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The
animated description of how the people with myopia see the world
around them.
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A
B C
D E
F G
H I
K L
M N
O P
R S
T U
V W
Y Z |
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Accommodation:
Increase in focusing power of the eye to maintain a clear image
as objects are moved closer. Due to the lens becoming rounder.
Natural loss of accommodation with increasing age is called
presbyopia.
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After-cataract
or secondary cataract:
Remnants of an opaque lens remaining in the eye, or opacities
forming, after extracapsular cataract removal.
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Age-related
macular degeneration or disease
(AMD, ARMD)
(MAK-yu-lur): Deterioration
of the macula affecting people older than 60, resulting in loss
of sharp central vision. The leading cause of legal blindness
in the United States. |
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Amblyopia
(am-blee-OH-pee-uh) or “lazy eye”: Decreased
vision in one or both eyes without detectable anatomic damage
to the retina or visual pathways. Usually uncorrectable by eyeglasses.
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Amsler
grid
(AM-zlur):
Printed grid (black lines on white background) used as a test
for detecting central visual field distortions or defects in
macular degenerations. |
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Angle
or 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. Important for glaucoma.
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Anterior
chamber:
Fluid-filled space inside the eye between the cornea and the
iris.
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Aqueous
(AY-kwee-us) or aqueous humor or aqueous fluid: Clear,
watery fluid that fills the anterior and posterior chambers
of the eye. Nourishes the cornea, iris, and lens and maintains
intraocular pressure.
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Astigmatism
(uh-STIG-muh-tiz-um): A type of refractive error.
Optical defect in which refractive power of an eye is not uniform
in all directions (meridians). Large amount may result in headache
and significant blurring of images.
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Autoimmune
diseases (aw-toh-im-YOON)
or rheumatoid diseases: Chronic, systemic diseases
caused by the immune system’s attack upon some parts of
a patient’s body. Several of these diseases -- rheumatoid
arthritis, Sjögren's syndrome, systemic lupus erythematosus,
and multiple sclerosis -- are associated with serious eye symptoms.
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B
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Background
retinopathy:
See the fact sheet on diabetic retinopathy.
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Bifocals:
Eyeglasses that incorporate two different refractive
powers in each lens, usually for near and distance corrections.
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Binocular
vision:
Blending, by the brain, of the separate images seen by each
eye into one composite image.
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Blepharitis
(blef-uh-RI-tus):
Inflammation of the eyelids, usually with redness, swelling,
and itching.
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Blind
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.
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C
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Canal
of Schlemm: See
Schlemm's Canal.
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Cataracts:
Opacity or cloudiness of the crystalline lens, which may prevent
a clear image from forming on the retina. Surgical removal of
the lens is necessary if visual loss becomes significant, with
lost optical power replaced with an intraocular lens.
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Cataract
extraction:
Removal of a cloudy lens from the eye. Extracapsular cataract
extraction leaves the rear lens capsule intact; with an intracapsular
extraction (usually by cryoextraction) there is complete removal
of the lens with its capsule.
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Central
vision:
An eye's best vision, used for color, reading, and discriminating
fine detail. Results from stimulation of the macular area of
the retina.
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Choroid
(KOR-oyd): Major blood vessel (vascular) layer of
the eye, lying between the retina and the sclera. Provides nourishment
to outer layers of the retina.
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Ciliary
body (SIHL-ee-uh-ree):
A structure near the angle that produces aqueous fluid. See
glaucoma.
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Color
blindness:
Reduced ability to discriminate among colors, especially shades
of red and green. Usually hereditary; much more common in men.
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Cone:
Light-sensitive retinal photoreceptor cell that provides
sharp visual acuity and color discrimination.
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Conjunctiva
(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.
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Conjunctivitis
(kun-junk-tih-VI-tis) or "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.
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Cornea
(KOR-nee-uh): Transparent, dome-shaped front part
of the eye that covers the iris, pupil, and anterior chamber
and provides most of an eye's optical power.
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Corneal
disease: Group
of infections, dystrophies, and injuries affecting the cornea.
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Cross-eyes:
See esotropia.
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Crystalline lens:
See lens.
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D
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Diabetic retinopathy (ret-in-AHP-uh-thee):
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). Leading cause of visual impairment
among working-age Americans. Diabetes also can cause cataracts.
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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 eyedrops containing drugs
(mydriatics) during an eye examination.
