|Medical Dictionary - Dictionary of Medicine and Human Biology|
A half-carotene bearing the β (or β-ionone) form of the cyclic end group and a CH2OH at the C-15 position (numbering as in carotenoids) or 9′-position (numbering as a nonyl side chain on a cyclohexene ring); an intermediate in the vision cycle, it also plays a role in growth and differentiation. SEE ALSO: dehydroretinol. SYN: vitamin A1 alcohol, vitamin A1. r. dehydrogenase an oxidoreductase catalyzing interconversion of retinal and NADH to r. and NAD+.
Inflammation of the retina extending to the optic disk. r. of premature infants SYN: retinopathy of prematurity.
Noninflammatory degenerative disease of the retina. [retino- + G. pathos, suffering] arteriosclerotic r. r. distinguished by attenuated retinal arterioles with increased tortuosity, copper- or silver-wire appearance, perivascular sheathing, irregularity of lumen and scattered small hemorrhages, and small, sharp-edged deposits without surrounding edema. central angiospastic r. SYN: central serous choroidopathy. central serous r. SYN: central serous choroidopathy. circinate r. a retinal degeneration marked by a girdle of sharply defined white exudates around an edematous macula; usually bilateral and typically affects the aged. compression r. 1. See Berlin edema. See traumatic r.. diabetic r. retinal changes occurring in diabetes mellitus, marked by microaneurysms, exudates, and hemorrhages, and sometimes by neovascularization. SYN: fundus diabeticus.Diabetic eye disease is responsible for approximately 25% of all newly reported cases of blindness in the U.S. The principal form is nonproliferative r., which results directly from degenerative changes in retinal capillaries. Features of this disorder, as observed on funduscopic examination, include microaneurysms; soft or cotton-wool exudates, which are actually areas of microinfarction; hard or waxy exudates, which are deposits of lipid and protein from leaking capillaries; and flame hemorrhages. A few patients, principally those with type 1 diabetes, develop a proliferative r. characterized by neovascularization (proliferation of new capillary loops on the retinal surface). Either type of r. can impair vision by destroying retinal tissue directly and by predisposing to retinal edema, retinal detachment, and vitreous hemorrhage. Controlled clinical studies have shown that maintaining blood glucose levels as near as possible to normal at all times in persons with diabetes mellitus substantially retards the onset and rate of progression of r.. Laser photocoagulation is effective in arresting neovascularization in proliferative diabetic r.. dysproteinemic r. retinal venous congestion due to increased blood viscosity in dysproteinemia. electric r. SYN: photoretinopathy. external exudative r. exudative retinitis. hypertensive r. a retinal condition occurring in accelerated vascular hypertension, marked by arteriolar constriction, flame-shaped hemorrhages, cotton-wool patches, star-figure edema at the macula, and papilledema. Leber idiopathic stellate r. See neuroretinitis. leukemic r. appearance of the retina in all types of leukemia, characterized by engorgement and tortuosity of veins, scattered hemorrhages, and edema of the retina and disk. lipemic r. a milkiness of the retinal vessels (lipemia retinalis) combined with hard-edged fatty exudates, seen in patients with diabetic acidosis and hyperlipemia. macular r. SYN: maculopathy. pigmentary r. SYN: retinitis pigmentosa. r. of prematurity abnormal replacement of the sensory retina by fibrous tissue and blood vessels, occurring mainly in premature infants having a birth weight of less than 1500 g who are placed in a high-oxygen environment. SYN: retinopapillitis of premature infants, retrolental fibroplasia, Terry syndrome. proliferative r. neovascularization of the retina extending into the vitreous humor. SYN: retinitis proliferans. r. punctata albescens [MIM*136880] a disease in which both fundi show numerous white dots or flecks through the retinae, causing night blindness; autosomal dominant inheritance, caused by mutation in the “retinal degeneration, slow” gene (RDS) encoding peripherin on chromosome 6p. There is also a recessive form [MIM*210370]. Purtscher r. transient traumatic retinal angiopathy due to a sudden rise in venous pressure, as in compression of the body from seat belt injury; ocular fundi show large white patches associated with the retinal veins about the disk or macula, hemorrhages, and retinal edema; thought to be due to fat embolism from bone marrow. SYN: Purtscher disease, transient r., traumatic r.. renal r. hypertensive r. associated with chronic glomerulonephritis or nephrosclerosis. rubella r. peripheral pigmentary retinal changes in congenital rubella, not affecting visual function. sickle cell r. a condition marked by dilation and tortuosity of retinal veins and by microaneurysms and retinal hemorrhages; advanced stages may show neovascularization, vitreous hemorrhage, or retinal detachment. solar r. SYN: photoretinopathy. toxemic r. of pregnancy sudden angiospasm of retinal arterioles, later followed by retinal vascular signs of advanced hypertensive r.; vascular changes disappear rapidly after termination of the pregnancy. toxic r. retinal changes due to prolonged administration of various drugs. transient r. SYN: Purtscher r.. traumatic r. SYN: Purtscher r.. venous-stasis r. a uniocular r. associated with occlusion of the central retinal vein; a nonischemic central retinal vein occlusion. whiplash r. an injury to the retina caused by a sudden acceleration/deceleration injury.
