optomeninx

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]

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]

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, Vitiligo

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.

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.

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]