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Diopter
(D) (di-AHP-tur): Unit designating the refractive
power of a lens.
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Diplopia,
double vision: Perception
of two images from one object.
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Drusen
(DRU-zin): Tiny, white, shiny deposits behind the
retina. Common after age 60; sometimes an early sign of macular
degeneration.
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Dry eye syndrome
or dry eye: Corneal and conjunctival dryness due
to deficient tear production, predominantly in older women.
Can cause foreign body sensation, burning eyes, and erosion
of conjunctival and corneal epithelium.
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E
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Emmetropia
(em-uh-TROH-pee-uh): Refractive state of having no
refractive error. Images of distant objects are focused sharply
on the retina without the need for either accommodation or corrective
lenses.
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Esotropia
(ee-soh-TROH-pee-uh), cross-eyes: Eye misalignment
in which one eye turns inward (toward nose) while the other
fixates normally.
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Excimer
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.
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Exotropia
(eks-oh-TROH-pee-uh), wall-eyes: Eye misalignment
in which one eye turns outward (away from nose) while the other
fixates normally.
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Extraocular
muscles (eks-truh-AHK-yu-lur):
Six muscles that move the eyeball.
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Eyelids:
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.
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F
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Farsightedness:
See hyperopia.
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Floaters:
Particles that float in the vitreous and cast shadows on the
retina; seen as spots, cobwebs, spiders, etc. Occur normally
in aging and with vitreous detachment, but also pathologically
in retinal tears and inflammation.
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Fluorescein
angiography (FLOR-uh-seen
an-jee-AH-gruh-fee): Diagnostic technique used for
visualizing and recording location and size of eye blood vessels
and any problems affecting them. Fluorescein dye is injected
into an arm vein; then rapid, sequential photographs are taken
of the eye as the dye circulates.
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Fovea
(FOH-vee-uh): Central pit in the macula that produces
sharpest vision. Contains a high concentration of cones and
no retinal blood vessels.
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G
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Glaucoma
(glaw-KOH-muh): Group of diseases, usually characterized
by increased intraocular pressure, resulting in damage to the
optic nerve. A common cause of preventable vision loss. Leading
cause of blindness among black Americans. May be treated by
prescription drugs or surgery. See glaucoma fact sheet on this
website.
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Goblet
cells:
Goblet-shaped cells in the conjunctiva of the eyelids that produce
the mucus of the innermost layer of the tear film.
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H
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Hyperopia
(hi-pur-OH-pee-uh), farsightedness:
Type of 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. Corrected
with additional optical power, which may be supplied by a plus
lens (spectacle or contact).
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I
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IOL
(intraocular lens): Plastic lens that may be implanted,
during cataract surgery, to replace the eye's natural lens.
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Intraocular
pressure (or tension):
Fluid pressure inside the eye. Measured with a tonometer. Usually
abnormally high in Glaucoma.
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Iris
: 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.
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K
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Keratoconus
(kehr-uh-toh-KOH-nus):
Degenerative, hereditary corneal disease affecting vision. Characterized
by generalized thinning and cone-shaped protrusion of the central
cornea, usually in both eyes.
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L
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Lacrimal
gland:
Almond-shaped structure that produces the aqueous (watery) middle
layer of the tear film. Located at the upper outer region of
the eye socket, above the eyeball.
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Laser:
Acronym for Light Amplification by Stimulated Emission of Radiation.
High energy light source to cut, burn, or dissolve tissues for
various clinical purposes: in the retina, to treat diabetic
retinopathy and macular degeneration by destroying 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.
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LASIK
(LAY-sik): Acronym for 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 middle layer of
corneal tissue, producing surgical flattening. Used for correcting
myopia, hyperopia, and astigmatism.
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"Lazy
eye": See
amblyopia.
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Legal
blindness:
Best-corrected visual acuity of 20/200 or worse, or reduction
in visual field to 20 degrees or less, in the better-seeing
eye.
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Lens,
crystalline lens: The eye's natural lens.
Transparent, biconvex-shaped tissue that helps bring rays of
light to a focus on the retina.
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Low
vision:
Term usually used to indicate vision of less than 20/200.
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Low
vision aids:
Instruments such as magnifiers, prisms, print and audio materials,
and computer programs to allow people with low vision to read
and perform other tasks. Help is available even for people who
have lost much of their vision. Visit the National
Eye Institute Web site for more information.
