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20/20 vision

Normal visual acuity; upper number is the standard distance between the tested eye and the eye chart, and the lower number is the distance at which the tested eye can see the same standard-sized letters as a normal eye at 20 feet



Eye rotation away from the midline


Blurred or distorted image quality resulting from the physical properties of an optical device (ie, lens)


The eye’s increase in optical power in order to maintain image clarity as objects are moved closer


Refers to the extent to which a patient follows a doctor’s treatment regimen without close supervision

Adjunctive therapy

Additive treatment or medication that enhances the benefit of another treatment or medication

Age-related macular degeneration

Group of conditions that include deterioration of the macula, resulting in a loss of sharp central vision; the most common cause of decreased vision after 50


Lack of tear production


Lack of pigment in the eyes, hair, and skin, which is usually associated with decreased visual acuity


An antigen that creates an allergic or hypersensitivity response

Allergic conjunctivitis

Inflammation of the conjunctiva from hypersensitivity to allergens

ALT surgery

Argon laser trabeculoplasty; surgical procedure that uses a laser to create small burns in the trabecular meshwork to lower intraocular pressure


“Lazy eye”; decreased vision in one or both eyes without anatomical defects detected in the retina or visual pathway


Instrument used in evaluation and treatment of strabismus and other binocularity problems

Angle-closure glaucoma

Rise in intraocular pressure due to aqueous fluid behind the iris being unable to pass through the pupil; patients with anatomically narrow angles are predisposed to this condition


Loss of vision, particularly to part of the visual field

Anterior chamber

Space between the iris and innermost corneal surface that is filled with fluid


Absence of the eye’s crystalline lens, such as after cataract extraction

Applanation tonometer

Instrument that flattens the cornea to measure intraocular pressure

Aqueous humor

Clear fluid that fills the space in the eye between the cornea and the lens; maintains intraocular pressure and provides nourishment to the cornea, iris, and lens

Aqueous outflow

Passage of aqueous fluid through the anterior chamber angle structures

Artificial tears

Eyedrops with similar consistency to natural tears to alleviate Dry Eye symptoms


Refractive error that prevents the eye from focusing sharply, usually resulting from an abnormally shaped corneal surface; correctable by eyeglasses, contact lenses, or refractive surgery


Bacterial conjunctivitis

Inflammation of the conjunctiva caused by a bacterial infection; usually contagious

Basal lamina

Innermost layer of the choroid, directly under the retina; damage to the basal lamina is responsible for many bleeding disorders of the macula area

Bell’s palsy

Condition in which muscles of the brows, eyelids, and mouth are paralyzed by damage to the 7th cranial nerve; may cause affected eyelids to remain open, resulting in corneal drying


Twice daily


Eyeglasses that incorporate lenses of 2 different powers; allows for both near and far distance sight without changing eyewear


Referring to or affecting both eyes


Flap of tissue created to cover a sclero-corneal drainage channel during glaucoma surgery; enhances fluid outflow from the eye


Inflammation of the eyelids; may be caused by infection or allergy


Inflammation of the conjunctiva


Any plastic surgery of the eyelids; often cosmetic


Sudden, involuntary spasm causing uncontrolled blinking and squeezing of the eyelid

Blind spot

Nonseeing area within every visual field; caused by absence of photoreceptors where the optic nerve enters the eye


Inability to see

Blink reflex

Periodic contraction of the eye muscles approximately every 5 seconds, causing the eyelid to close over the eye, spreading tears over the eye and limiting light entering the eye



Incision to remove part of the lens capsule

Cat dander

The result of the normal shedding of cat hair or coat that can cause an allergic response in certain people


Opacity and cloudiness of the lens, preventing a clear image from being formed on the retina; removal may be necessary if vision is affected significantly; caused by age, trauma, or disease

Central retinal artery

First branch of the ophthalmic artery; provides nutrients to the inner two-thirds of the retina

Central retinal vein

Collects retinal venous blood drainage and exits through the optic nerve


Inflamed bump in the eyelid’s meibomian gland


Swelling of the conjunctiva


Vascular layer of the eye between the retina and sclera, providing nutrients to the outer layers of the retina


Inflammation of the choroid

Chronic Dry Eye

Corneal/conjunctival dryness due to deficient tear production and/or increased tear evaporation; keratoconjunctivitis sicca, Dry Eye syndrome

Ciliary body

Tissue in the eye that is involved in lens accommodation, intraocular pressure control, and producing the aqueous humor

Color blindness

Reduced ability to differentiate between colors, especially reds and greens; usually hereditary


