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Glossary of Terms

Here is a glossary of common terms used in the field of optometry.

Ablation Refers to the surgical removal of eye tissue to correct a refractive error such as myopia (near sightedness). In laser procedures such as LASIK, the excimer laser ablates, or removes, tissue from the cornea.

accommodation disorder Accommodation refers to the eye's ability to automatically change focus from seeing at a distance to seeing at near. Accommodation disorders are marked with symptoms that may include blurred vision, double vision, eyestrain, headache, fatigue and difficulty oncentrating (particularly while reading).

acrodermatitis enteropathica Rare inherited condition characterized by dermatitis, hair loss, diarrhea and zinc deficiency. Eye symptoms commonly include light sensitivity, but conjunctivitis and other symptoms may also be present.

AK (astigmatic keratotomy) A surgical procedure to reduce astigmatism. The surgeon cuts the cornea so that it is more spherical when it heals.

allergy Reaction of the body's immune system to a foreign substance (e.g., pollen, animal dander, etc.). When the eyes are affected, the most common symptoms are redness, itching, chemosis, tearing, swollen eyelids and stickiness.

amaurosis fugax Sudden and usually temporary vision loss caused when a clot or blockage disrupts blood flow to the eye (eye stroke). Symptoms can include curtain-like darkness, usually in just one eye.

amblyopia Also called lazy eye, is caused by undeveloped central vision in one eye that leads to the use of the other eye as the dominant eye. The leading cause is Strabismus, followed by anisometropia. There are no symptoms, but the patient may be found squinting and closing one eye to see.

AMD or ARMD (age-related macular degeneration) Disorder characterized by the gradual loss of central vision due to a damaged macula (which is made up of retinal cones necessary for sight).

angiogenesis The formation of new blood vessels in the body.

angle (in glaucoma) Refers to the drainage channel for the aqueous humor in the eye; improper drainage can lead to the high intraocular pressure associated with glaucoma. In narrow-angle glaucoma, the channel is blocked, whereas open-angle glaucoma has other causes, such as the body producing too much aqueous humor.

aniridia Absent or partially absent iris, typically congenital. Additional symptoms include poor vision and photophobia.

anisocoria Unequal pupil size. Causes include glaucoma, head or eye trauma, an intracranial tumor, infection of the membranes surrounding the brain and previous intraocular surgery. A small percent of the population has unequal-sized pupils naturally, without any known cause.

anisometropia Condition where the eyes have a significantly different refractive power from each other, requiring a different prescription for each eye.

anophthalmos Absence of one or both eyes. Anophthalmos may be congenital or due to trauma, infection or other causes, with symptoms including reduced depth perception and peripheral vision.

ANSI The American National Standards Institute is a private, non-profit organization that coordinates efforts to develop standards for manufacturing many different products, including eyeglass lenses, including acceptable levels of impact resistance for safety eyewear.

ANSI Z87.1-2003 Standard 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.

anterior chamber Part of the eye behind the cornea and in front of the iris and lens.

antibody A protein activated by the body's immune system that fights infection, toxins and other foreign substances.

antioxidant Substance that inhibits oxidation and can guard the body from damaging effects of free radicals. Antioxidant vitamins include B, C and beta carotene. Antioxidants may help prevent macular degeneration and other other eye diseases.

anti-reflective coating (AR coating) Thin layer(s) applied to a lens to reduce the amount of reflected light and glare that reaches the eye.

aqueous humor Clear fluid in the front of the eye, between the cornea and the iris, that provides nutrients to the cornea and the lens. Glaucoma causes difficulty in draining this fluid, and pressure builds, resulting in damage to the optic nerve and loss of vision.

arcus An opaque arc or ring around the peripheral cornea, this represents fatty or oily deposits in the cornea.

Argyll Robertson pupil Small, irregular pupil, usually caused by syphilis. Argyll Robertson pupils do not respond to light.

asteroid hyalosis A benign condition that creates suspended particles within the eye's interior, observable by an eye doctor during an exam.

astigmatism Condition in which the cornea's curvature is asymmetrical (the eye is shaped like a football or egg instead of a baseball); light rays are focused at two points on the retina rather than one, resulting in blurred vision.

atopy Type of allergy where levels of the antibody immunoglobin E are increased; atopy includes rhinitis, asthma, hay fever and eczema.

best corrected visual acuity (BCVA) The best vision you can achieve with correction.

bifocal Lens that includes correction for both near vision and far vision.

binocular vision Ability of both eyes to work together to achieve proper focus, depth perception and range of vision.

blepharitis Inflammation of the eyelid(s), typically around the eyelashes, caused by various types of dermatitis, rosacea and allergic reactions. Symptoms include a red or pink eyelid, crusty lid or lashes, burning, foreign body sensation, eye or eyelid pain or discomfort, dry eyelid, dry eye, eyelash loss, grittiness, stickiness, eyelid swelling and tearing.

blepharochalasis Excessive, drooping eyelid skin caused by recurring swelling.

blepharoconjunctivitis Inflammation of the eyelid and conjunctiva, caused by infections and allergic reactions. Symptoms include a red or pink eye, a red or pink eyelid, pain or discomfort of the eye or around the eye, tearing, burning, eye dryness and eye stickiness.

blepharospasm Involuntary increased blinking that progresses to spasms in both eyes. The exact cause is unknown, but doctors believe it to be a central nervous system disorder. It can produce a functional blindness since the patient can't open his or her eyes long enough to function visually.