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M
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Macula
(MAK-yu-luh): Small central area of the retina surrounding
the fovea; area of well-resolved, acute, central vision.
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Macular
degeneration:
Retinal diseases in which central vision is lost. Age-related
type (AMD, or age-related macular degeneration) is very common
and affects people over 60. Juvenile macular diseases are hereditary;
they include Stargardt’s disease and Best's vitelliform
macular dystrophy.
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Macular
hole:
A hole in the macula, usually caused by shrinking and pulling
of the vitreous. Treated by surgery.
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Meibomian
glands (my-BOW-mee-uhn)
or tarsal glands: Glands in the conjunctiva of upper
and lower eyelids. Produce the components of the oily, outermost
layer of tear film.
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Myopia
(my-OH-pee-uh), nearsightedness: Focusing defect
in which the eye has too much optical power. 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.
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N
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National
Eye Institute (NEI):
The branch of the U.S. Government's National Institutes
of Health devoted to research on the eye and its diseases. Its
website, www.nei.nih.gov/health,
contains useful, unbiased health information.
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Nearsightedness:
See myopia.
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Neovascularization
(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 and age-related
macular degeneration.
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Nystagmus
(ni-STAG-mus): Involuntary, rhythmic, side-to-side
or up-and-down (oscillating) eye movements that are faster in
one direction than the other.
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O
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Ocular
(AH-kyu-luhr): Pertaining to the eye and vision.
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Ophthalmologist
(ahf-thal-MAH-loh-jist): Physician (MD) specializing
in diagnosis and treatment of refractive, medical and surgical
problems related to eye diseases and disorders.
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Ophthalmoscope
(ahf-THAL-mah-skohp): Diagnostic instrument that
allows the doctor to view the retina.
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Optic
disc or optic nerve
head: Eyeball end of the optic nerve. Denotes the
site of exit of retinal nerve fibers from the eye and entrance
of blood vessels into the eye.
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Optician
(ahp-TISH-un): Professional who makes and adjusts
optical aids, e.g., eyeglass lenses, from refraction prescriptions
supplied by an opthalmologist or optometrist.
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Optic nerve:
Largest sensory nerve of the eye; carries impulses for sight
from the retina to the brain.
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Optometrist
(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.
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P
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Patching:
Covering an amblyopic patient's preferred eye, to improve vision
in the other eye.
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Perimetry
(puh-RIM-ih-tree): A diagnostic test. Method of charting
extent of an eye's field of vision with test objects of various
sizes and light intensities. Aids in detection of damage to
sensory visual pathways.
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Peripheral
vision: Side
vision; vision elicited by stimuli falling on retinal areas
distant from the macula. Images are not well resolved.
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Phacoemulsification
(fay-koh-ee-mul-sih-fih-KAY-shun): Surgical procedure.
Use of ultrasonic vibration to shatter and break up a cataractous
lens, making it easier to remove.
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Photophobia
(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.
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Photoreceptors:
Nerve cells in the retina that are sensitive to light; rods
and cones.
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"pink
eye": See
conjunctivitis.
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Posterior
chamber:
Fluid-filled space inside the eye between the iris and the lens.
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Presbyopia
(prez-bee-OH-pee-uh): Refractive condition in which
there is a diminished ability to accommodate arising from loss
of elasticity of the crystalline lens, as occurs with aging.
Usually becomes significant after age 45.
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Primary
open angle glaucoma
(POAG): The most common type of glaucoma.
Anterior chamber angle (where the cornea and iris meet) is not
plugged; however, aqueous fluid still drains too slowly out
of the eye, causing a rise in intraocular pressure.
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PRK
(photorefractive keratectomy) (foh-toh-ruh-FRAK-tihv ke-ruh-TEK-toh-mee).
Use of high intensity laser light (e.g., an excimer laser) to
reshape the corneal curvature; for correcting refractive errors.
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Progressive
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.
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Proliterative
retinopathy: See
diabetic retinopathy.
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Ptosis
(TOH-sis): Drooping of upper eyelid.
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Pupil:
Variable-sized, circular opening in the center of
the iris that regulates the amount of light entering the eye.
Appears black when looking at eye.
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R
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Radial
keratotomy (RK) (keh-ruh-TAH-tuh-mee):
Type of refractive surgical procedure. Series of spoke-like
(radial) cuts made in the cornea to flatten it, reducing its
refractive power and thereby correcting myopia (nearsightedness).