Refers to a patient following a doctor’s treatment regimen


Light-sensitive cell of the retina that allows for sharp visual acuity and color detection

Congenital glaucoma

High intraocular pressure, hazy corneas, and large eyes in children from newborn to 6 months old; developmental abnormalities prevent normal fluid drainage from the eye; requires surgical intervention


Mucous membrane covering the outer surface of the eyeball (except the cornea) and inside surface of the eyelids

Conjunctival hyperemia

Redness of the conjunctiva; associated with all types of conjunctivitis

Conjunctival sac

Pocket of conjunctiva between the upper eyelid and eyeball and lower eyelid and eyeball that permits the eyeball to rotate freely


Inflammation of the conjunctiva; usually viral and can be contagious

Contact lens

Small disc worn on the cornea or sclera, providing visual correction of refractive errors


Moving both eyes toward each other to maintain single binocular vision of an approaching object


Displacement of the pupil from its normal position


Transparent front of the eye covering the iris, pupil, and anterior chamber; provides the bulk of the eye’s optical power

Corneal abrasion

Scraped area of the cornea accompanied by superficial tissue loss

Corneal apex

Central 3-5 mm where the cornea has the greatest curvature

Corneal edema

Hazy and swollen cornea

Corneal erosion

Loss of the outer layer of the cornea because it fails to adhere to the Bowman’s membrane

Corneal staining

Use of dye such as fluorescein to reveal corneal epithelial defects

Corneal transplant

Replacement of damaged or diseased cornea with donor corneal tissue


Steroid used to treat inflammatory and allergic diseases


Optic cup; depression in the center of the optic disc that normally occupies less than one-third of the disc diameter

Cup-to-disc ratio

Evaluates the progression of glaucoma by indicating the percentage of the disc occupied by the optic cup

Cupped disc

Abnormal enlargement of the optic cup, usually due to a long-term increase in intraocular pressure

Cylinder correction

Use of a lens that produces different refractive power in each meridian; used to correct astigmatism

Cystoid macular edema

Retinal swelling and cyst formation in the macular area, can result in temporary or permanent decrease in vision



Inflammation of the tear sac, often associated with poor tear drainage

Depth perception

Awareness of relative spatial location of objects; perception of nearness and farness

Diabetic macular edema

The leaking of retinal blood vessels into the macula in patients with diabetes, causing the macula to swell, which can temporarily or permanently decrease central vision

Diabetic retinopathy

Progressive retinal changes that accompany diabetes mellitus; this can progress from background retinopathy to proliferative retinopathy, which includes abnormal new blood vessels and fibrous tissue development


Widening of the pupil


Unit of measurement of the refractive power of a lens


Perception of two images from one object; double vision


Optic disc; ocular end of the optic nerve

Dry Eye

Corneal/conjunctival dryness due to deficient tear production and/or increased tear evaporation


Distorted shape of pupil


Epicanthal fold

Vertical skin fold at each side of the nose; hides the caruncle; present in infants before nose bridge is developed


Overflow of tears down the face caused by poor tear drainage, excessive tearing, or outward turning of the lower eyelid


Abnormal skin redness caused by capillary congestion under the skin


Eye misalignment in which one eye turns inward while the other stays fixed straight ahead


Procedure that removes the contents of the eyeball, leaving behind the sclera shell and, sometimes, the cornea; usually for reducing pain in a blind eye


Eye misalignment in which one eye turns outward while the other stays fixed straight ahead

Exposure keratitis

Corneal irritation or inflammation caused by corneal drying due to incomplete closure of the eyelid

External diseases

Diseases that affect the cornea, sclera, conjunctiva, or eyelids


Sense organ for sight


One of the stiff hairs at the margin on the eyelid


Structure covering the front of the eye that protects it, limits the light entering in, and distributes the tear film over the corneal surface


The sclera and the cornea



Refractive error that allows the eye to see clearly at a distance, but close-up images are blurred; hyperopia

Femtosecond laser

Short-pulse laser that is used to create corneal flaps in refractive surgery


Particles that float in the vitreous, casting shadows on the retina and appearing as spots


Colored dye that illuminates; used on the cornea to identify damage

Focal point

Position on the principal axis of a lens system where parallel light rays are brought to a point of focus


Tiny elevations on the undersurface of the eyelids; associated with viral conjunctival inflammation

Foreign body sensation

The feeling of something in the eye; can be caused by an actual foreign body in the eye or by various damage or conditions


