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retina
ret·i·na R0193200 (rĕt′n-ə)n. pl. ret·i·nas or ret·i·nae (rĕt′n-ē′) A delicate, multilayered, light-sensitive membrane lining the inner eyeball and connected by the optic nerve to the brain.
[Middle English, from Medieval Latin rētina, from Latin rēte, net.]
ret′i·nal adj.retina (ˈrɛtɪnə) n, pl -nas or -nae (-ˌniː) (Anatomy) the light-sensitive membrane forming the inner lining of the posterior wall of the eyeball, composed largely of a specialized terminal expansion of the optic nerve. Images focused here by the lens of the eye are transmitted to the brain as nerve impulses[C14: from Medieval Latin, perhaps from Latin rēte net] ˈretinal adjret•i•na (ˈrɛt n ə, ˈrɛt nə)
n., pl. ret•i•nas, ret•i•nae (ˈrɛt nˌi) the innermost coat of the posterior part of the eyeball that receives the image produced by the lens, is continuous with the optic nerve, and consists of several layers, one of which contains the rods and cones that are sensitive to light. [1350–1400; Middle English ret(h)ina < Medieval Latin rētina, perhaps = Latin rēt-, s. of rēte net + -ina -ine3] Ret•in-A (ˌrɛt nˈeɪ)
Trademark. a brand of tretinoin, used esp. to reduce wrinkles caused by overexposure to the sun. ret·i·na (rĕt′n-ə) The light-sensitive membrane that lines the inside of the back of the eyeball, connected to the brain by the optic nerve. The retina of vertebrate animals contains specialized cells, called rods and cones, that absorb light.retina - From Latin rete, "net," as there is a net of nerves making up this layer of the eyeball.See also related terms for net.retina
The back of the eyeball where neurons convert light into electrical impulses that pass through the brain. See cones, rodsThesaurus| Noun | 1. |  retina - the innermost light-sensitive membrane covering the back wall of the eyeball; it is continuous with the optic nerveneuroepithelium - epithelium associated with special sense organs and containing sensory nerve endingseye, oculus, optic - the organ of sighttissue layer, membrane - a pliable sheet of tissue that covers or lines or connects the organs or cells of animals or plantsfovea, fovea centralis - area consisting of a small depression in the retina containing cones and where vision is most acuteparafovea - area of the retina immediately surrounding the foveamacula lutea, macular area, yellow spot, macula - a small yellowish central area of the retina that is rich in cones and that mediates clear detailed visionvisual cell - one of the cells of the retina that is sensitive to lightoptic disc, optic disk, blind spot - the point where the optic nerve enters the retina; not sensitive to lightcone cell, retinal cone, cone - a visual receptor cell in the retina that is sensitive to bright light and to colorretinal rod, rod cell, rod - a visual receptor cell that is sensitive to dim light |
Translationsretina (ˈretinə) noun the part of the back of the eye that receives the image of what is seen. 視網膜 视网膜
retina
retina: see visionvision,
physiological sense of sight by which the form, color, size, movements, and distance of objects are perceived. Vision in Humans
The human eye functions somewhat like a camera; that is, it receives and focuses light upon a photosensitive receiver, the retina.