Bowman's membrane Corneal layer between the epithelium and the stroma.

bridge The part of eyeglasses that extends across the nose.

canaliculitis Inflammation of a tear duct (or ducts), caused by a bacterial infection. Symptoms include discharge, a red or pink eye and a swollen upper or lower eyelid near the nose.

cataract Clouding of the natural lens of the eye, usually caused by aging in conjunction with other risk factors, such as exposure to the sun's UV rays, smoking, steroid intake and diabetes. Symptoms include blurred vision, glare, halos around lights, colors that are less bright, a cloudy spot in your vision and, sometimes, temporary vision improvement. 

cellulitis Inflammation of tissue around the eye.

central serous retinopathy Disorder in which fluid collects under the central retina (macular area) and disrupts central vision. The cause is unknown. Symptoms include blurred central vision and metamorphopsia.

cerebral cortex Outer portion of the brain where complex functions including certain vision processes take place.

chalazion A small bump on the eyelid caused by an obstructed meibomian gland. Additional symptoms include light sensitivity, tearing and eyelid swelling.

chemosis Conjunctival swelling that is often caused by an allergy.

choroidal neovascularization Abnormal growth of new blood vessels in the choroid, commonly associated with macular degeneration. Symptoms include vision loss and metamorphopsia.

CK (Conductive Keratoplasty) Surgical procedure using radio waves to heat collagen in the cornea's periphery to shrink it and reduce hyperopia (farsightedness), and treat presbyopia.

CMV retinitis (cytomegalovirus retinitis) Serious eye infection usually found in those with immune problems, such as AIDS patients; symptoms include floaters, blind spots, blurry vision and vision loss.

color blindness Partial or total inability to distinguish specific colors. Color blindness is inherited, and is much more common in men than in women.

computer vision syndrome Collection of problems, mostly eye- and vision-related, associated with computer use. Symptoms include eyestrain, dry eyes, blurred vision, red or pink eyes, burning, light sensitivity, headaches and pain in the shoulders, neck and back.

cone A photosensitive receptor in the retina that helps you to see color.

conjunctivitis Inflammation of the conjunctiva, characterized by a pink eye. The cause is either infectious or allergic. "Pink eye" is commonly used to describe types of conjunctivitis. Other symptoms include burning, discharge, dryness, itching, light sensitivity, pain or discomfort, stickiness, tearing and chemosis.

contact lens drops Eyedrops for contact lens wearers; regular eyedrops can discolor contact lenses.

contact lens problem Contact lens problems can range from minor to sight-threatening, and include protein build-up, debris on the lens, a ripped or nicked lens, infections and more. Symptoms can include frequent blinking, blurred vision, burning, discharge, foreign body sensation, itching, light sensitivity, eye pain or discomfort, a red or pink eye or lid and eyelid swelling.

convergence Eyes' ability to turn inward. People with convergence insufficiency have trouble (eyestrain, blurred vision, etc.) with near tasks such as reading.

cornea The clear part of the eye covering the iris and pupil; it lets light into the eye, permitting sight.

corneal abrasion A loss of the epithelial layer of the cornea, typically due to minor trauma (contact lens trauma, a sports injury, dirt or another foreign body, etc.). Symptoms include blurred vision, foreign body sensation, grittiness, light sensitivity, eye pain or discomfort, a red or pink eye and tearing.

corneal dystrophy One of a group of conditions, usually hereditary, in which the cornea loses its transparency. Symptoms include blurred vision, foreign body sensation, light sensitivity, eye pain or discomfort and vision loss.

corneal edema Swelling of the eye's cornea; causes include intraocular surgery, corneal dystrophies, high intraocular pressure and contact lens complications. Symptoms include vision loss, halos around lights, a white or cloudy spot on the eye, photophobia, eye pain and foreign body sensation.

corneal erosion Recurrent breakdown of the corneal epithelium. Symptoms include blurred vision, foreign body sensation and eye pain or discomfort.

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

corneal opacity A cloudy spot in the cornea, which is normally transparent. Causes include corneal scar tissue and infection. Symptoms include halos around lights, photophobia, vision loss and a white or cloudy spot on the eye.

corneal ring Type of vision correction surgery where a doctor inserts a tiny plastic ring into the cornea (which lets light into the eye). This ring reshapes the cornea, helping it to focus light better onto the retina, resulting in clearer vision. The ring can be adjusted and even removed if desired.

corneal topography Light shined onto the surface of the eye to measure the reflected light to create a map of the cornea's curvature as well as any irregularities. The map is used for evaluations related to refractive surgery, contact lens fitting and corneal disease management. It is especially useful for measuring astigmatism.

corneal ulcer An ocular emergency involving an infected corneal abrasion. Frequently found in extended wear contact lens wearers. Symptoms include light sensitivity, eye pain or discomfort, a red or pink eye, a white or cloudy spot on the eye and tearing.

crossed eyes Type of strabismus (a misalignment of the eyes) where one or both eyes point inward, toward the nose.

cystoid macular edema (CME) Swelling of the eye's macula, caused by an excessive amount of fluid.

dacryoadenitis Inflammation of the tear gland, typically caused by a viral or bacterial infection. Symptoms include a dry eye, a red or pink eyelid, swelling of the lid or around the eyes and ptosis.

dacryocystitis Inflammation of the nasolacrimal (tear) sac. Symptoms include discharge, a sticky eye, eye pain or discomfort, a red or pink eye, swelling around the eye and tearing.

dacryostenosis Blocked tear duct characterized by excessive tearing, discharge or sticky eye.

daily wear These soft contact lenses are worn every day for six months up to a couple of years. They require daily cleaning and disinfecting, as well as a periodic enzymatic soak (usually once a week).