The central part of the macula that produces the sharpest vision


Interior posterior surface of the eyeball which includes the retina, optic disc, macula, and posterior pole


Generic drug

A drug that has gone off patent and is produced by any number of manufacturers; according to the FDA, generic drugs are copies of brand-name drugs and are the same dosage form, safety, strength, route of administration, quality, performance characteristics, and intended use


Degenerative change that produces a white ring-shaped deposit of fat near the peripheral edge of the cornea; typically in patients over 60

Glare test

Clinical test that determines the extent to which a bright light shined in the eye changes visual acuity; evaluates the degree of visual impairment caused by a cataract


Group of ocular diseases characterized by increased intraocular pressure that results in optic nerve damage, affecting visual field


The eyeball; a sensory organ that uses light to transmit visual information to the brain; 3 major layers in the globe include corneo-sclero, uvea, and retina

Goblet cell

Large mucous glands in the conjunctiva that secrete mucin, a component of precorneal tear film; can be damaged in Dry Eye syndrome


Test that examines the anterior chamber angle structures through a special lens with a slit lamp


Surgical procedure that is often used to treat congenital glaucoma; it consists of an incision in the trabecular meshwork

Graves disease

Symptoms of the eye that may result with excessive thyroid-related concentration, including eyelid retraction, eyelid lag, corneal drying, and optic nerve inflammation



Hazy ring seen around lights; can be a sign of a refractive error or optical defect such as cataract

Herpes keratitis

Eye infection caused by the herpes simplex virus. Results in inflammation and ulcers

Heterochromia of the iris

Having a different color iris in each eye


Chemical that creates an allergic or inflammatory response


Acute infection of oil glands of the eyelid; externally, also known as a stye; internally (in the meibomian glands), also known as a chalazion, if chronic


Clinical sign; increased blood flow; usually refers to eye redness due to increased blood flow to the conjunctival blood vessels


Refractive error in which an underpowered eye is too short for its optical power; farsightedness


Functional defect in which one eye deviates upward while the other remains straight and fixates normally


Clinical sign; blood in the anterior chamber, often following blunt trauma to the eyeball


Functional defect in which one eye deviates downward while the other remains straight and fixates normally


Intraocular lens

Lens that may be surgically implanted to replace the eye’s natural lens

Intraocular pressure (IOP)

The pressure of fluid within the eye; elevated IOP is a treatable risk factor for glaucoma


Removal of a portion of iris tissue


Pigmented tissue behind the cornea that gives the eye its color and allows light to enter the eye by controlling the size of the pupillary opening; part of the uveal (middle) layer of the eye


Inflammation of the iris, causing pain, tearing, blurring, small pupil, and red congested eye


Equal vision in both eyes



Surgical removal of corneal tissue


Corneal inflammation; can be caused by a variety of infections, injuries, and unknown causes

Keratoconjunctivitis sicca

Corneal and conjunctival dryness due to deficient tear production and/or increased tear evaporation; Dry Eye syndrome


Corneal melt; superficial corneal layers that "melt" away; often associated with severe inflammation, Dry Eye, or rheumatoid arthritis


Surgical procedure on the cornea that usually refers to a corneal graft (replacing damaged corneal tissue with donor tissue)


Any incision into the cornea (surgical procedure)


Lacrimal gland

Almond-shaped gland located above the eyeball in the upper outer region that produces tears


Tear production; crying


Acronym for Light Amplification by Stimulated Emission of Radiation; a high-energy light source that can cut, burn, or dissolve tissues for clinical procedures; used in many eye care procedures such as refractive surgery, treatment of diabetic retinopathy and macular degeneration, and removal of trabecular meshwork in glaucoma patients


LAser in Sltu Keratomileusis; refractive surgery in which the cornea is reshaped to change its optical power; corrects myopia, hyperopia, and astigmatism

Legal blindness

Visual acuity of 20/200 or less, or visual field reduction to 20 degrees or less (in the better eye)


Any transparent material (often glass) that can bend light rays predictably


Removal of the eye’s natural lens


Area where the cornea joins the sclera and the bulbar conjunctiva attaches to the eyeball

Low-tension glaucoma

Normal-tension glaucoma; type of open-angle glaucoma in which a patient exhibits signs such as progressive disc cupping and visual field loss, but with normal intraocular pressure



Distorted vision in which objects appear larger than normal


Central area of the retina; provides central vision used for reading and seeing fine detail

Macular degeneration

Group of conditions that include degeneration of the macula; results in loss of sharp central vision

Macular edema

Retinal swelling and cyst formation in the macula; can temporarily or permanently decrease vision


