AND VISION TERMS
from the Dictionary of Eye Terminology
terms -- symptoms, tests, treatments, surgery, diseases & conditions,
anatomy -- eye doctors use. These definitions can help you understand
from Dictionary of Eye Terminology,
copyright 1990-2007 by Barbara Cassin and Triad Communications. The
Dictionary's more than 5,000 entry terms define anatomy, tests,
diseases and conditions, refractive errors, surgical procedures, drugs
and medications, etc. Learn more about the Dictionary of Eye
information given is for information purposes only and is not intended
to replace professional medical advice from your physician, or to
diagnose or treat a health problem or disease.
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V / W / Y / Z
(uh-kah-muh-DAY-shun). Increase in optical power by the eye in order
to maintain a clear image (focus) as objects are moved closer. Occurs
through a process of ciliary muscle contraction and zonular
relaxation that causes the elastic-like lens
to "round up" and increase its optical power. Natural
loss of accommodation with increasing age is called presbyopia.
secondary cataract. Remnants of an opaque lens remaining in
the eye, or opacities forming, after extracapsular cataract removal.
macular degeneration (AMD, ARMD) (MAK-yu-lur). Group of conditions
that include deterioration of the macula,
resulting in loss of sharp central vision. Two general types: "dry,"
which is more common, and "wet," in which abnormal new
blood vessels grow under the retina and leak fluid and blood (neovascularization),
further disturbing macular function. Most common cause of decreased
vision after age 60.
(am-blee-OH-pee-uh), "lazy eye." Decreased
vision in one or both eyes without detectable anatomic damage to
the retina or visual pathways. Usually uncorrectable by eyeglasses
or contact lenses.
grid (AM-slur). Test card. Printed grid (black lines
on white background or white lines on black background) used for
detecting central visual field distortions or defects, such as in
macular degeneration. x
anterior chamber angle. Junction of the front surface of the
iris and back surface of the cornea,
where aqueous fluid filters out of the eye.
chamber. Fluid-filled space inside the eye between the iris
and the innermost corneal surface (endothelium).
(AY-kwee-us), aqueous humor. Clear, watery fluid that fills
the space between the back surface of the cornea and the front surface
of the vitreous, bathing the lens. Produced by the ciliary processes.
Nourishes the cornea, iris, and lens and maintains intraocular pressure.
Type of ultrasound; very high frequency sound waves that are reflected
by the ocular structures and converted into electrical impulses.
Used for measuring length of eyeball (axial length) prior to cataract
surgery, to help determine power of IOL to be implanted; also to
help differentiate normal and abnormal eye tissue.
(uh-STIG-muh-tiz-um). Refractive error. Optical defect in
which refractive power is not uniform in all directions (meridians).
Light rays entering the eye are bent unequally by different meridians,
which prevents formation of a sharp image focus on the retina. Slight
uncorrected astigmatism may not cause symptoms, but a large amount
may result in significant blurring and headache.
retinopathy. See diabetic
bifocals. Eyeglasses that incorporate two different powers in
each lens, usually for near and distance corrections.
vision. Blending of the separate images seen by each eye into
one composite image.
(blef-uh-RI-tus). Inflammation of the eyelids, usually with redness,
swelling, and itching.
spot. Sightless area within the visual field of a normal eye.
Caused by absence of light sensitive photoreceptors where the optic
nerve enters the eye.
Type of ultrasound; provides a cross-section view of tissues that
cannot be seen directly. High frequency sound waves are reflected
by eye tissues and orbital structures and converted into electrical
pulses, which are displayed on a printout.
Opacity or cloudiness of the crystalline lens,
which may prevent a clear image from forming on the retina. Surgical
removal of the lens may be necessary if visual loss becomes significant,
with lost optical power replaced with an intraocular lens, contact
lens, or aphakic spectacles. May be congenital or caused by trauma,
disease, or age.
cataract extraction. Removal of a cloudy lens from the eye.
An extracapsular cataract extraction leaves the rear lens
capsule intact; with an intracapsular extraction there is
complete removal of lens with its capsule, usually by cryoextraction.
retinal artery. First branch of the ophthalmic artery; supplies
nutrition to the inner two-thirds of the retina.
retinal vein. Blood vessel that collects retinal venous blood
drainage; exits the eye through the optic nerve.
vision. An eye's best vision; used for reading and discriminating
fine detail and color. Results from stimulation of the fovea and
the macular area.
(kuh-LAY-zee-un). Inflamed lump in a meibomian gland (in the eyelid).
Inflammation usually subsides, but may need surgical removal. Sometimes
called an internal hordeolum.