A procedure to repair a detached retina by holding it in place; e.g., by producing chorioretinal adhesions by freezing (“retinal cryopexy”). [retino- + G. pexis, fixation] fluid r. a procedure to repair a detached retina by holding it in place with a fluid that is heavier than vitreous fluid. gas r. a retinal detachment repair in which the retina is held in place by an expandable gas. SYN: pneumatic r.. pneumatic r. SYN: gas r..
Repositioning a detached retina by pressing it into position by gas or fluid. See retinopexy. [retino- + G. piesis, pressure]
Degenerative splitting of the retina, with cyst formation between the two layers. [retino- + G. schisis, division] juvenile r. [MIM*268100] r. occurring before 10 years of age and within the nerve-fiber layer, with frequent macular involvement; at first, the inner wall is a translucent veil-like membrane, but it becomes more dense and may render the retina white; autosomal recessive inheritance. There is a form of this condition in middle age that is X-linked [MIM*312700] and a rare autosomal dominant form [MIM*180270]. senile r. r. occurring most often in the elderly and affecting the outer plexiform layer; it begins in the extreme inferotemporal periphery and is not significantly progressive; vision usually is good.
An optical device used to illuminate a subject's retina during retinoscopy. [retino- + G. skopeo, to view] luminous r. a portable optical device providing either a circular or linear (streak) beam of light. reflecting r. a plane or concave mirror with a central perforation that allows the observer to see rays emerge from the subject's eye.
A method of determining errors of refraction by illuminating the retina and observing the rays of light emerging from the eye. SYN: scotoscopy, shadow test, skiascopy. [retino- + G. skopeo, to view] cylinder r. determination of spherical, astigmatic, and refractive error using cylindric lenses. fogging r. the method of reducing vision with convex lenses until accommodation is suspended; a static, noncycloplegic technique.
A surgical incision through the retina.
retinyl phosphate (ret′i-nil fos′fat)
The phosphoester of all-trans-retinol; essential for the biosynthesis of certain glycoproteins needed for growth regulation and for mucous secretion.
The reticular cells related to the reticular fiber network, as in the stroma of lymphatic tissue. [L. rete, net, + G. peri, around, + Mod. L. thelium, fr. G. thele, nipple]
1. A flasklike vessel with a long neck passing outward, once used in distilling. 2. A small furnace. [Mediev. L. retorta, fem. pp. of retorqueo, pp. -tortus, to twist or bend back]
A genus of protozoan flagellates, one species of which, R. intestinalis, is found occasionally in the human intestine, although it is nonpathogenic and infrequently reported. [L. re-torqueo, to twist back, + G. monas, single, a unit]
To shrink, draw back, or pull apart. [L. re-traho, pp. -tractus, a drawing back]
Retractable; capable of being drawn back.
1. A shrinking, drawing back, or pulling apart. 2. Posterior movement of teeth, usually with the aid of an orthodontic appliance. [L. retractio, a drawing back] gingival r. 1. lateral movement of the gingival margin away from the tooth surface; may be indicative of underlying inflammation or pocket formation; 2. displacement of the marginal gingivae away from the tooth by mechanical, chemical, or surgical means. mandibular r. a type of facial anomaly in which the gnathion lies posterior to the orbital plane.
retractor (re-trak′ter, -tor)
1. An instrument for drawing aside the edges of a wound or for holding back structures adjacent to the operative field. 2. A muscle that draws a part backward, e.g., the middle part of the trapezius muscle is a r. of the scapula; the horizontal fibers of the temporalis muscle serve to retract the mandible. Desmarres r. an instrument used to withdraw an eyelid.