Abnormality of the macula


Loss of eyelashes often caused by chronic blepharitis


Increased image size created through the use of optical devices

Meibomian gland

Oil gland in the eyelid tissue that secretes the outer portion of the tear film; prevents rapid tear evaporation and tear overflow

Microbial keratitis

Corneal infection from overuse of contact lenses; caused by microorganisms

mm Hg

Millimeters of mercury; units used to measure intraocular pressure

Moll glands

Sweat glands near the eyelash follicles; infection can cause a stye


Referring to one eye


Refractive error caused by an overpowered eye, which has too much optical power for its length; nearsightedness


Narrow-angle glaucoma

Rise in intraocular pressure caused by narrow anterior chamber angles that prevent aqueous drainage

Nasolacrimal duct

Tear drainage channel from the lacrimal sac to the mucous membrane of the nose

NDC number

US National Drug Code; a standard code used to identify FDA-approved drugs and biologicals


Refractive error that allows the eye to see close-up objects clearly, but distance vision is blurred; myopia

Neurotrophic keratitis

Corneal inflammation resulting from trauma or damage to corneal nerves; leads to cornea anesthesia

Night blindness

Poor visual adaptation to the dark, resulting in reduced vision in low light; usually indicates defect in retinal rods

Normal-tension glaucoma

See low-tension glaucoma


A functional defect in which the patient displays involuntary oscillating eye movements that are faster in one direction than the other


Ocular biometry

Test that measures distance between various ocular structures (usually with A-scan or B-scan ultrasound instruments)

Ocular hypertension

Elevated IOP, but with no evidence of optic disc or visual field changes; potential (but not definite) glaucoma suspect

Ocular Surface Disease Index© (OSDI©)

A valid and reliable instrument of 12 questions for measuring Dry Eye Disease and its effect on vision-related function


Right eye

Open-angle glaucoma

The most common type of glaucoma caused by the slowing of normal aqueous outflow from the eye; can result in gradual, irreversible vision loss

Ophthalmic medical assistant

Certified allied health professional in ophthalmology; three levels are certified by JCAHPO®: COA®, COT®, and COMT®


Doctor of medicine (MD) or doctor of osteopathic medicine (DO) specializing in diagnosis and treatment of eye diseases and disorders.


Medical specialty dealing with function and diseases of the eye


Use of an ophthalmoscope to examine the internal structures of the eye

Optic nerve

The second cranial nerve that is the largest sensory nerve of the eye; carries sight information from the retina to the brain for processing

Optic neuropathy

Abnormality or degeneration of the optic nerve, not due to inflammation


Vision care professional who makes and adjusts optical aids such as eyeglasses


Doctor of optometry (OD) who specializes in vision problems and treatments


Vision care specialty that deals with the detection and management of ocular disease


Socket; cranial cavity of the skull that contains the eyeball


Left eye

Outflow (aqueous)

Passage of aqueous fluid out of the eye through the anterior chamber angles



Test to measure corneal thickness

Palpebral fascia

Fibrous membrane that forms a protective layer between the eyelid and the bony orbit (socket)

Perennial allergies

Also known as year-round allergies, these are likely due to indoor allergens such as pet dander.


Area surrounding the eyeball

Peripheral vision

Side vision, created by stimuli falling on retinal areas that are far from the macula


Surgical procedure that uses ultrasound vibration to break up a cataract, making it easy to suction out of the eye


Refers to an eye that has its natural lens


Abnormal sensitivity to light; associated with discomfort and excessive tearing; often due to iritis or keratitis


Sensation of light or flashes from mechanical or electrical irritation of the retina (not from a light stimulus)

Photorefractive keratectomy (PRK)

Refractive surgery that reshapes the corneal curvature with a laser after the surface of the cornea has been removed

Pink eye

Conjunctivitis; inflammation of the conjunctiva that is usually viral in origin; symptoms include discharge, grittiness, redness, and swelling


Microspores of seed plants that can induce allergic or hypersensitivity reactions in some people

Posterior capsular opacification

After cataract surgery, the rear lens capsule can cloud over; needs removal to improve vision

Posterior chamber

Space between the back of the iris and the front of the vitreous


Loss of power of accommodation due to the decline in elasticity of the crystalline lens or ciliary muscle function (occurs with aging), causing age-related blurry near vision in adults

Primary open-angle glaucoma

The most common type of glaucoma caused by the slowing of normal aqueous outflow from the eye; can result in gradual vision loss


As needed (as medication dosing)