(KOR-oyd). Vascular (major blood vessel) layer of the eye lying
between the retina and the sclera. Provides nourishment to outer
layers of the retina.
blindness. Reduced ability to discriminate between colors, especially
shades of red and green. Usually hereditary.
Light-sensitive retinal receptor cell that provides sharp visual
acuity and color discrimination.
(kahn-junk-TI-vuh). Transparent mucous membrane covering the outer
surface of the eyeball except the cornea, and lining the inner surfaces
of the eyelids.
(kun-junk-tih-VI-tis), "pink eye. " Inflammation
of the conjunctiva. Characterized by discharge, grittiness, redness
and swelling. Usually viral in origin, but may be bacterial or allergic;
may be contagious.
Inward movement of both eyes toward each other, usually in an effort
to maintain single binocular vision as an object approaches.
(KOR-nee-uh). Transparent front part of the eye that covers the
iris, pupil, and anterior chamber and provides most of an eye's
lens. See lens.
refraction. Assessment of an eye's refractive error after lens
accommodation has been paralyzed with cycloplegic eyedrops (to eliminate
variability in optical power caused by a contracting lens). Series
of lenses in graded powers are presented to determine which provide
the sharpest, clearest vision.
retinopathy (ret-in-AHP-uh-thee). Spectrum of retinal changes
accompanying long-standing diabetes mellitus. Early stage is background
retinopathy. May advance to proliferative retinopathy,
which includes the growth of abnormal new blood vessels (neovascularization)
and fibrous tissue.
dilated pupil. Enlarged pupil, resulting from contraction of
the dilator muscle or relaxation of the iris sphincter. Occurs normally
in dim illumination, or may be produced by certain drugs (mydriatics,
cycloplegics) or result from blunt trauma.
(D) (di-AHP-tur). Unit to designate the refractive power of
double vision. Perception of two images from one object; images
may be horizontal, vertical or diagonal.
(DRU-zin). Tiny, white hyaline deposits on Bruch's membrane (of
the retinal pigment epithelium). Common after age 60; sometimes
an early sign of macular degeneration.
eye syndrome. Corneal and conjunctival dryness due to deficient
tear production, predominantly in menopausal and post-menopausal
women. Can cause foreign body sensation, burning eyes, filamentary
keratitis, and erosion of conjunctival and corneal epithelium.
(ek-TROH-pee-un). Outward turning of the upper or lower eyelid so
that the lid margin does not rest against the eyeball, but falls
or is pulled away. Can create corneal exposure with excessive drying,
tearing, and irritation. Usually from aging.
emmetropia (em-uh-TROH-pee-uh). Refractive state of having no
refractive error when accommodation is at rest. Images of distant
objects are focused sharply on the retina without the need for either
accommodation or corrective lenses.
(en-TROH-pee-un). Inward turning of upper or lower eyelid so that
the lid margin rests against and rubs the eyeball.
(ee-soh-TROH-pee-uh), cross-eyes. Eye misalignment in which
one eye deviates inward (toward nose) while the other fixates normally.
laser (EKS-ih-mur). Class of ultraviolet lasers that removes
tissue accurately without heating it. In refractive corneal surgery,
controlled by computer to make precise pre-programmed shavings of
eye tissue to produce a given optical correction.
(eks-oh-TROH-pee-uh), wall-eyes. Eye misalignment in which
one eye deviates outward (away from nose) while the other fixates
muscles (eks-truh-AHK-yu-lur). Six muscles that move the eyeball
(lateral rectus, medial rectus, superior oblique, inferior oblique,
superior rectus, inferior rectus).
Structures covering the front of the eye, which protect it, limit
the amount of light entering the pupil, and distribute tear film
over the exposed corneal surface.
floaters. Particles that float in the vitreous and cast shadows
on the retina; seen as spots, cobwebs, spiders, etc. Occurs normally
with aging or with vitreous detachment, retinal tears, or inflammation.
angiography (FLOR-uh-seen an-jee-AH-gruh-fee).Technique used
for visualizing and recording location and size of blood vessels
and any eye problems affecting them; fluorescein dye is injected
into an arm vein, then rapid, sequential photographs are taken of
the eye as the dye circulates.
(FOH-vee-uh). Central pit in the macula that produces sharpest vision.
Contains a high concentration of cones and no retinal blood vessels.
(glaw-KOH-muh). Group of diseases usually characterized by increased intraocular
pressure resulting in damage to the optic nerve and retinal nerve
fibers. A common cause of preventable vision loss. May be treated
by prescription drugs or surgery.
gonioscopy (goh-nee-AHS-koh-pee). Examination of the anterior
chamber angle through a goniolens (special type of contact lens).
(hi-pur-OH-pee-uh), farsightedness. Refractive error.
