Eye Care Glossary

Accommodation

The eye’s ability to adjust its focus
from distant to near objects. This process is achieved
by the lens changing its shape. 

Acuity

The clearness of eyesight; the keenness
of the visual powers. AKA: Visual
Acuity

Age-Related
Macular Degeneration (ARMD, AMD or ARM)

A major cause of central vision loss
which, in about 70% of the cases, is associated with
aging and the breakdown of the retinal structures
at the macula

Albinism

Congenital deficiency or absence of
pigment (color) in the skin, hair, choroid,
retina and iris.

Amaurosis

Blindness.

Amblyopia

Sometimes referred to as lazy
eye
, a condition of diminished visual
acuity
 in the absence of any detectable anatomic
or physiologic cause. 

American
National Standards Institute (ANSI) Z87.1

The American National Standards Institute’s
Practice for Occupational and Educational Eye and
Face Protection; eyewear that meets this standard
is considered safer than eyewear that does not. 

Ametropia

Defective vision that is correctable
by eyeglasses or contact lenses.

Aniseikonia

A condition in which the image sizes
in each eye are different, leading to difficulties
in achieving single vision. Symptoms of aniseikonia
are headaches and dizziness.

Anisocoria

Different-sized pupils in each eye.

Anisometropia

Greek meaning “not the same correction,”
anisometropia is when there is a significant difference
in correction between the two eyes. This may cause
eye strain and double vision (diplopia).

Anterior
Chamber

The space in front of the iris
and behind the cornea.

Antimetropia

One eye nearsighted; the other farsighted.

Anti-Reflective
Coating

Anti-reflective coatings reduce glare
and enhance your appearance by removing distracting
reflections.

Aphakic

Condition of the eye with crystalline
lens
 removed. Also refers to post-cataract patients
who have had cataract surgery.

Aqueous
Humor

Also known as aqueous fluid: clear,
watery fluid that flows between and nourishes the
lens and the cornea.

Arteriosclerosis

A chronic disease of the arteries
characterized by the thickening or hardening of the
arterial walls impairing blood circulation.

Asthenopia

A group of symptoms generally referred
to as “eye-strain.” Included are: headaches,
tearing, “tired eyes,” itching, burning
and blurred vision.

Astigmatism

A condition that occurs when the front
surface of the eye (the cornea) is slightly irregular
in shape. This irregular shape prevents light from
focusing properly on the back of the eye (the retina).
As a result, vision may be blurred at all distances.

Bifocal
Lens

Lens with two focal lengths, one for
distance and one for near. Usually the distance correction
is on top and the correction for near is on the bottom.

Blended
Lens

While traditional multifocal
lenses
 have a line in the middle of the lens,
blended lenses (progressive
lenses
) are line-free. The power gradually changes
from distance correction to intermediate vision (at
arm’s length), to near vision (at reading distance),
moving invisibly from the top to the bottom of the
lens.

Blind
Spot

(1) A small area of the retina
where the optic nerve enters
the eye; occurs normally in all eyes. (2) Any gap
in the visual field corresponding to an area of the
retina where no visual cells
are present. 

Cataract

A cataract is a clouding of part or
all of the lens inside the eye, resulting in blurred
or distorted vision. 

Cataract
Lens

Eyeglass lens
used following cataract removal.
Cataract lenses were once widely used for post-cataract
patients; however, IOL (interocular) lenses are now
the most commonly used replacement for the removal
of the crystalline lens,
eliminating the necessity for cataract lenses. 

Cathode
Ray Tube (CRT)

The monitor or display screen of a
computer. Special computer eyeglasses are available
to increase or enhance vision while viewing computer
screens.

Choroid

The layer in the eye filled with blood
vessels that nourishes the retina.

Chromatic

Of or pertaining to color.

Ciliary
Muscle

The eye’s focusing muscle that allows
the crystalline lens
to perform its function of accommodation.

Coloboma

A defect of the iris
caused by a failure of the eyeball to fuse properly
during fetal development. These are developmental
anomalies and do not worsen as the child grows older.

Color
Blindness

Also known as color deficiency, the
inability to recognize colors.

Computer
Vision Syndrome (CVS)

The variety of eye and vision-related
problems associated with prolonged computer use. CVS
is characterized by eyestrain, blurred vision, headaches
and dry or irritated eyes.

Conjunctiva

The thin, moist tissue that lines
the inner surfaces of the eyelids and the outer surface
of the sclera (the outer layer
of the eyeball).

Conjunctivitis

Inflammation of the conjunctiva,
often referred to as “pink eye.”

Contact
Lens

A thin, bowl shaped lens worn on the
surface of the eye.

Contact
Lens Drops

Eye drops for contact lens wearers;
regular eye drops can discolor contact lenses. 

Contrast
Sensitivity

The ability to perceive differences
between an object and its background.