..... Click the link for more information. ; eyeeye,
organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of eye are the simple eye, found in many invertebrates, and the compound eye, found in insects and many other
..... Click the link for more information. .Retina the internal membrane of the eye, which converts light stimulation into nervous excitation and effects the primary processing of visual signals. The retina lines the fundus of the eye and covers the ciliary body and the internal surface of the iris; thus, three distinct parts of the retina are distinguished—the pars optica retinae (consisting of ten layers), the pars ciliaris retinae, and the pars iridica retinae. In vertebrates, including man, the retina is formed during embryonic development from the optic vesicles (primary eye rudiments), which are paired lateral evaginations of the rudimentary forebrain. By means of invagination of the distal wall, each optic vessel is converted into an optic cup. The external layer of the optic cup, which is formed by the optic-vesicle wall closest to the brain, develops into pigmented epithelium, whose cells contain granules of the pigment melanin. The external layer of the optic cup is adjacent to the internal surface of the vascular tunic. Cytoplasmic processes (outgrowths) extend from the cells of the vascular tunic toward photoreceptor cells. The remaining retinal layers develop from the inner wall of the optic cup. The outer nuclear layer consists of the nuclear parts of the photoreceptors, whose processes extend beyond the external limiting membrane toward the cell processes of the pigmented epithelium; the external limiting membrane is a thickened layer of the endings of the cell processes of Müller’s fibers. In the outer molecular layer, centrad photoreceptor processes form synapses with the dendrites of the cells of the inner nuclear layer. The latter layer contains the nuclear parts of amacrine neurons (which lack axons) and bipolar and horizontal neurons. It also contains glial elements (Müller’s fibers), which perform supportive and trophic functions in the retina. The inner molecular layer is formed by the centrad processes of bipolar neurons, which come into contact with the neuronal dendrites of the ganglion cell layer. The ganglion cell layer consists of multipolar ganglion cells, whose axons form layers of nerve fibers; the optic nerve consists of ganglion cells. The ganglion cell layer also contains efferent fibers that extend from the brain’s visual area to the retina. The internal limiting membrane, which is the innermost retinal layer, is formed (as is the external limiting membrane) by the cell processes of Müller’s fibers. A distinct oval elevation called the optic disk is found on the posterior surface of the optic part of the retina. The point of exit of the optic nerve from the retina forms the blind spot. In the central part of the fundus of the eye and not far from the blind spot is the macula lutea, within which there is a central depression that contains the maximum number of cone cells per unit of retinal surface. This is the area of keenest vision on the retina. Photoreceptor cells transmit signals to cells of the inner nuclear layer, which in turn direct visual signals to the ganglion cells. Information reaches the brain’s visual area along the centrad processes of ganglion cells. Signals are conducted along the retina in various ways. For example, in the macula lutea, signals are conducted from cone cells to bipolar cells in a predominantly isolated manner; each bipolar cell communicates with a ganglion cell, which ensures the greatest keenness of vision in this area. Toward the retinal periphery, the concentration of cones decreases and the number of rods increases; here, several rod and cone cells are in contact with a bipolar cell and several bipolar cells are in contact with a ganglion cell. When compared with the isolated conduction of information, this type of aggregation results in stronger visual signals being sent by ganglion cells to the brain and in increased photosensitivity. The human retina contains approximately 7 million cone cells and 75–150 million rod cells. In many vertebrate animals, including fish, amphibians, and birds, fluctuations in the illumination of the photoreceptors is regulated by the retinomotor reaction, which coordinates the movements of pigmented granules in the cell processes of pigmented epithelium and the expansion or contraction of the processes of rods and cones perpendicularly to the retinal surface. At twilight or in complete darkness, pigment granules gather in the nuclear parts of pigmented-epithelium cells, whereas the cell processes, which are deprived of pigment granules, remain transparent. The external segment of the rods moves nearer the external limiting membrane, and the external segment of the cones moves between the cell processes of the pigmented epithelium. When illumination increases most pigment granules migrate into the cell processes of the pigmented epithelium, and the external segments of the rods move outward and arrange themselves between the processes. At the same time, the cones move closer to the external limiting membrane, where previously, under weak illumination, the external processes of the rods had been located. The movements of the external processes of rods and cones during the retinomotor reaction are caused by the contractility of the myoid. As a result of the retinomotor reaction, rods, which are more photosensitive than cones, screen themselves with pigment granules from excessive excitation by light. REFERENCESFiziologiia sensornykh sistem, part 1: Fiziologiia zreniia. Leningrad, 1971. (Rukovodstvo po fiziologii.)