Mostly replaced by LASIK now.
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Refraction:
A test performed by optometrist or ophthalmologist to determine
an eye's refractive error and the best corrective lenses to
be prescribed. Series of lenses in graded powers are used to
determine which provide sharpest, clearest vision.
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Refractive
error:
Optical defect in an 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 (spectacles),
contact lenses, or refractive surgery.
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Retina
(RET-ih-nuh): Light sensitive neural tissue in the
back of the eye that converts images from the eye's optical
system into electrical impulses. These are sent along the optic
nerve to the brain, which interprets them as vision. The retina
forms a thin, membranous lining of the rear two-thirds of the
eyeball (or globe).
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Retinal detachment: Separation
of the sensory retina from its underlying, supportive, and nourishing
retinal pigment epithelium (RPE) cells. Disrupts vision. Usually
requires immediate surgical repair. Visit the National
Eye Institute Web site for more information.
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Retinal
pigment epithelium (RPE):
Layer of cells behind the sensory retina. Performs
many metabolic tasks for the neural retina.
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Retinitis
pigmentosa (RP):
Set of inherited retinal degenerations. Death of
photoreceptors gradually leads to night-blindness and to loss
of peripheral vision, causing tunnel vision.
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Retinopathy
of prematurity (ROP):
Retinal disease seen in some low-birthweight, premature babies.
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Rod:
Light-sensitive, specialized retinal receptor cell that works
at low light levels for night vision. A normal retina contains
150 million rods.
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S
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Schlemm's
Canal (shlemz):
Circular channel deep in corneoscleral junction (limbus) that
carries aqueous fluid from the anterior chamber of the eye to
the bloodstream. Important for glaucoma.
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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.
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Sjögren’s
syndrome:
Autoimmune disease affecting mostly women, in which glands producing
tears and saliva are attacked. Causes severe dry eye. For more
information, see http://www.sjogrens.org/.
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Slit
lamp:
Microscope used for examining the eye; allows cornea, lens,
and otherwise clear fluids and membranes to be seen in layer-by-layer
detail.
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Snellen
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.
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Stargardt’s
disease (STAHR-gahrts):
Most common type of juvenile macular degeneration.
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Strabismus
(struh-BIZ-mus): Eye misalignment caused by extraocular
muscle imbalance; one fovea is not directed at the same place
in a scene as the other.
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Sty
or stye: Acute, bacterial, pustular infection of
oil glands located in an eyelash follicle at the eyelid margin.
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T
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Tear
film:
Layered film on the surface of the cornea that keeps the eye
lubricated.
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Tonometer
(tow-NAH-muh-tuhr): Instrument used to measure intraocular
pressure.
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Trabecular
meshwork (truh-BEK-yu-lur):
Mesh-like, spongy structure inside the eye at iris-scleral junction
of anterior chamber angle. Filters aqueous fluid and controls
its flow into Canal of Schlemm's, prior to its leaving the anterior
chamber. Often becomes partially blocked in glaucoma.
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Trifocal
(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 vision (14 in.).
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20/20:
Normal visual acuity. Upper number is the standard
distance (in feet) between an eye being tested and the Snellen
eye chart; lower number indicates that a line of letters or
symbols of a specific size can be read from 20 feet away.
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U
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Usher’s
syndrome:
Inherited condition that causes serious hearing loss plus retinitis
pigmentosa (RP). Symptoms usually present at birth or shortly
thereafter.
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Uvea
or uveal tract (YU-vee-uh): Pigmented layers of the
eye (iris, ciliary body, choroid) that contain most of the intraocular
blood vessels. Site of uveitis, a serious inflammation
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V
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Visual
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 feet).
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Visual
field:
Full extent of the area visible to an eye that is fixating straight
ahead.
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Vitreous
(VlT-ree-us) or vitreous humor or vitrous body: Transparent,
colorless, gelatinous mass that fills the rear two-thirds of
the eyeball, between the lens and the retina.
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Vitreous
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.
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W
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Wall-eyes:
See exotropia.
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Y
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YAG
laser:
Laser
that produces short pulsed, high-energy light beam to cut, perforate,
or fragment tissue.
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Z
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Zonules:
Small fibers that hold the lens in place. The degree of tension
in them changes the shape of the lens.
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Eye
Tests