Focusing defect in which an eye is underpowered; light rays coming
from a distant object strike the retina before coming to sharp focus,
blurring vision. Farsighted people expend focusing effort to see
clearly in the distance, and close-up vision is blurred because
it takes even more focusing effort. Corrected with additional optical
power, which may be supplied by a plus lens (spectacle or contact)
or by excessive use of the eye's own focusing ability (accommodation).
hyphema (hi-FEE-muh). Blood in the anterior chamber, such as
following blunt trauma to the eyeball.
(intraocular lens). Plastic lens that may be surgically implanted
to replace the eye's natural lens.
intraocular pressure. 1. Fluid pressure inside the eye. 2. The
assessment of pressure inside the eye with a tonometer. Also called
Pigmented tissue lying behind the cornea that gives color to the
eye (e.g., blue eyes) and controls amount of light entering the
eye by varying the size of the pupillary opening.
(kehr-uh-toh-KOH-nus). Degenerative corneal disease affecting vision.
Characterized by generalized thinning and cone-shaped protrusion
of the central cornea, usually in both eyes. Hereditary.
gland. Almond-shaped structure that produces tears. Located
at the upper outer region of the orbit, above the eyeball.
Acronym: Light Amplification by Stimulated Emission of Radiation.
High energy light source that uses light emitted by the natural
vibrations of atoms (of a gas or solid material) to cut, burn or
dissolve tissues for various clinical purposes: in the retina, to
treat diabetic retinopathy and macular degeneration, to destroy
leaking and new blood vessels (neovascularization); on the iris
or trabecular meshwork, to decrease pressure in glaucoma; after
extracapsular cataract extraction, to open the posterior lens capsule.
(LAY-sik). Acronym: LAser in SItu Keratomileusis. Type of refractive
surgery in which the cornea is reshaped to change its optical power.
A disc of cornea is raised as a flap, then an excimer laser is used
to reshape the intrastromal bed, producing surgical flattening of
the cornea. Used for correcting myopia, hyperopia, and astigmatism.
eye. " See amblyopia.
blindness. Best-corrected visual acuity of 20/200 or less, or
reduction in visual field to 20¡ or less, in the better seeing eye.
crystalline lens. The eye's natural lens. Transparent, biconvex
intraocular tissue that helps bring rays of light to a focus on
vision. Term usually used to indicate vision of less than 20/200.
Small central area of the retina surrounding the fovea; area of
acute central vision.
(mi-OH-pee-uh), nearsightedness. Focusing defect in which
the eye is overpowered. Light rays coming from a distant object
are brought to focus before reaching the retina. Requires a minus
lens correction to "weaken" the eye optically and permit
clear distance vision.
(nee-oh-VAS-kyu-lur-ih-ZAY-shun). Abnormal formation of new blood
vessels, usually in or under the retina or on the iris surface.
May develop in diabetic retinopathy, blockage of the central retinal
vein, or macular degeneration.
(ni-STAG-mus). Involuntary, rhythmic side-to-side or up and down
(oscillating) eye movements that are faster in one direction than
(ahf-thal-MAH-loh-jist). Physician (MD) specializing in diagnosis
and treatment of refractive, medical and surgical problems related
to eye diseases and disorders.
disc, optic nerve head. Ocular end of the optic nerve. Denotes
the exit of retinal nerve fibers from the eye and entrance of blood
vessels to the eye.
(ahp-TISH-un). Professional who makes and adjusts optical aids,
e.g., eyeglass lenses, from refraction prescriptions supplied by
an opthalmologist or optometrist.
nerve. Largest sensory nerve of the eye; carries impulses for
sight from the retina to the brain.
(ahp-TAHM-uh-trist). Doctor of optometry (OD) specializing in vision
problems, treating vision conditions with spectacles, contact lenses,
low vision aids and vision therapy, and prescribing medications
for certain eye diseases.
Discipline dealing with the diagnosis and treatment of defective
eye coordination, binocular vision, and functional amblyopia by
non-medical and non-surgical methods, e.g., glasses, prisms, exercises.
Covering an amblyopic patient's preferred eye, to improve vision
in the other eye.
(puh-RIM-ih-tree). Test. Method of charting extent of a stationary
eye's field of vision with test objects of various sizes and light
intensities. Aids in detection of damage to sensory visual pathways.
vision. Side vision; vision elicited by stimuli falling on retinal
areas distant from the macula.
(fay-koh-ee-mul-sih-fih-KAY-shun). Surgical procedure. Use
of ultrasonic vibration to shatter and break up a cataract, making
it easier to remove.
(foh-toh-FOH-bee-uh). Abnormal sensitivity to, and discomfort from,
light. May be associated with excessive tearing. Often due to inflammation
of the iris or cornea.
