensitive photoreceptor cells. Light must pass through the overlying layers to reach the photoreceptor cells, which are of two types, rods and cones, that are differentiated structurally by their distinctive shapes and functionally by their sensitivity to different kinds of light. Rods predominate in nocturnal animals and are most sensitive to reduced light intensities; in humans they provide night vision and aid in visual orientation. Cones are more prominent in humans and those animals that are active during the day and provide detailed vision (as for reading) and colour perception. In general, the more cones per unit area of retina, the finer the detail that can be discriminated by that area. Rods are fairly well distributed over the entire retina, but cones tend to concentrate at two sites: the fovea centralis, a pit at the rear of the retina, which contains no rods and has the densest concentration of cones in the eye, and the surrounding macula lutea, a circular patch of yellow-pigmented tissue about 5 to 6 mm (0.2 to 0.24 inch) in diameter. Retinal diseases Retinal diseases vary widely, but most of them cause visual symptoms. Retinal diseases can affect any part of your retina, a thin layer of tissue on the inside back wall of your eye. The retina contains millions of light-sensitive cells (rods and cones) and other nerve cells that receive and organize visual information. Your retina sends this information to your brain through your optic nerve, enabling you to see. Treatment is available for some retinal diseases. Depending on your condition, treatment goals may be to stop or slow the disease and preserve, improve or restore your vision. Untreated, some retinal diseases can cause severe vision loss or blindness.
Symptoms: Many retinal diseases share some common signs and symptoms. These may include: Seeing floating specks or cobwebs Blurred or distorted (straight lines look wavy) vision Defects in the side vision Lost vision Risk factors Risk factors for retinal diseases might include aging, having diabetes or other diseases, eye trauma, and a family history of retinal diseases.
Journal Manager Journal of Eye Diseases and Disorderss