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- Radial Keratotomy (RK)
- Surgical procedure where patterned surgical incisions are made in the peripheral area of
the cornea. As these incisions heal, the cornea is flattened to the degree required to make
the desired refractive error correction. This early refractive vision correction procedure
has been largely replaced by newer, more accurate procedures such as LASIK.
See Refractive Surgery in
Eye Care Encyclopedia.
- red eye
- Any condition that causes the white part of the eye to look red. Redness usually is because
of engorged blood vessels on the surface of the eye or hemorrhaging on the surface. In
making a diagnosis, an eye doctor will pay close attention to the location and pattern of
redness.
See Free Eye Tests.
- reflectance
- The fraction of light that is reflected toward the eye by an object.
- refraction: objective
- Eye test utilizing an automated device called an Auto Refractor that instantly measures the
power of the eye and the outer shape of the eye. The device needs no input from the
patient such as that required by the “Which is better? 1 or 2” question used in a phoropter exam.
See Free Eye Tests.
- refraction: subjective
- Eye test using a phoropter where patient is given choices between lens 1 and 2, providing
the examining eye doctor with “subjective” information regarding which prescription will
make the patient more comfortable.
- refractive error
- Optical defect of the eye that causes light rays to focus in front of the retina (nearsighted),
behind the retina (farsighted), or in several different places on the retina (astigmatic),
resulting in less than perfect vision. These defects can normally be corrected with
eyeglasses, contact lenses or refractive eye surgery.
See Free Eye Tests.
- refractive surgery
- Elective eye surgery which corrects optical defects of the eye by either changing the shape
of the cornea or by inserting a plastic lens to supplement the eye’s natural focusing ability.
See Refractive Surgery in
Eye Care Encyclopedia.
See Free Eye Tests.
- refractor
- Instrument that aids an eyecare professional in determining the proper corrective
prescription for a patient with less-than-perfect vision.
- replacement schedule
- Schedule for the length of time a specific type of contact lens should be worn. Extended
wear lenses can be worn without interruption, even while sleeping, up to a maximum number
of days as specified by the eye doctor, while other types of lenses may require removal
every evening before bedtime. It’s important to differentiate between wear schedules for
various lenses.
- retina
- Thin membrane that covers the inside of the back two-thirds of the eye. Retina converts
images into electrical impulses to be sent along the optic nerve to the brain and be
converted into images that allow vision.
See Retina in Eye Care Encyclopedia.
See Free Eye Tests.
- retina evaluation
- retinal detachment
- Painless disorder where patient may notice gradual raising or lowering of a curtain over
the visual field of the affected eye. May occur with aging of eye or as a result of trauma.
Caused by a detachment of the retina from the back of the eye, often from the “pulling”
effect of the vitreous, the jelly-like ball that fills most of the eye behind the lens. Patient
may also notice a sudden increase in “floaters” or flashing lights. Any such symptoms
require an immediate visit to an ophthalmologist.
See Free Eye Tests.
- retinal hole
- With age, the retina starts to thin and weaken especially near its attachments with the front
of the eye (periphery). In addition, the jelly-like ball that fills most of the eye behind the
lens, called the vitreous, changes from a firm substance to a loose fluid. When the vitreous
becomes fluid, it can easily move and tug on its attachments and become detached, pulling
a small bit of retina with it. When this happens, a hole is left in the retina.
See Free Eye Tests.
- retinal
- A form of vitamin A called retinal is responsible for transmitting light sensation in the retina of the eye. Deficiency of vitamin A leads to night blindness.
- retinal rivalry
- The perception of first one then the other of two visual stimuli, which differ in color or form when they are presented at the same time to congruent areas of both eyes
- retinitis pigmentosa
- Any of several hereditary progressive degenerative diseases of the eye marked by night blindness in the early stages, atrophy and pigment changes in the retina, constriction of the visual field, and eventual blindness. Also called pigmentary retinopathy
See Free Eye Tests.
- retinoblastoma
- Hereditary, malignant intraocular tumor that develops from retinal cells. If untreated,
numerous seedling nodules produce secondary tumors, gradually filling the eye and
extending along the optic nerve and to the brain, ending in death. Most common childhood
ocular malignancy.
See Free Eye Tests.
- RGP
- Acronym for Rigid Gas Permeable. Durable contact lenses made of polymers that transmit
oxygen and allow longer wearing times than other rigid lenses. Because RGPs do not
contain water, they resist deposits and are not prone to harboring bacteria. These lenses
are often larger in diameter to increase comfort.
See Free Eye Tests.
- rhabdomyosarcoma
- A malignant tumor composed of striated muscle fibers
- rhodopsin
- The visual pigment in rod cells. Also called visual purple.
- river blindness
- Onchocerciasis, a disease caused by a parasitic worm (Onchocerca volvulus) transmitted by biting blackflies (buffalo gnats) that breed in fast-flowing rivers. The adult worms can live for up to 15 years in nodules beneath the skin and in the muscles of infected persons, where they produce millions of worm embryos (microfilariae) that invade the skin and other tissues including the eyes. About 18 million persons are affected, mostly in Africa and also in Yemen and Latin America. Both living and dead microfilariae cause severe itching in the skin and sometimes blindness after many years.
Since 1987, the drug ivermectin (brand name: Stromectol) has been provided by the manufacturer (Merck) free of charge. A single oral dose administered once a year prevents the accumulation of microfilariae in persons at risk. No drug suitable for mass treatment can kill the adult worms in the body, and therefore, onchocerciasis cannot be wiped out. The blindness, however, can be eliminated.
- RK
- Acronym for Radial Keratomy. Surgical procedure where patterned surgical incisions are
made in the peripheral area of the cornea in order to reshape the cornea to the degree
required for the desired refractive error correction.
See Refractive Surgery in Eye Care Encyclopedia.
See Free Eye Tests.
- rod
- A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provides side vision and the ability to see objects in dim light (night vision).
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