(pin-GWEK-yu-luh). Yellowish-brown subconjunctival elevation composed
of degenerated elastic tissue; may occur on either side of the cornea.
eye." See conjunctivitis.
(prez-bee-OH-pee-uh). Refractive condition in which there is a diminished
power of accommodation arising from loss of elasticity of the crystalline
lens, as occurs with aging. Usually becomes significant after age
(photorefractive keratectomy). Use of high intensity laser light
(e.g., an excimer laser) to reshape the corneal curvature; for correcting
addition lens (PAL), progressive-power lens.. Eyeglass lens
that incorporates corrections for distance vision, through midrange,
to near vision (usually in lower part of lens), with smooth transitions
and no bifocal demarcation line.
retinopathy. See diabetic
(tur-IH-jee-um). Wedge-shaped growth on the bulbar conjunctiva.
May gradually advance onto the cornea and require surgical removal.
Probably related to sun irritation.
(TOH-sis). Drooping of upper eyelid. May be congenital or caused
by paralysis or weakness of the 3rd cranial nerve or sympathetic
nerves, or by excessive weight of the upper lids.
Variable-sized black circular opening in the center of the iris
that regulates the amount of light that enters the eye.
keratotomy (RK) (keh-ruh-TAH-tuh-mee). Surgical procedure.
Series of spoke-like (radial) cuts made in the corneal periphery
to allow the central cornea to flatten, reducing its optical power
and thereby correcting nearsightedness.
Test to determine an eye's refractive error and the best corrective
lenses to be prescribed. Series of lenses in graded powers are presented
to determine which provide sharpest, clearest vision.
error. Optical defect in an unaccommodating eye; parallel light
rays are not brought to a sharp focus precisely on the retina, producing
a blurred retinal image. Can be corrected by eyeglasses, contact
lenses, or refractive surgery.
(RET-ih-nuh). Light sensitive nerve tissue in the eye that converts
images from the eye's optical system into electrical impulses that
are sent along the optic nerve to the brain, to interpret as vision.
Forms a thin membranous lining of the rear two-thirds of the globe.
detachment. Separation of the retina from the underlying pigment
epithelium. Disrupts visual cell structure and thus markedly disturbs
vision. Almost always caused by a retinal tear; often requires immediate
Light-sensitive, specialized retinal receptor cell that works at
low light levels (night vision). A normal retina contains 150 million
canal (shlemz). Circular channel deep in corneoscleral junction
(limbus) that carries aqueous fluid from the anterior chamber of
the eye to the bloodstream.
sclera (SKLEH-ruh). Opaque, fibrous, protective outer layer of the eye
("white of the eye") that is directly continuous with
the cornea in front and with the sheath covering optic nerve behind.
lamp. Microscope used for examining the eye; allows cornea,
lens and otherwise clear fluids and membranes to be seen in layer-by-layer
chart. Test chart used for assessing visual acuity. Contains
rows of letters, numbers, or symbols in standardized graded sizes,
with a designated distance at which each row should be legible to
a normal eye. Usually tested at 20 ft.
(struh-BIZ-mus). Eye misalignment caused by extraocular muscle imbalance:
one fovea is not directed at the same object as the other.
stye. Acute pustular infection of the oil glands of Zeis, located
in an eyelash follicle at the eyelid margin.
meshwork (truh-BEK-yu-lur). Mesh-like structure inside the eye
at the iris-scleral junction of the anterior chamber angle. Filters
aqueous fluid and controls its flow into the canal of Schlemm, prior
to its leaving the anterior chamber.
(TRI-foh-kul). Eyeglass lens that incorporates three lenses of different
powers. The main portion is usually focused for distance (20 ft.),
the center segment for about 2 ft., and the lower segment for near
Normal visual acuity. Upper number is the standard distance (20
ft.) between an eye being tested and the eye chart; lower number
indicates that the tested eye can see the same small standard-sized
letters or symbols as a normal eye at 20 feet.
uveal tract (YU-vee-uh). Pigmented layers of the eye (iris,
ciliary body, choroid) that contain most of the intraocular blood
acuity. Assessment of the eye's ability to distinguish object
details and shape, using the smallest identifiable object that can
be seen at a specified distance (usually 20 ft. or 16 in.).
field. Full extent of the area visible to an eye that is fixating
(VlT-ree-us), vitreous humor. Transparent, colorless gelatinous
mass that fills the rear two-thirds of the eyeball, between the
lens and the retina.
detachment. Separation of vitreous gel from retinal surface.
Usually innocuous, but can cause retinal tears, which may lead to
retinal detachment. Frequently occurs with aging as the vitreous
liquifies, or in some disease states, e.g. diabetes and high myopia.
laser. Laser that produces short pulsed, high energy light beam
to cut, perforate, or fragment tissue.
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