decentered ablation Refractive surgery complication in which the laser is not centered on the pupil when it removes tissue. Symptoms include glare, double vision and halos.

diabetic maculopathy Eye disease related to diabetes that creates swelling and abnormal leakage of fluids and fats into the macula, where fine focusing and central vision occur. Severe diabetic maculopathy can cause loss of central vision and blindness.

diabetic retinopathy Leaking of retinal blood vessels in advanced or long-term diabetes, affecting the macula or retina.

diabetic vitreous hemorrhage Bleeding into the gel-like (vitreous humor) interior of the eye, originating from blood vessels weakened by diabetes.

diopter Unit of measure for the refractive (light-bending) power of a lens; eye care practitioners use it in eyeglass and when prescribing contact lenses.

diplopia Also called double vision.

disposable contact lenses Technically, this is any contact lens that is thrown away after a short period of time. Among most eye care practitioners, "disposable" usage ranges from one day to two weeks, while "frequent replacement" lenses are discarded monthly or quarterly.

double vision (diplopia) When two images of the same object are perceived by one or both eyes.

drooping eyelids (ptosis) Condition in which only the upper eyelid(s) only sag.

dry eye Lack of sufficient lubrication and moisture in the eye. Most dry eye complaints are temporary and easily relieved.

dry eye syndrome Chronic dryness due to reduced quality or quantity of the eye's tear film, or due to increased evaporation of the existing tear film. Dry eye syndrome has many causes, including aging, certain systemic diseases and long-term contact lens wear. Additional symptoms include foreign body sensation, eye pain or discomfort, burning, grittiness, itching, light sensitivity, frequent blinking, a red or pink eye and tearing.

ectropion An abnormal turning out of an eyelid, typically the lower one, which exposes the inner, conjunctival side of the eyelid; usually due to aging. Additional symptoms include eye or lid pain or discomfort, a red or pink eye or eyelid and overflow tearing.

edema Accumulation of an excessive amount of watery fluid, which causes swelling.

endophthalmitis An ocular emergency involving inflammation of the interior of the eye, typically caused by an infection from eye surgery or trauma. Symptoms include floaters, light sensitivity, eye pain or discomfort, a red or pink eye and vision loss.

enophthalmos The sinking of the eye into the socket. Causes include development problems in utero, trauma and inflammation.

entropion An abnormal turning in of an eyelid, which causes the lashes to rub on the ocular surface; usually due to aging. Additional symptoms include eye or lid pain or discomfort, foreign body sensation, a red or pink eye, itching, tearing and vision loss.

enzymatic cleaner A cleaner that removes protein deposits and other debris from contact lenses. 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.

epiretinal membrane Thin layer of scar tissue on the retina.

epithelial ingrowth LASIK complication in which epithelial cells grow under the LASIK flap; epithelial ingrowth does not usually affect vision.

epithelium The cornea's outer layer of cells.

esotropia When one or both eyes point inward, so the eyes are "crossed."

excimer laser An instrument that uses shorter wave (ultraviolet) light to vaporize and remove tissue from the eye's surface during vision correction procedures.

exotropia When one or both eyes point outward; also called "walleyed."

extended wear Currently, these contact lenses are FDA-approved to be worn without removal for up to seven days (or 30 days in the case of one brand), meaning some people will be comfortable sleeping with them in their eyes. Thirty-day contact lenses are sometimes referred to as "continuous wear."

eye care practitioner Optometrists (ODs) and ophthalmologists (MDs) both practice eye care, but in different, though often overlapping, areas: In the United States, ODs (Doctors of Optometry) examine eyes for both vision and health problems, prescribe eyeglasses, prescribe and fit contact lenses, and treat some eye conditions and diseases. ODs attend four years of optometry school after attaining their BS or BA college degree. MDs are medical doctors who specialize in the eyes. They examine eyes, treat disease, perform surgery, and prescribe glasses and contacts. Like other physicians, they complete a BS or BA degree, attend four years of medical school, and complete a residency program in their practice specialty. Both ODs and MDs often pursue further subspecialty fellowship training, and they take additional continuing education courses during their careers in order to stay up to date and to maintain state and national board certifications. Other non-doctor eye care practitioners include paraoptometrics, contact lens technicians, and opticians, whose training and continuing education requirements can differ depending on the state in which they practice.

farsightedness Also called hyperopia. To farsighted people, near objects are blurry, but far objects are in focus.

femtosecond laser Device that creates bursts of laser energy at an extremely fast rate measured in terms of a unit known as a femtosecond (one quadrillionth of a second). These ultra fast energy pulses precisely floaters A dark or gray spot or speck that passes across your field of vision and moves as you move your eye. As your eye ages, the gelatinous vitreous humor begins to liquefy in the center of the gel. Floaters are caused by the undissolved vitreous humor that floats in the liquid vitreous. Sometimes, a "shower of floaters" is a sign of a serious condition, particularly if you also see flashes of light.

fluorescein angiography An imaging test that involves first injecting fluorescent yellow-green dye into the veins. When the dye reaches interior regions of the eye, it provides opportunity for high contrast photography or other imaging of blood vessels. Fluorescein angiography particularly is useful in diagnosing age-related macular degeneration.

foreign body Something in or on the eye that doesn't belong there. Symptoms include foreign body sensation, eye pain or discomfort, a red or pink eye, tearing, frequent blinking, blurred vision, discharge, light sensitivity and vision loss.

foreign body sensation Sensation that something is in your eye.

