“R” selections in the Glossary of Terms for
Anatomy, Physiology & Pathology of the Human Eye

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radial keratotomy (RK)
surgical procedure to correct myopia by flattening the curvature of the cornea via a series of 4 to 16 equally spaced radial cuts in the peripheral cornea; may leave extensive scars on the cornea, causing glare in bright light and possibly interfering with the wearing of contact lenses (in case the myopia is not fully corrected)

radiation, infrared (IR)
electromagnetic radiation with a wavelength outside the visible spectrum at its violet end; used of radiation having a wavelength between about 700 nanometers and 1 millimeter

radiation, optic
see optic radiation

radiation, ultraviolet (UV)
electromagnetic radiation with a wavelength outside the visible spectrum at its red end; used of radiation having a wavelength shorter than that of visible light and longer than that of x-rays

real image
the image formed by a convex lens (or a concave mirror), on the opposite side of the lens from which the light is entering; the image is formed at the focal point of the lens, at a distance (focal length) away from the lens, in meters, equal to the inverse of the dioptric power of the lens

rebound hyperemia
continual engorgement of blood vessels (such as those in the conjunctiva) due to chronic use of a vasoconstricting drug, due to a weakening of the smooth muscles constricting the vessels, creating a need for more of the vasoconstrictor to be used to have the same vasoconstricting effect

rectus muscle
any of four muscles of the eyeball that arise from the border of the optic foramen and run forward to insert into the sclera of the eyeball; medial rectus inserts into the medial (nasal) aspect of the sclera; lateral rectus inserts into the lateral (temporal) aspect of the sclera; superior rectus inserts into the superior aspect of the sclera; inferior rectus inserts into the inferior aspect of the sclera

refractive error
an eye condition such as hyperopia, myopia, astigmatism, or presbyopia that prevents a clear image from being focused on the retina without excessive focusing or the use of corrective lenses

Reiter’s syndrome
a disease that usually is initiated by infection in genetically predisposed individuals and typically is characterized by recurrence of arthritis, conjunctivitis, and urethritis

layer of nervous tissue, covering the back two-thirds of the eyeball, in which stimulation by light initiates an electrochemical reaction in which electrical impulses are transmitted to the brain, producing the sensation of vision; actually an extension of the brain, formed embryonically from brain tissue and connected to the brain proper by the optic nerve

retinal arteries
arteries in the retina; salmon to red in color; about 1 1/3 to 2 times the diameter of retinal veins; see central retinal artery

retinal blood vessels
see retinal arteries and retinal veins

retinal detachment (RD)
see detachment, retinal (RD)

retinal hemorrhage
bleeding into the retina; caused by such things as infections, trauma, hypertensive retinopathy, diabetic retinopathy, central vein occlusion, hematologic abnormalities, central nervous system vascular malformations, prolonged and vigorous cardiopulmonary resuscitation, or high-altitude mountain climbing

retinal tear
a rip in the retina; caused by such things as trauma or a pulling on a weak section of retina by the attached vitreous; can result in a vitreous hemorrhage if the retina tears across a blood vessel

retinal veins
veins in the retina; salmon to orange in color; about 1/2 to 3/4 the diameter of retinal arteries; see central retinal vein

retinitis pigmentosa (RP)
degeneration of the retina manifested by night blindness and gradual loss of peripheral vision, eventually resulting in tunnel vision or total blindness

any diseased condition of the retina, especially one that is noninflammatory

retrobulbar optic neuritis
inflammation of the optic nerve, usually unilateral, affecting the part of the nerve behind the eyeball, sometimes accompanied by mild optic disc hyperemia but an otherwise normal retina, and almost always accompanied by central vision loss and pain on moving the eye; occurs due to multiple sclerosis and other disorders which cause papillitis, but most often due to idiopathic (unknown) causes

rheumatoid arthritis
see arthritis

a bright red photosensitive pigment found in the retinal rod photoreceptors that is similar to iodopsin (in cone photoreceptors) but is less labile; contains opsin (a protein) and retinene (a light absorbing compound which is derived from Vitamin A); important in scotopic vision

the elongated, rod-shaped light-sensitive receptor cells of the retina that function in dim-light and night vision and in the perception of size, shape, and brightness of visual images; composed of an outer segment (containing the photoreceptor molecule rhodopsin), inner segment, cell body, and synaptic region; about 120 to 130 million per eye, much more than the number of cones; densest accumulation is in the retinal periphery, with none being present in the fovea; absent in the optic disc (optic nerve head)

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