Convergence

Simultaneous turning in of both eyes
to keep objects in sight as they approach the eyes

Cornea

Serving to transmit light to the eye,
the cornea is a transparent tissue that covers the
front surface of the eye.

Corneal
Abrasion

A cut or scratch on the cornea

Corneal
Implants

Devices (such as rings or contacts)
placed in the eye, usually to correct vision.

Corneal
Ring

A type of vision correction surgery
where a doctor inserts a tiny plastic ring into the
cornea (which lets light into
the eye), reshaping the cornea and helping it to focus
light better onto the retina
to improve vision. The ring can be adjusted and even
removed if desired. 

Corneal
Topography

Mapping or examination of the cornea.
The information gathered is useful to evaluate and
correct many eye conditions.

Corneal
Ulcer

A wound in the outer layer of the
cornea caused by injury, dryness
due to lack of tear production or infection.

Crossed
Eyes

A misalignment of the eyes where one
or both eyes point inward, toward the nose.

Crystalline
Lens

The crystalline lens is the lens of
the eye, serving to focus light on the retina,
and changing its shape allows one to focus at near
or far distance.

Dacryostenosis

A blocked tear
duct
, which is characterized by a lot of tearing.

Daily
Wear Contact Lens

Soft contact lenses worn every day
for six months up to a couple of years, requiring
daily cleaning and disinfecting, as well as a periodic
enzymatic soak (usually once a week).

Depth
Perception

The ability to judge the distance
and/or spatial relationship of objects of varying
distances. 

Diabetes

A chronic, metabolic disorder where
a lack of insulin secretion and /or increased cellular
resistance to insulin results in elevated blood levels
of glucose. Complications due to diabetes can include
damage to the eyes, kidneys, nervous system and vascular
system. 

Diabetic
Retinopathy

A complication of diabetes
that is triggered by damage to the blood vessels of
the eye. 

Dilate

A process by which the pupill
is temporarily enlarged with special eye drops. This
allows an eye doctor to see more of the retina
and look for signs of diabetic retinopathy and other
eye diseases or health concerns. After the exam, close-up
vision may remain blurred for several hours. 

Diopter

A diopter is a unit of measure for
expressing the magnifying power of a lens or lens
system. A one diopter lens has a focal distance of
one meter. A two diopter lens has a focal distance
of one-half meter.

Diplopia

Also known as double vision, a visual
disorder due to unequal action of the eye muscles
causing two images of a single object to be seen.

Disposable
Contact Lens

Contact lenses that are thrown away
after a short period of time. Usage of disposable
contact lenses ranges from one day to two weeks, while
frequent replacement lenses are discarded monthly
or quarterly. Go to Top
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Divergence

Simultaneous turning out of both eyes
to keep sight of an object as it moves farther from
the eyes.

Dominant
Eye

The eye that “leads” its
mate during eye movements.

Double
Bifocal Lens

An occupational
lens
 with a bifocal on the bottom and the top
of the lens. 

Dye

A color that is absorbed into a plastic
lens
.
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Edge
Coating

Lens edges can be painted or color-treated
to disguise thick edges of lenses or to coordinate
with frame color for cosmetic reasons.

Edge
Polish

Both glass and plastic
lens
 edges can be polished to a high luster resulting
in clear and shiny lens edges. This option is often
chosen with rimless frames to disguise the edges of
the lenses, especially if they are thicker. 

Endothelium

The cornea’s inner layer of cells.

Enzymatic
Cleaner

Used for contact lenses, a cleaner
that removes protein deposits and other debris. It’s
recommended for use either daily, weekly, or monthly.
Some enzymatic cleaners are a small tablet dropped
into a solution along with the lens; others come in
liquid form.

Epithelium

The cornea’s outer layer of cells.

Esotropia

The turning inward of the eye.

Executive
Lens

Bifocal or trifocal that extends across
the full width of the lens. Executive lenses offer
the advantage of wide field of vision in reading area.

Exotropia

The turning outward of the eye

Extended
Wear Contact Lens

Contact lenses that are worn without
removal for up to seven days.

Eye
Care Doctor

Optometrists
(O.D.s) and ophthalmologists
(M.D.s).

Faceted
Lens

Polished, beveled edge lens put in
a rimless frame. 

Farsightedness

Also known as Hyperopia,
the inability to see objects up close. It is the result
of an eyeball that is too short or whose outside surface
(the cornea) is too flat. The exact cause is not known,
although farsightedness may be inherited. 

Floaters

Cells and fragments of debris in the
eye that pass across your field of vision.

Focal
Length

Distance from the optical center of
the back surface of the eye to the principal focus
of the lens. 

Focus

The point at which light rays through
a lens form an image.

Fovea

A depression in the retina
that contains only cones (not rods),
and that provides acute eyesight.

Frequent
Replacement Contact Lens

Any contact
lens
 that is thrown away after a moderately short
period of time, anywhere from one day to two weeks
(disposables) to monthly or quarterly (frequent replacement).