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

frequent replacement contact lenses Also called planned replacement. Technically, this is any contact lens that is thrown away after a moderately short period of time. Among most eye care practitioners, "disposable" usage ranges from one day to two weeks, while "frequent replacement" lenses are discarded monthly or quarterly.

fungal keratitis eye infection The source of a 2006 outbreak of fungal eye infections among contact lens wearers is a fungus known as Fusarium, found in places such as soil, water, and organic matter including plants. Symptoms can be severe, and if untreated, the infection may become so eye-damaging that a corneal transplant is required.

glaucoma Disease characterized by elevated intraocular pressure, which causes optic nerve damage and subsequent peripheral vision loss. Most people have no initial symptoms of chronic (open-angle) glaucoma, but you can develop peripheral vision loss, headaches, blurred vision, difficulty adapting to darkness and halos around lights. Other forms of glaucoma (e.g., closed-angle glaucoma) may have additional symptoms such as eye pain, a pupil that doesn't respond to light, redness, nausea and a bulging eye.

glycemic index A method of ranking foods in terms of how quickly they affect blood sugar levels. For example, foods with high glycemic index rankings (processed foods such as white flour, sugar, etc.) can cause unhealthy spikes in blood sugar. Foods with lower glycemic index rankings, such as whole grains, create more stable blood sugar levels.

Graves' ophthalmology Autoimmune eye disorder usually associated with abnormalities of the thyroid gland; symptoms include eyelid retraction, bulging eyes, light sensitivity, eye discomfort, double vision, vision loss, a red or pink eye and a limited ability to move the eyes.

hard contact lenses Rarely worn now, these are the small, hard lenses made of PMMA material that many people wore in the '70s and '80s. Compared with modern soft and rigid lenses, they are less healthy to wear long-term, since the material doesn't allow oxygen to reach the surface of the eye.

hemifacial spasm Involuntary muscles twitches on one side of the face, typically caused by compression of the seventh (facial) cranial nerve by a neighboring blood vessel somewhere in the brain.

higher-order aberration Irregularity of the eye other than a refractive error (myopia, hyperopia or astigmatism). Higher-order aberrations sometimes affect your vision (such as decreasing contrast sensitivity), and sometimes do not.

Horner's syndrome Condition characterized by a small pupil, ptosis and an abnormal lack of facial perspiration (all on the same side of the face); Horner's syndrome is caused by injury to the sympathetic nerves of the face.

hyperopia Also called farsightedness, hyperopia is a condition in which the length of the eye is too short, causing light rays to focus behind the retina rather than on it, resulting in blurred near vision. Additional symptoms include eyestrain and squinting.

hypotony Low intraocular pressure, often caused by eye surgery or trauma (e.g., open globe injury). Symptoms include blurred vision and eye pain or discomfort.

intraocular lens (IOL) Artificial lens that a cataract surgeon places in a patient's eye after removing the eye's natural lens. Like a contact lens, it has a built-in refractive power tailored specifically to the patient's visual condition.

intraocular pressure (IOP) Eye pressure, as determined by the amount of aqueous humor filling it. High IOP (ocular hypertension) can be a sign of glaucoma.

iris A pigmented membrane that lies between the cornea and the lens; it acts as a diaphragm to widen or narrow the opening called the pupil, thereby controlling the amount of light that enters the eye.

iritis Inflammation of the iris.

jaundice Yellow coloring in the skin and eyes caused by high levels of a pigment called bilirubin. Jaundice is associated with a variety of conditions involving the liver, gallbladder and bile ducts, including hepatitis and cirrhosis.

keratectomy Surgical removal of part of the cornea.

keratitis Inflammation of the cornea, caused by an infection or inflammatory process. Symptoms include eye pain or discomfort, light sensitivity, foreign body sensation, grittiness and tearing.

keratoconjunctivitis Inflammation of the cornea and conjunctiva.

keratoconjunctivitis sicca (dry eye syndrome) Lack of sufficient lubrication and moisture in the eye.

keratoconus Degeneration and thinning of the cornea resulting in a cone-shaped bulge (a type of irregular astigmatism). The cause is unknown, but may be genetic.

keratoplasty Any of several types of corneal surgery, such as shrinking the collagen to reduce farsightedness or transplanting a new cornea.

keratotomy Incision of the cornea.

keratometer An instrument that measures the curvature of the eye's clear, front surface (cornea).

laser photocoagulation Procedure in which a surgeon uses a laser to coagulate tissue, usually to seal leaking blood vessels and destroy new ones in diseases like macular degeneration and diabetic retinopathy.

LASIK (Laser-Assisted In Situ Keratomileusis) Surgical procedure in which a tiny flap is cut in the top of the cornea, underlying corneal tissue is removed with an excimer laser, and the flap is put back in place.  LASIK corrects myopia, hyperopia, astigmatism, and presbyopia.

Leber's congenital amaurosis Inherited condition characterized by vision loss or blindness at birth or shortly thereafter. The exact cause is unknown, but doctors believe that the retina may degenerate, or that its photoreceptors may not develop properly.

lens 1. The nearly spherical body in the eye, located behind the cornea, that focuses light rays onto the retina. 2. A device used to focus light into the eye in order to magnify or minify images, or otherwise correct visual problems. Eyeglass lenses, contact lenses, and intraocular lenses are examples.

lens dislocation Full or partial displacement of the eye's lens. Dislocation is often caused by trauma to the eye or head, but may also be inherited or come as the result of certain systemic conditions, such as Marfan's syndrome or homocystinuria.

lipid Organic compound that is oily, fatty, or waxy and commonly found in living cells. Lipids are one component of human tears, forming an oily outer layer that helps keep the eye moisturized by reducing evaporation of the watery and mucus layers beneath it. Lipids can collect on contact lenses, making them uncomfortable.

low vision (partial sight) Usually results from an eye disease such as glaucoma or macular degeneration.  Sight that cannot be satisfactorily corrected with glasses, contacts, or surgery.