Keidel, W. D. Fiziologiia organov chuvstv, part 1. Moscow, 1975. (Translated from German.)O. G. STROEVA retina[′ret·ən·ə] (computer science) In optical character recognition, a scanning device. (neuroscience) The photoreceptive layer and terminal expansion of the optic nerve in the dorsal aspect of the vertebrate eye. retina the light-sensitive membrane forming the inner lining of the posterior wall of the eyeball, composed largely of a specialized terminal expansion of the optic nerve. Images focused here by the lens of the eye are transmitted to the brain as nerve impulses Retina
retina [ret´ĭ-nah] the innermost of the three tunics of the eye" >eye, surrounding the vitreous body and continuous posteriorly with the optic nerve. The retina is composed of light-sensitive neurons arranged in three layers; the first layer is made up of rods and cones and the other two transmit impulses from the rods and cones to the optic nerve. The rods are sensitive in dim light, and the cones are sensitive in bright light and are responsible for color vision.Disorders of the Retina. retinopathies are pathologic conditions of the retina; they occur in conjunction with certain systemic disorders, such as hypertension, nephritis, toxemia of pregnancy, and diabetes mellitus.detachment of the retina is complete or partial separation of the retina from the choroid, the middle coat of the eyeball. It occurs most often in persons with myopia (nearsightedness), but it also can result from trauma to the head. Structure of the retina showing the rods and cones. From Applegate, 2000.ret·i·na (ret'i-nă), [TA] Grossly, the retina consists of three parts: optic, ciliary, and iridial. The optic part, the physiologic portion that receives the visual light rays, is further divided into two parts, the pigmented part (pigment epithelium) and the nervous part, which are arranged in the following ten layers: pigmented layer; layer of inner and outer segments (of rods and cones); outer limiting layer (actually a row of junctional complexes); outer nuclear layer; outer plexiform layer; inner nuclear layer; inner plexiform layer; ganglionic (cell) layer; layer of nerve fibers; and inner limiting layer. Layers 2-10 comprise the neural layer. At the posterior pole of the visual axis is the macula, in the center of which is the fovea, the area of acute vision. Here, layers 6-9 and blood vessels are absent, and only elongated cones are present. About 3 mm medial to the fovea is the optic disc, where axons of the ganglionic cells converge to form the optic nerve. The ciliary and iridial parts of the retina are forward prolongations of the pigmented layer and a layer of supporting columnar or epithelial cells over the ciliary body and the posterior surface of the iris, respectively. Synonym(s): optomeninx [Mediev. L. prob. fr. L. rete, a net] retina (rĕt′n-ə)n. pl. retinas or retinae (rĕt′n-ē′) A delicate, multilayered, light-sensitive membrane lining the inner eyeball and connected by the optic nerve to the brain.
ret′i·nal adj.ret·i·na (ret'i-nă) [TA] The light-sensitive membrane forming the innermost layer of the eyeball. Grossly, the retina consists of three parts: optic part of retina, ciliary part of retina, and iridial part of retina. The optic part, the physiologic portion that receives the visual light rays, is further divided into two parts, pigmented part (pigment epithelium) and nervous part, which are arranged in the following layers: 1) pigment epithelium; 2) layer of rods and cones; 3) external limiting lamina, actually a row of junctional complexes; 4) external nuclear lamina; 5) external plexiform lamina; 6) internal nuclear lamina; 7) internal plexiform lamina; 8) ganglionic cell lamina; 9) lamina of nerve fibers; 10) internal limiting lamina. Layers 2-10 comprise the nervous part. At the posterior pole of the visual axis is the macula, in the center of which is the fovea, the area of acute vision. Here layers 6-9 and blood vessels are absent, and only elongated cones are present. About 3 mm medial to the fovea is the optic disc, where axons of the ganglionic cells converge to form the optic nerve. The ciliary and iridial parts of the retina are forward prolongations of the pigmented layer and a layer of supporting columnar or epithelial cells over the ciliary body and the posterior surface of the iris, respectively. [Mediev. L. prob. fr. L. rete, a net]retina (rĕt′ĭ-nă) plural.retinae [L.]  