Backward; toward the back part; directed posteriorly. [L. retro, backward, + ad, to]
retrahens aurem, retrahens auriculam (ret′ra-henz aw′rem, aw-rik′u-lam)
See auricularis posterior (muscle). [L. drawing back the ear, or auricle]
retreat from reality
Substitution of imaginary satisfactions or fantasy for relations with the real world.
The cutting away of superfluous tissue. [F. re-, back, + trancher, to cut]
The third stage in the memory process, after encoding and storage, involving mental processes associated with bringing stored information back into consciousness. SEE ALSO: memory.
Backward or behind. [L. back, backward]
Behind the auricle.
Relating to the back part of, or behind, the cheek.
Behind the eyeball. SYN: retro-ocular.
SYN: achillobursitis. [retro- + L. calcaneum heel, + bursitis]
Posterior to the cecum.
Posterior to the cervix uteri.
1. A going back; a relapse. 2. Cessation of the external symptoms of a disease followed by signs of involvement of some internal organ or part. 3. Denoting a position of the uterus or other organ farther back than is normal. [L. retro-cedo, pp. -cessus, to go back, retire]
A form of acupressure for the arrest of bleeding; the needle is passed through the tissues above the cut end of the artery, is turned around, and then is passed backward beneath the vessel to come out near the point of entrance. [retro- + L. claudo (cludo) to close]
Posterior to the colon. [retro- + G. kolon, colon]
Relating to the back of the neck; drawing back the head. [retro- + L. collum, neck]
SYN: retrograde VA conduction.
Running backward. [retro- + L. cursus, a running]
A backward bending or inclining.
Any backward displacement, such as retroversion or retroflexion of the uterus.
Posterior to the esophagus.
Placement of a sealing material into the apical foramen of a dental root from the apical end.
Bent backward or posteriorly. SYN: retroflected. [retro- + L. flecto, pp. flexus, to bend]
Backward bending, as of the uterus when the corpus is bent back, forming an angle with the cervix. SYN: retroflection. r. of iris abnormal position of the iris on the ciliary body after severe concussion.
Denoting a state in which the mandible is located posterior to its normal position in relation to the maxillae.
A condition of facial disharmony in which one or both jaws are posterior to normal in their craniofacial relationships; usually used in reference to the mandible. [retro- + G. gnathos, jaw]
1. Moving backward. 2. Degenerating; reversing the normal order of growth and development. [L. retrogradus, fr. retro- + gradior, to go]
SYN: mirror-writing. [retro- + G. grapho, to write]
SYN: cataplasia. [L. retrogressus fr. retrogradior, to go backwards]
SYN: feedback inhibition.
Posterior to the iris.
The washing out of a cavity by the backward flow of an injected fluid. [L. retro, backward, + jacio, to throw]
retrojector (re′tro-jek-ter, -tor)
A form of syringe with long tubular attachment to the nozzle, used in retrojection.
Posterior to the lens of the eye. SYN: retrolenticular (1) .
1. SYN: retrolental. 2. Behind the lentiform nucleus of the brain.
Relating to the back part of the tongue; posterior to the tongue. [retro- + L. lingua, tongue]
Posterior to the mamma.
Posterior to the lower jaw. [retro- + L. mandibula, lower jaw]
Posterior to the mastoid process; relating to the posterior mastoid cells.
Distal (or posterior) to the last erupted (or present) molar tooth.
retromorphosis (re-tro-mor′fo-sis, -mor-fo′sis)
SYN: cataplasia. [retro- + G. morphosis, process of forming]
Posterior nasal; relating to the posterior nares.
External or posterior to the peritoneum.
SYN: retroperitoneal space. [retro- + peritoneum]
Inflammation of the cellular tissue behind the peritoneum. idiopathic fibrous r. SYN: retroperitoneal fibrosis.
Posterior to the pharynx.
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