LTK (Laser Thermal Keratoplasty) Also called Laser Thermokeratoplasty. Surgery to correct mild farsightedness in people over 40; the doctor uses a holmium laser to heat the cornea and shrink its collagen.

lupus erythematosus Inflammatory skin disorder. The exact cause is unknown, but some people appear to have a genetic predisposition to developing lupus, and it is much more common in women than men. Systemic symptoms vary depending on the type of lupus, but red patches on the cheeks are common. When lupus affects the eyes, it can have such symptoms as a red or pink lid, a spot or scale on the lid that may change in pigment (generally losing pigment except for darker color marking the border of the spot), eyelash loss, dry eye syndrome, migraine headaches, uveitis, scleritis, conjunctivities, and retinal vascular occlusion (blockage in the retina's vascular system).

macula Part of the eye near the middle of the retina; the macula allows us to see objects with great detail.

macular degeneration Disorder characterized by changes in the eye's macula that result in the gradual loss of central vision. Central vision may be blurred, distorted (metamorphopsia) or shadowy before vision loss occurs.

macular edema Swelling of the central portion of the retina (macula), due to buildup of fluid leaking from retinal blood vessels. Causes temporary or permanent vision loss if untreated.

madarosis Eyelash or eyebrow loss. Causes include infections, metabolic disorders, blepharitis, certain drugs, lupus erythematosus and trauma.

meibomian gland Gland found in the eyelid that produces the oily outer layer of the three-layer tear film that lubricates the eye.

meibomianitis Inflammation of the meibomian glands; rosacea is a common cause. Symptoms include red or pink eyelid margins, a red or pink eye, dryness, burning, blurred vision and a swollen eye.

meningitis Inflammation of the meninges, membranes that envelope the brain and spinal cord. Viruses and bacteria can cause meningitis. Symptoms include fever, headache, vomiting, a stiff neck and light sensitivity.

metamorphopsia Vision problem in which objects appear distorted, typically caused by conditions or diseases that affect the eye's macula and retina. Straight lines may appear to be wavy, curved or bent, objects may appear to be larger or smaller than they actually are, or closer or farther away than they actually are.

microcornea Abnormally small cornea.

microphthalmia Congenital defect resulting in an abnormally small eye or eyes. The cause is usually unknown. Microphthalmia typically results in blindness or reduced vision, but normal vision is possible if the eyes are nearly normal in size.

migraine Severe headache, sometimes accompanied by nausea and visual disturbances. Eye and vision symptoms include blurred vision, ptosis, halos around lights, light flashes, light sensitivity, eye pain or discomfort, vision loss (blind spots in central vision, tunnel vision or overall impaired vision), distorted vision and wavy lines in vision.

monochromatic Refers to one wavelength of light, as opposed to the many wavelengths of light found in varying colors.

monofocal Type of spectacle lens, intraocular lense (IOL) or contact lens design that has only one area through which the eye focuses. A multifocal lens has more than one focal area, enabling sight at multiple distances, typically for people with presbyopia.

monovision Vision correction method for those with presbyopia in which one eye is corrected for near vision and the other for far, either through contact lenses or refractive surgery. Monovision eliminates the need for reading glasses, but does have some drawbacks, including decreased depth perception.

multifocal Type of spectacle lens, intraocular lens (IOL) or contact lens design that includes more than one area through which the eye focuses. Examples are bifocals or trifocals. This enables sight at multiple distances, typically for people with presbyopia.

myasthenia gravis Weakness of the voluntary muscles, believed to be autoimmune in nature. Symptoms include double vision and eyelid ptosis; patients sometimes have non-eye symptoms as well, such as difficulty swallowing or using the arms and legs.

myokymia Common eyelid twitch typically brought on by stress or fatigue.

myopia Also called nearsightedness. Condition in which the length of the eye is too long, causing light rays to focus in front of the retina rather than on it, resulting in blurred distance vision. Additional symptoms include eyestrain, poor night vision and squinting.

nearsightedness (myopia) Condition in which visual images come to a focus in front of the retina, resulting in defective vision of distant objects.

neovascularization Abnormal growth of new blood vessels, such as in an excessive amount, or in tissue that normally does not contain them, or of a different kind than is usual in that tissue.

neuroretinitis Inflammation of the optic nerve and retina, commonly caused by an infection. Symptoms include blurred vision, headache, floaters, eye pain or discomfort, vision loss and loss of color vision.

nose pad One of a pair of pads, usually clear, that rest on either side of your nose and help to support your glasses.

nystagmus Rapid and involuntary eye movement that is oscillating and non-chaotic. Blurred vision may result. Nystagmus typically affects infants and has a variety of causes.

ocular herpes Recurrent viral infection that can cause inflammation and scarring of the cornea. It is not sexually transmitted.

ocular hypertension Condition in which the intraocular pressure of the eye is elevated above normal and which may lead to glaucoma.

ocular migraine Visual phenomena that may accompany a migraine headache or that may occur without any headache. They include light flashes, spots, wavy lines, flickers, zig-zagging lights, semi-circular or crescent-shaped visual defects and distortions of shapes.

ophthalmologist A medical doctor (MD) who specializes in the eye. Ophthalmologists perform eye exams, treat disease, prescribe medication, and perform surgery. They may also write prescriptions for eyeglasses and contact lenses.

