retina /ret·i·na/ (ret´ĭ-nah) [L.] the innermost tunic of the eyeball, containing the neural elements for reception and transmission of visual stimuli.
Retina
retina
retina (ret´
n),
ret·i·na (r t n- )n. pl. ret·i·nas or ret·i·nae (r tn-  ) The delicate multilayered light-sensitive membrane lining the inner posterior chamber of the eyeball containing the rods and cones and connected by the optic nerve to the brain. ret i·nal adj. |
Retina
Light 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.
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retina
[ret′inə]
Etymology: L, rete, net
a 10-layered, delicate nervous tissue membrane of the eye, continuous with the optic nerve, that receives images of external objects and transmits visual impulses through the optic nerve to the brain. The retina is soft and semitransparent and contains rhodopsin. It consists of the outer pigmented layer and the nine-layered retina proper. These nine layers, starting with the most internal, are the internal limiting membrane, the stratum opticum, the ganglion cell layer, the inner plexiform layer, the inner nuclear layer, the outer plexiform layer, the outer nuclear layer, the external limiting membrane, and the layer of rods and cones. The outer surface of the retina is in contact with the choroid, the inner surface with the vitreous body. The retina is thinner anteriorly, where it extends nearly as far as the ciliary body, and thicker posteriorly, except for a thin spot in the exact center of the posterior surface where focus is best. The photoreceptors end anteriorly in the jagged ora serrata at the ciliary body, but the membrane of the retina extends over the back of the ciliary processes and the iris. The retina becomes clouded and opaque if exposed to direct sunlight. See also Jacob x membrane, macula, optic disc.
retina (ret´
n),n a 10-layered, delicate nervous-tissue membrane of the eye, continuous with the optic nerve, that receives images of external objects and transmits visual impulses through the optic nerve to the brain.
retina
the innermost of the three tunics of the eyeball, surrounding the vitreous body and continuous posteriorly with the optic nerve. The retina is composed of two parts: an optical part in the fundus of the eye that is sensitive to light, and a nonsensitive pigmented part that lines the ciliary body and iris. The light-sensitive neurons are 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 to dim light of a variety of wavelengths, and the cones are sensitive to bright light of more restricted wavelengths and are responsible for color vision. Visual acuity is greatest in the central part of the retina. See also eye.
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Retina of the dog. By permission from Aspinall V, O'Reilly M, Introduction to Veterinary Anatomy and Physiology, Butterworth Heinemann, 2004
silent retina syndrome
see sudden acquired retinal degeneration.
retina
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.
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.
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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. | ||||||
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