Unknown deposits appearing on the lens surfaces and other ocular structures; often associated with high intraocular pressure


Sagging upper eyelid

Puff tonometer

Device that measures intraocular pressure by blowing a puff of air against the cornea to flatten it

Punctal plug

Plastic plug inserted into the punctum to prevent tear drainage, preserving tears to keep the eye moist

Punctate keratitis

Corneal disease characterized by small corneal lesions of unknown origin


Black circular opening in the center of the iris that varies in size to regulate the amount of light that enters the eye



Once daily


Four times daily



Bending of light as it travels from a medium of one density to another medium of another density

Refractive error

Optical defect in an unaccommodating eye; correctible with surgery, eyeglasses, or contact lenses


Light-sensitive tissue in the eye that converts images into electrical impulses that are sent to the brain via the optic nerve to interpret as vision

Retinal detachment

Separation of the retina from the underlying pigment epithelium; usually caused by a retinal tear that leaks fluid from the vitreous and separates the retina

Retinal vein occlusion

Blockage of blood flow through the central retinal vein, causing a decrease in vision


Inflammation of the retina


Malignant tumor that develops from retinal visual cells


Any noninflammatory degenerative disease of the retina


Test that measures the eye’s refractive error


Specialized retina cell that is a light-sensitive receptor in low-light levels


Schirmer test

Measures tear production with filter paper strips

Schlemm’s canal

Channel in the corneo-scleral junction that carries aqueous fluid from the anterior chamber to the bloodstream


Opaque protective outer layer of the eye (“the white”) that connects to the cornea and the sheath of the optic nerve


Inflammation of the sclera, often painful

Seasonal allergies

Allergies, such as a ragweed allergy, that are seasonal in nature (eg, springtime or fall)

Sjögren syndrome

Chronic autoimmune disease often characterized by dry eyes, dry mouth, and arthritis

Slit lamp

Microscope used to examine the eye; shows the cornea, lens, and clear fluids and membranes in layered detail

SLT surgery

Surgical procedure in which a laser is used on the trabecular meshwork to increase aqueous outflow, reducing intraocular pressure

Snellen chart

Lettered chart for measuring visual acuity; usually tested at 20 feet (hence, 20/20 vision)




Eye misalignment caused by extraocular muscle imbalance


Acute pustular infection of oil glands located in an eyelash follicle



Rapid decrease in response to a given dose of a drug after repetitive administration

Tarsal gland

Oil gland within the eyelid tissue; secretes the outer portion of the tear film to prevent tear evaporation and overflow

Tear breakup time

Tests the time between a blink and the development of a dry spot on the ocular surface; less than 10 seconds is abnormal

Tear duct

Tear drainage channel from the lacrimal sac to the mucous membrane of the nose


Fluid secreted by the lacrimal glands to keep the conjunctiva and cornea moist

Temporal pallor

Loss of pinkish tone in the optic disc; usually indicates optic nerve damage


Three times daily


Instrument that measures intraocular pressure; each type of tonometer measures pressure through slightly different means

Toric lens

An optical device with a cylindrical component to correct astigmatism

Trabecular meshwork

Structure inside the eye at the iris-scleral junction of the anterior chamber angle that filters aqueous fluid and controls its exit from the eye through Schlemm’s canal


Surgical procedure to remove part of the trabecular meshwork to increase the outflow of aqueous fluid to treat elevated intraocular pressure


Surgical procedure that uses a laser to burn part of the trabecular meshwork to increase outflow of aqueous fluid to treat elevated intraocular pressure


Severe, chronic, and contagious infection of the eyelid and cornea caused by a virus; the leading cause of blindness in the world


Optical device that incorporates lenses of 3 different powers


Ocular defect that causes images to appear in triplicate; often caused by an early cataract


Ultraviolet light

Light with wavelengths between 250 and 400 nanometers; invisible to the naked eye


Pigmented vascular layers of the eye (iris, ciliary body, and choroid) that contain most of the eye’s blood vessels


Inflammation of any of the structures of the uvea (iris, ciliary body, or choroid)



Ability of the eye to receive and transmit light images to the brain, where they are interpreted; the ability to see

Visual acuity

Measurement that assesses the eye’s ability to distinguish details and shapes

Visual field

The full area visible to the eye when fixated straight ahead; measured in degrees


Surgical removal of the vitreous


Transparent gelatinous mass that fills the back two-thirds of the eyeball between the lens and retina


Year-round allergies

Also known as perennial allergies, these are likely due to indoor allergens such as pet dander