ophthalmoplegia Eye muscle paralysis. Causes include stroke, multiple sclerosis, a tumor, thyroid disease, migraines and progressive supranuclear palsies. Symptoms can include limited eye movement, blurred vision, double vision, nystagmus and ptosis.

optical coherence tomography A method of imaging that, in ophthalmology, uses light waves to provide cross-sectional views of interior eye structures. Also known as OCT.

optician In the United States, opticians are not doctors, but in some states they must complete training and be licensed. And in some states they can, after special training, become certified to fit contact lenses. Most opticians sell and fit eyeglasses, and specialty eyewear that are made to an optometrist's or ophthalmologist's prescription. Many also have equipment on the premises so they can grind lenses and put them in frames without ordering from a lab.

optic nerve The nerve that carries electrical impulses from photoreceptor cells (rods and cones) in the retina to the visual cortex in the brain.

optic nerve head Also called optic disk. Circular area where the optic nerve enters the retina, and the location of the eye's blind spot.

optic nerve problem The optic nerve (second cranial nerve) is the part of the eye that carries stimuli from the rods and cones to the brain. Problems such as inflammation (optic neuritis), tumors and swelling can lead to symptoms such as: blurred vision, loss of color vision, floaters, headache, eye pain or discomfort, nausea and vision loss.

optometrist Doctors of optometry (ODs) examine eyes for both vision and health problems, prescribe glasses, and fit contact lenses. They can prescribe many ophthalmic medications and may participate in your pre- and postoperative care if you have eye surgery. ODs must complete four years of post-graduate optometry school for their doctorate.

orbital pseudotumor An inflammatory mass in the tissues around or behind the eye that looks like and mimics the symptoms of a tumor. The cause is unknown. The primary symptom is a painful, bulging eye. You may also experience pain or discomfort around the eye.

orthokeratology (ortho-k) Procedure in which a doctor fits you with special gas permeable contact lenses to reshape your cornea and correct errors like nearsightedness. Often, patients wear the lenses just at night.

OS Abbreviation for "oculus sinister," the Latin term for "left eye."

osteopetrosis Rare, hereditary disease in which the bones are too dense. Common symptoms include bone pain and fractures. Retinal degeneration may occur; it results in vision loss.

papilla Small bump where the optic nerve exits the eye.

papilledema Swelling with accompanying compression of the optic nerve head, which can be a medical emergency. Causes of papilledema can include bleeding near the vicinity of the optic nerve and abnormally high cerebrospinal fluid (CSF) pressure. Autoimmune disorders, trauma and infections of the central nervous system also can cause papilledema.

Parinaud dorsal midbrain syndrome Inability to look up, typically associated with a brain lesion, characterized by nystagmus and pupil unresponsiveness to light. Causes include hydrocephalus ("water on the brain") and tumors of the pineal gland.

Parkinson's disease Neurological disorder characterized by tremors, muscle rigidity, a shuffling walk and a mask-like appearance in the face. Parkinson's may also cause infrequent blinking.

Patau syndrome Also called Trisomy-13. Condition caused by an extra, third copy of chromosome 13. Symptoms include severe mental retardation, a small head, microphthalmia, a cleft lip or palate, heart defects and extra fingers or toes; many patients also have an iris coloboma and retinal dysplasia (abnormal development). The majority of infants with Patau syndrome die within the first year.

peripheral vision The edges of your visual field.

phacoemulsification Also called "phako," this in-office cataract surgery procedure involves using a device with a vibrating, ultrasonic tip to break up the cataract, then suctioning the pieces out with a tiny needle.

phoropter Device that provides various combinations of lenses used for tests of vision errors in eye examinations.

photoablation Procedure in which a surgeon uses ultraviolet radiation to remove tissue.

photocoagulation Use of heat from a high-energy laser to seal off bleeding in damaged tissue.

photokeratitis "Sunburn" of the cornea; symptoms include discomfort, blurred vision, and light sensitivity. The temporary vision loss that can result is called "snow blindness."

photophobia Discomfort from sun or other light.

photopsia Flashes of light often noticed in the edges of the visual field. Photopsia can have many causes, including mechanical (rather than visual) stimulation of light-sensitive cells (photoreceptors) in the retina. photoreceptor A light-sensitive cell found in the retina. Photoreceptors in the human retina are classified as cones and rods. Cones are located in the central retina (the fovea) and control color vision. Rods are located outside the fovea and control black/white vision in low-light conditions.

phytochemicals Chemicals found in plants that help protect against disease.

pinguecula A yellowish, thickened lesion on the conjunctiva near the cornea. Pingueculae represent a benign degenerative change in the conjunctiva caused by the leakage and deposition of certain blood proteins through the permeable capillaries near the limbus.

plano A term eye care professionals use to describe lenses with no corrective power. The term is most often applied to nonprescription sunglasses or contact lenses that are worn for cosmetic purposes only.

polarized lenses Lenses that block light reflected from horizontal surfaces such as water, to reduce glare.

posterior chamber Part of the eye behind the iris and in front of the lens.

presbyope Person who has difficulty reading print and seeing near objects.

presbyopia Condition in which the aging eye beginning at around age 40 is unable to focus at all distances, often noticed when print begins to blur.

prism In optics, a lens that can have precise geometric configurations enabling light to be bent or reflected in certain ways. A prism also can split white light into different wavelengths and colors.

