TThe light-sensitive membrane that lines the back inner surface of the eye, and on which images are cast by the cornea and lens. The retina contains specialized nerve cells (rods and cones) that convert light energy into nerve impulses. The impulses travel from the rods and cones through other cells in the retina and along the optic nerve to the brain. The rods respond to very dim light and cones are responsible for colour vision.
The retina can be affected by congenital and genetic disorders, such as colour vision deficiency and Tay–Sachs disease. It can also be infected, injured (see retinal detachment; retinal tear), or affected by tumours such as retinoblastoma. Other disorders affecting the retina include diabetes mellitus and retinal vein occlusion.
n. the light-sensitive layer that lines the interior of the eye. The outer part of the retina (retinal pigment epithelium; RPE), next to the *choroid, is pigmented to prevent the passage of light. The inner part, next to the cavity of the eyeball, contains *rods and *cones (light-sensitive cells) and their associated nerve fibres (see illustration). A large number of cones is concentrated in a depression in the retina at the back of the eyeball called the *fovea. —retinal adj.
Blockage of an artery supplying blood to the retina, most commonly due to thrombosis or embolism, The disorder can result in permanent blindness or loss of part of the field of vision, depending on the artery affected and whether or not the condition can be treated quickly enough.... retinal artery occlusion
(ARN) severe inflammation and necrosis of the retina associated with inflammation and blockage of retinal blood vessels, haemorrhage and death of retinal tissue, and retinal detachment. It may affect both eyes (bilateral acute retinal necrosis, BARN), and visual prognosis is poor. ARN is thought to be due to viral infection.... acute retinal necrosis
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