RETINA OF THE RIGHT EYE RETINA: Microscopic structure of optic disk areaThe innermost layer of the eye, which receives images transmitted through the lens and contains the receptors for vision, the rods and cones. See: illustrationretinal (-năl), adjectiveThe retina is a light-sensitive membrane on which light rays are focused. It extends from the entrance point of the optic nerve anteriorly to the margin of the pupil, completely lining the interior of the eye. It consists of three parts. The pars optica, the nervous or sensory portion, extends from the optic disk forward to the ora serrata, a wavy line immediately behind the ciliary process; the pars ciliaris lines the inner surface of the ciliary process; and the pars iridica forms the posterior surface of the iris. Slightly lateral to the posterior pole of the eye is a small, oval, yellowish spot, the macula lutea, in the center of which is a depression, the fovea centralis. This region contains only cones and is the region of the most acute vision. About 3.5 mm nasally from the fovea is the optic papilla (optic disk), where nerve fibers from the retina make their exit and form the optic nerve. This region is devoid of rods and cones and is insensitive to light; hence it is named the blind spot. The layers of the retina, in the order light strikes them, are the optic nerve fiber layer, ganglion cell layer, inner synaptic layer, bipolar cell layer, outer synaptic layer, layer of rods and cones, and pigment epithelium. See: illustration ColorThe retina is normally red, reflecting blood flow, and is pale in anemia or ischemia. VesselsThe arteries are branches of a single central artery, which is a branch of the ophthalmic artery. The central artery enters at the center of the optic papilla and supplies the inner layers of the retina. The outer layers, including rods and cones, are nourished by capillaries of the choroid layer. The veins lack muscular coats. They parallel the arteries; blood leaves by a central vein that leads to the superior ophthalmic vein. coarctate retinaA condition in which there is an effusion of fluid between the retina and choroid, giving the retina a funnel shape. shot-silk retinaA retina having an opalescent appearance, sometimes seen in young persons.tigroid retinaA retina having a spotted or striped appearance, seen in retinitis pigmentosa.retina The complex membranous network of nerve cells, fibres and photoreceptors that lines the inside of the back of the eye and converts optical images formed by the lens system of the eye into nerve impulses. The retina contains colour-blind but very sensitive rods and colour-sensitive cones and a computing system that refines the signals produced by these. The impulses leave each retina by way of about one million nerve fibres that form the optic nerve. Fig. 269 Retina. retina the lining of the interior of the vertebrate eye containing a concentration of photoreceptor cells known as rods and cones that are connected to the optic nerve via BIPOLAR CELLS. The retina lies immediately in front of the vascular choroid layer which nourishes it.RetinaLight sensitive layer of the eye, that consists of four major layers: the outer neural layer, containing nerve cells and blood vessels, the photoreceptor layer, a single layer that contains the light sensing rods and cones, the pigmented retinal epithelium (PRE) and the choroid, consisting of connective tissue and capillaries.Mentioned in: Cataract Surgery, Cataracts, Color Blindness, Eye and Orbit Ultrasounds, Eye Examination, Eye Glasses and Contact Lenses, Eye Muscle Surgery, Glaucoma, Hyperopia, Macular Degeneration, Microphthalmia and Anophthalmia, Myopia, Photorefractive Keratectomy and Laser-Assisted In-Situ Keratomileusis, Radial Keratotomy, Retinal Artery Occlusion, Retinal Vein Occlusion, Retinoblastoma, Uveitis, Vitiligoretina The light-receptive, innermost nervous tunic of the eye. It is a thin transparent membrane (about 125 μm near the ora serrata, 350 μm near the macula and 560 μm near the optic disc). The retina proper has an area of about 266 mm2. It lies between the vitreous body and the choroid, and extends from the optic disc to the ora serrata. Near the posterior pole and temporal to the optic disc is the macula, at the centre of which is the foveola which provides the best visual acuity. The retina contains at least 10 distinct layers, of which there are two synaptic layers. They are from the outermost layer to the innermost: (1) the pigment epithelium; (2) the layer of rods and cones; (3) the external limiting membrane; (4) the outer nuclear layer; (5) the outer molecular (outer plexiform) layer; (6) the inner nuclear layer (which contains the bipolar, amacrine and horizontal cells and nuclei of the fibres of Mueller); (7) the inner molecular (inner plexiform) layer; (8) the ganglion cell layer; (9) the nerve fibre (layer stratum opticum); and (10) the internal limiting membrane. The two synaptic layers where visual signals must synapse as they emerge from the rods and cones on their way to the optic nerve are the two molecular layers (5 and 7) (Fig. R9). The blood supply to the retina is composed of the capillaries from the central retinal artery, which supply the inner two-thirds of the retina up to the outer plexiform layer, and the choriocapillaris, which supplies the outer one-third. There is no retinal circulation in the foveola (avascular zone). A blood-retina barrier is created by the walls of the retinal capillaries which restrict the movement of molecules, which could be damaging to neural tissue or interfere with function, from the inside to the outside of the capillaries. The blood-retina barrier in the outer third of the retina is formed by the tight junctions of the retinal pigment epithelium cells. See astrocytes; optic cup; optic disc; ectoderm; ocular fundus; fibre layer of Henle; macula; neurotransmitter; neurosensory retina; retinitis; retinopathy; rhodopsin; transduction.