PRK (Photorefractive Keratectomy) Surgical procedure in which an excimer laser is used to remove corneal tissue to correct vision problems.

progressive lenses Also called progressive addition lenses or PALs. Multifocal lenses whose corrective powers change progressively throughout the lens. A wearer looks through one portion of the lens for distance vision, another for intermediate vision, and a third portion for reading or close work. Each area is blended invisibly into the next, without the lines that traditional bifocals or trifocals have.

proliferative vitreoretinopathy (PVR) A common complication of surgery for retinal detachment, which causes scarring of the retina.

pseudotumor cerebri A condition whose symptoms mirror those of a brain tumor: increased intracranial pressure, headache, nausea, brief periods of vision loss (graying or blurring) and double vision. The cause is unknown, but patients are often obese women.

pterygium Triangular fold of tissue on the white of the eye that can eventually grow over part of the cornea; the cause may be irritation from sun (i.e., UV rays), dust and wind.

ptosis Drooping eyelid. Congenital ptosis is caused by a problem with the levator muscle (which lifts the eyelid). In adults, ptosis is commonly caused by the aging of the levator's connective tissue.

punctal plugs Tiny inserts often made of plastic that are placed in channels or ducts of the eye where moisture drainage occurs. Punctal plugs can help stop excessive drainage to keep the eye moistened in conditions such as dry eye syndrome.

pupil The round, dark center of the eye, which opens and closes to regulate the amount of light the retina receives.

pupillary distance This is the distance between the center of each pupil. Opticians use a special ruler to measure your pupillary distance before ordering your eyeglasses. It is an essential measurement because the optical center of each eyeglass lens must be positioned directly over the center of each pupil. An incorrect measurement means you would have difficulty focusing when wearing the glasses.

reading glasses Also called readers. Glasses to help with close work, particularly for people who are presbyopic.

refractive error When light rays don't properly refract from the cornea to the retina, it is a refractive error. This can take the form of myopia (nearsightedness), hyperopia (farsightedness) or astigmatism.

refractive surgery corrects visual acuity, with the objective of reducing or eliminating the need for glasses and contacts. Includes radial keratotomy, PRK, LASIK, and corneal implants.

retina The sensory membrane that lines the eye; it is composed of several layers and functions as the immediate instrument of vision by receiving images formed by the lens and converting them into signals which reach the brain by way of the optic nerve.

retinal detachment Condition where the retina separates from the choroid. Retinal detachments have many causes, including aging, surgery, trauma, inflammation, high myopia and diseases such as diabetic retinopathy, retinopathy of prematurity and scleritis. Symptoms include light flashes, floaters, a shadow coming down over yourvision, blurred vision and vision loss.

retinal tear A tear or split in the retina typically caused by a vitreous detachment. Symptoms include floaters and light flashes.

retinitis Inflammation of the retina. Symptoms include blurred vision, metamorphopsia, floaters and vision loss.

retinitis pigmentosa Usually inherited condition characterized by progressive degeneration of the retina, resulting in night blindness and decreased peripheral vision.

retinoschisis Condition in which the retina splits into layers, sometimes causing blurred vision. It is either inherited or acquired; the acquired form is caused by small cysts in the eye.

RGP (Rigid Gas Permeable) Type of contact lens made of breathable plastic that is custom-fit to the shape of the cornea. RGPs are the successor to old-fashioned hard lenses, which are now virtually obsolete.

rheopheresis The RHEO Procedure ("rheopheresis") is a method of blood filtration for treatment of dry age-related macular degeneration that removes large proteins and fatty components from the blood to improve circulation to macular cells at the back of the eye.

rheumatoid arthritis Chronic, autoimmune, inflammatory disorder that mainly affects the joints. Symptoms include pain, stiffness, swelling and deformities. Rheumatoid arthritis may also cause eye burning, discharge and dryness.

RK (Radial Keratotomy) Surgical procedure where cuts are made in the cornea in a radial pattern, to flatten the cornea and correct myopia. However, RK now is virtually obsolete as a corrective eye procedure.

rod A photosensitive receptor in the retina that helps you to see in low light.

sclera The outer coat of the eyeball that forms the visible white of the eye and surrounds the optic nerve at the back of the eyeball.

scleritis Inflammation of the sclera. Autoimmune disorders are the most common cause. Symptoms include a red or pink eye, eye pain, light sensitivity, tearing and blurred vision.

scotoma Blind spot within the field of view.

seborrheic dermatitis Skin condition that causes scales, redness and itching; it commonly affects the scalp (dandruff), eyebrows, eyelids, nose, area behind the ears and sternum. It is associated with seborrheic blepharitis.

segment A part, as in the near-vision portion of a pair of bifocals.

silicone Type of flexible and comfortable plastic. Because it is commonly used in nose pads in eyeglasses, people who are allergic to silicone should ask their eye doctor for a different type of nose pad.

single vision A lens that has the same power throughout the entire lens, in contrast to a bifocal or multifocal lens that has more than one lens power.

sinusitis Inflammation of the sinuses, due to an infection or an allergic reaction. Probably the most common cause of pain in and around the eye. Symptoms include head pain (headache, pain around the eyes, toothache, jaw pain), nasal discharge, postnasal drip, coughing, eyelid swelling, swelling around the eyes, a stuffy nose, fatigue, bad breath and a sore throat.

Sjogren's syndrome An inflammatory autoimmune disorder characterized by a dry mouth and dry eyes. Additional eye symptoms include burning, discharge, foreign body sensation, itching and light sensitivity.