Fundus

The interior lining of the eyeball,
including the retina, optic
disc, and macula. This portion
of the inner eye can be seen during an eye exam by
looking through the pupil.

Ghost
Image

Often referred to when describing
the benefits of anti-reflective
coatings
, the internal reflections from the lens
surfaces. Ghost images are mostly experienced at night.

Glass
Lens

The most scratch-resistant lens material.
Heavier than plastic lenses,
glass comes in a wide selection of lens styles and
can be ordered with absorptive and photochromic tints.

Glaucoma

An eye disease in which the passages
that allow fluid in the eye to drain become clogged
or blocked, or there is too much fluid produced inside
of the eye. Increased pressure inside the eye then
damages the optic nerve
and causes vision loss.

Gonioscopy

Use of a special contact
lens
 to look at the eye’s aqueous drainage area.
This can be thought of as looking at the drain of
the eye to see if it’s plugged up.

Gradient
Tinting

Usually applied for cosmetic purposes,
gradient tinting is darker at the top of the lens
than in the middle and lightest at the bottom.

Graves’
Ophthalmopathy

Thyroid-related, autoimmune eye disorder
usually associated with Graves’ disease; symptoms
include eyelid retraction, bulging eyes, light sensitivity,
discomfort, double vision and vision loss.

Gross
Visual Fields

A brief 5 to10 minute test in which
the doctor examines your peripheral (side) vision.
The test can be conducted using specialized equipment
or simply by having you follow a focal point. 

Hard
Contact Lens

Small, hard contact
lenses
. Compared with soft and rigid lenses, hard
contact lenses are less
healthy to wear long-term, since the material doesn’t
allow oxygen to reach the surface of the eye.

High
Blood Pressure (Hypertension)

Abnormally high arterial blood pressure.

High
Index Lens

A thinner and lighter lens in either
glass or plastic, chosen for lightweight comfort and
attractiveness. 

Hyperopia

Also know as farsightedness,
the inability to see objects up close. It is the result
of an eyeball that is too short or whose outside surface
(the cornea) is too flat. The exact cause is not known,
although farsightedness may be inherited.
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Hypotropia

A turning downward of one eye.
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Intermediate
Zone

Refers to the middle zone of sight.
Considered to be an arm’s length, the top trifocal
segment in a multifocal lens corrects vision for this
distance. 

Interpupillary
Distance

Commonly referred to as PD, the distance
between your pupils. 

Intraocular
Lens (IOL)

A lens implanted during cataract
surgery to replace a damaged lens.

Intraocular
Pressure (IOP)

Pressure inside the eye.

Iris

The colored ring of tissue suspended
behind the cornea and immediately
in front of the lens. It regulates the amount of light
entering the eye by adjusting the size of the pupil.

Jaeger
Test

Measurement of visual
acuity
 at the reading distance.

Keratitis

Inflammation of the cornea. Keratitis
may be deep, when the infection causing it is carried
in the blood or spreads to the cornea from other parts
of the eye, or superficial, caused by bacterial or
viral infection or by allergic reaction. Burns of
the cornea, such as those produced by chemicals or
ultraviolet rays, also give rise to a form of keratitis.

Keratoconus

A degenerative corneal disease in
which the center of the cornea
thins and the cornea becomes
conical, rather than spherical, in shape.

Keratometry

Assessing the eye’s shape to check
for astigmatism.

Lacrimal
Gland

The small, almond-shaped structure
that produces tears, it is located just above the
outer corner of the eye.

Lateral
Rectus Muscle

Muscle that moves the eye away from
the nose.

Laser
In-Situ Keratomileusis (LASIK)

A medical procedure in which a doctor
uses an excimer laser to reshape the cornea
under a flap of corneal tissue. 

Lazy
Eye

Also know as Amblyopia,
a condition of diminished visual
acuity
 in the absence of any detectable anatomic
or physiologic cause. 

Legal
Blindness

In the United States, (1) visual
acuity
 of 20/200 or worse in the better eye with
corrective lenses (20/200 means that a person must
be at 20 feet from an eye chart to see what a person
with normal vision can see at 200 feet), or (2) visual
field restricted to 20 degrees diameter or less (tunnel
vision) in the better eye. 

Lens

(1)The transparent structure in the
front of the eye. With outward curves on both sides,
the lens helps focus light on the retina.
(2)A piece of glass or other transparent material
having two polished opposite surfaces, at least one
of which is curved. 

Lens-Aphakic

A spectacle lens worn after cataract
surgery when an intra-ocular lens implant is not put
into the eye after the cataract
is removed. 

Lensometer,
vertometer

Instrument used to measure the power
of a spectacle lens. 

Lenticular
Lens

Used primarily for post-cataract lenses,
a lenticular lens is one in which the power is in
the center of the lens but the edge is a portion of
plain glass, so it is easily mounted in a frame. Lenticular
lenses are designed to reduce the weight and thickness.