converse retina See inverted retina.
fleck retina Term referring to a retina with multiple, small or yellow spots, which are seen in various conditions: actinic keratopathy, drusen, fundus albipunctatus, fundus flavimaculatus.
inverted retina Term referring to the fact that the retina of vertebrates is orientated so that the light has to pass through all the neuronal layers before reaching the photo-receptors. However, the retina of invertebrates is normally orientated so that light passes first through the photoreceptors as it traverses the retina: such a retina is called a verted or converse retina.
lattice degeneration of the retina A vitreoretinal degeneration usually found between the equator and the ora serrata leading to a thinning of the retina and characterized by a lesion made up of fine white lines and some pigmentation. It may result in holes or tears and in rhegmatogenous retinal detachment by which time the patient usually complains of floaters. The condition is most common in myopes and often found in patients with Marfan's syndrome. See retinal break; retinal detachment; retinoschisis; Marfan's syndrome.
leopard retina See leopard fundus.
neurosensory retina This is composed of all the layers of the retina, except the outer pigmented layer (called retinal pigment epithelium). It comprises three main groups of neurons: (1) the photoreceptors, (2) the bipolar cells, and (3) the ganglion cells. In addition, there are other connecting neurons: the horizontal and amacrine cells. The neurosensory layer is derived embryologically from the inner layer of the optic cup whereas the pigmented layer is derived from the outer layer of the optic cup and they are separated by a potential space which facilitates their separation, as occurs in detached retina. Syn. sensory retina.
tessellated retina See tessellated fundus.
tigroid retina See tessellated fundus.
verted retina See inverted retina. " > Fig. R9 Schematic representation of the cells and layers of the central primate retina (1: retinal pigment epithelium; 2: layer of rods and cones; 3: external limiting membrane; 4: outer nuclear layer; 5: outer plexiform layer; 6: inner nuclear layer; 7: inner plexiform layer; 8: ganglion cell layer; 9: nerve fibre layer; 10: internal limiting membrane)
| Table R2 Some approximate retinal dimensions | | | diameter | | | | structure | | mm | | degrees | | distance from centre of foveola | | foveola | | 0.4 | | 1.3 | | | | fovea centralis | | 1.5 | | 5.0 | | | | macula lutea | | 4.0 | | 14 | | | | optic disc* | | | | | | | | horizontal | | 1.8 | | 6.0 | | | | vertical | | 2.1 | | 7.5 | | | | nasal disc margin | | | | | | 5.5 mm or 18.5 | | temporal disc margin | | | | | | 3.5 mm or 12.5 | | centre of disc | | | | | | 4.6 mm or 15.5 | | *The figures given for the size of the disc are those corresponding to the blind spot. Anatomically the optic disc is slightly smaller. |
ret·i·na (ret'i-nă) [TA] Grossly, section of eye that consists of three parts: optic, ciliary, and iridial. The optic part, the physiologic portion that receives the visual light rays, is further divided into two parts, the pigmented part (pigment epithelium) and the nervous part. [Mediev. L. prob. fr. L. rete, a net]FinancialSeeVisionRETINA
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retina
Related to retina: Retina DisplayWords related to retinanoun the innermost light-sensitive membrane covering the back wall of the eyeballRelated Words- neuroepithelium
- eye
- oculus
- optic
- tissue layer
- membrane
- fovea
- fovea centralis
- parafovea
- macula lutea
- macular area
- yellow spot
- macula
- visual cell
- optic disc
- optic disk
- blind spot
- cone cell
- retinal cone
- cone
- retinal rod
- rod cell
- rod
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