Snellen chart Standard chart with letters, numbers, or symbols printed in rows of decreasing size used by eye care professionals in distance visual acuity testing. The chart was invented by Dutch ophthalmologist Hermann Snellen.

soft contact lenses Contacts made of gel-like plastic containing varying amounts of water.

solution Product used to clean, disinfect and store contact lenses.

spatial frequency In optics and other fields, a measure of how often a repeating structure (such as a vertical line or bar) appears within a given unit of distance.

spherical A contact lens design that is like a sphere and is fairly common; in contrast, topic lenses for astigmatism are football-shaped and are less common.

spots Small, cloudy specks in the eye that become noticeable when they fall in the line of sight.

stereopsis Three-dimensional vision, enabling depth perception.

strabismus A misalignment of the eyes: the eye don't point at the same object together. Crossed eyes (esotropia) are one type of strabismus; "wall-eyes" (exotropia) are another. The exact cause is unknown, but appears to be a problem with the eye muscles. Strabismus can affect depth perception.

stroma The cornea's middle layer; it consists of lamellae (collagen) and cells, and makes up most of the cornea.

sty A small red bump on the edge of the eyelid caused by an infected gland. Additional symptoms include eyelid pain, eyelid swelling, eye pain or discomfort, foreign body sensation, light sensitivity and tearing.

subconjunctival hemorrhage Bleeding from blood vessels on the surface of the eye that leaves a red patch. This common problem can be caused by sneezing, coughing, high blood pressure, trauma and more.

surgery complication Complications from cataract surgery, LASIK or other eye surgeries can result in a variety of symptoms, including blurred vision, ptosis, foreign body sensation, halos around lights, light sensitivity, eye pain or discomfort, red or pink eyes, vision loss and an iris defect.

suspensory ligament Also called zonule of Zinn. Membrane of fibers (zonules) that holds the eye's lens in place.

Tay-Sachs disease Hereditary disorder resulting from a deficiency of the enzyme hexosaminidase. Symptoms include blindness, delayed development, seizures and paralysis. Tay-Sachs disease often results in an early death.

thrombosis Blood clot. Such coagulation of the blood can occur anywhere in the circulatory system of the body, including the heart, arteries, veins and capillaries.

tonic pupil Dilated pupil that reacts sluggishly to light, due to damage to the ciliary ganglion from trauma, viral infections or other causes. The cause is sometimes unknown ("Adie's tonic pupil").

toric A lens design with two different optical powers at right angles to each other for the correction of astigmatism.

trabecular meshwork Porous, spongy tissue within the eye, through which fluids pass.

trichiasis Condition in which the eyelashes grow inwardly (towards the eye).

trichotillomania Disorder characterized by compulsive hair or eyelash pulling. The exact cause is not known.

trifocal A lens design that has three focal areas: a lens for close work or reading, a lens for mid-distance viewing or arm's length, and a lens for faraway viewing or driving.

20/20 vision Many eye care practitioners consider this the average visual acuity for human beings, but humans can see as well as 20/15 or even 20/10. People with 20/40 vision can see clearly at 20 feet what people with 20/20 vision can see clearly at 40 feet. In most of the United States, 20/40 is the lowest uncorrected acuity required for a driver's license.

ultraviolet (UV) The invisible part of the light spectrum whose rays have wavelengths shorter than the violet end of the visible spectrum and longer than X rays. UVA and UVB light are harmful to your eyes and skin.

vascular birthmark A pink, red or purple mark (flat or slightly raised), typically on an infant's face or neck, caused by a malformation of blood vessels. Types of vascular birthmarks include capillary hemangiomas ("stork bites" or "angel's kisses") and port-wine stains.

vascular problem Problems with your body's vascular system (i.e., blood vessels, arteries and so on) can include hardening of the arteries, high blood pressure, a clot, an aneurysm, an embolus, etc. These problems can sometimes affect the eyes, resulting in such symptoms as blurred vision, a bulging eye, double vision, eye pain or discomfort, a red or pink eye, eyelid swelling and vision loss.

visual acuity Sharpness of vision, usually as measured with the use of a Snellen chart. 20/20 is considered normal visual acuity, though some people can see even better (such as 20/15 or 20/10).

vitreous body Part of the eye between the lens and the retina, containing a clear jelly called the vitreous humor.

vitreous detachment Separation of the vitreous from the retina, caused by age-related vitreous shrinkage. Floaters are the typical symptom, but some people experience flashes of light as the vitreous tugs or causes traction on the retina prior to complete separation.

vitreous hemorrhage Bleeding that goes into the vitreous from nearby parts of the eye, such as from leaking retinal blood vessels. Causes include diabetic retinopathy, trauma, a retinal tear or detachment, vitreous detachment and retinal vascular occlusion (blockage in the retina's vascular system). Symptoms include sudden blurring or loss of vision, and new floaters.

wavefront Describes technology used to "map" how the eye processes images, enabling correction through surgery or lenses for obscure vision errors.

wear schedule How long you wear your contact lenses: either daily wear (you remove the lenses each night) or extended wear (you may sleep with them in). It's important to differentiate between wear schedule and replacement schedule - that is, how often you discard and replace your lenses.

white dot syndrome One of a group of inflammatory conditions that are characterized by white dots in the retina and choroid. You may also hear these syndromes called by their specific names, such as acute posterior multifocal placoid pigment epitheliopathy, multiple evanescent white dot syndrome, birdshot chorioretinopathy or multifocal choroiditis and panuveitis. In some cases, the cause is unknown; in others, it's believed to be an autoimmune disorder. Symptoms can include blurred vision, loss of color vision, floaters, light sensitivity, metamorphopsia and vision loss.

raparound Also called "wrap" for short. Type of eyeglass or sunglass frame that curves around the head, from the front to the side.

xanthelasma A yellow, fatty spot or bump on the inner corner of either the upper eyelid, the lower one or both eyelids, often caused by a lipid disorder such as high cholesterol.


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