| A | B |
|---|
| ablation | Removal. In vision, ablation refers to the surgical removal of eye tissue to correct a refractive error such as myopia. |
| acetate | Type of plastic often used in eyeglass frames. |
| accommodation | Eye's ability to automatically change focus from seeing at one distance to seeing at another. |
| accommodation disorder | Accommodation refers to the eye's ability to automatically change focus from seeing at a distance to seeing at near. Accommodation disorders have a variety of causes. Symptoms include blurred vision, double vision, eyestrain, headache, fatigue and difficulty concentrating (particularly while reading). |
| acrodermatitis enteropathica | Rare inherited condition characterized by dermatitis, hair loss, diarrhea and zinc deficiency. The most common eye symptom is light sensitivity, but conjunctivitis and other symptoms may also be present. |
| AK | (astigmatic keratotomy) Procedure in which a surgeon cuts the cornea so that is more spherical when it heals, thus reducing astigmatism. |
| albinism | Condition where a person or animal is lacking pigment. Albinos' eyes often have very light blue or pink irises and a pink pupil (due to lack of pigment inside the back of the eye). Visual symptoms include light sensitivity, nystagmus, blurred vision, vision loss and strabismus. |
| 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. |
| amblyopia | Also called lazy eye. Undeveloped central vision in one eye that leads to the use of the other eye as the dominant eye. Strabismus is the leading cause, followed by anisometropia. There are no symptoms. The patient may be found squinting and closing one eye to see; there may be unrecognized blurred vision in one eye and vision loss. |
| 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). |
| angle | In glaucoma terminology, "angle" 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 wherein the eyes have a significantly different refractive power from each other. |
| anophthalmos | Absence of the eye or eyes. Anophthalmos may be congenital, or due to trauma, infection or other causes. Symptoms include 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. For example, certain ANSI standards define 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. |
| antioxidant | Substance that inhibits oxidation and can guard the body from the damaging effects of free radicals. Molecules with one or more unpaired electrons, free radicals can destroy cells and play a role in many diseases. Antioxidants may help prevent macular degeneration and other serious eye diseases. |
| antireflective 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 eye that both provides nutrients and determines intraocular pressure. |
| arcus | An opaque arc or ring around the peripheral cornea that is common among the elderly; it represents fatty deposits in the cornea. |
| Argyll Robertson pupil | Small, irregular pupil, usually caused by syphilis. Argyll Robertson pupils do not respond to light. |
| aspheric | Not quite spherical. Aspheric eyeglass lenses are popular among people who have strong prescriptions because they are thin and lightweight, and reduce distortion and eye magnification. Aspheric contact lenses can work as a multifocal, or to correct a single-vision problem like astigmatism. |
| asteroid hyalosis | Benign condition in which flecks of calcium-rich fats become suspended in the eye's vitreous. The exact cause is unknown, but may be due to aging collagen in the vitreous or decomposition of hyaluronic acid in the vitreous. Asteroid hyalosis typically is without symptoms, but some people experience blurred vision or floaters. |
| 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. Additional symptoms include distorted vision, eyestrain, shadows on letters, squinting and double vision. |
| atopy | Type of allergy where levels of the antibody immunoglobin E are increased; atopy includes rhinitis, asthma, hay fever and eczema. |
| aviator glasses | These frames have a large upside-down teardrop shape and usually have a double-bar bridge. Originally, these were metal-framed sunglasses worn mainly by pilots, but now the shape also comes in plastic and is used for eyeglasses as well. |
| band keratopathy | Opacity of the corneal stroma and Bowman's membrane. Symptoms include vision loss and foreign body sensation. |
| best corrected visual acuity | The best vision you can achieve with correction (such as glasses), as measured on the standard Snellen eye chart. For example, if your uncorrected eyesight is 20/200, but you can see 20/20 with glasses, your BCVA is 20/20. |
| beta titanium | Titanium alloy. Beta-titanium eyeglass frames are both strong and flexible. |
| bifocal | Lens with one segment for near vision and one segment for far vision. The term can apply to both eyeglass lenses and contact lenses. |
| blepharitis | Inflammation of the eyelid(s), typically around the eyelashes. Various types of dermatitis, rosacea and allergic reactions can cause blepharitis. Symptoms include a red or pink eyelid, a crusty lid or lashes, burning, foreign body sensation, eye or eyelid pain or discomfort, a dry eyelid, a dry eye, eyelash loss, grittiness, stickiness, eyelid swelling and tearing. |
| blepharochalasis | Excessive, drooping eyelid skin caused by recurring swelling. Blepharochalasis typically occurs in young people. |
| blepharoconjunctivitis | Inflammation of the eyelid and conjunctiva. Infections and allergic reactions are among the causes. 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. |
| botulism | Serious illness from a toxin produced by Clostridium bacteria (usually Clostridium botulinum). Infant botulism and food-borne botulism are the most common forms in the United States. Symptoms include double vision, blurred vision, ptosis, muscle weakness, difficulty speaking, difficulty swallowing, difficulty breathing and nausea. |
| Bowman's membrane | Corneal layer between the epithelium and the stroma. |
| bridge | The part of eyeglasses that extends across the nose. |
| cable temple | Style of eyeglasses that wraps around the ear, to keep them well-fastened. |
| canaliculitis | Inflammation of a tear duct (or ducts), caused by a bacterial infection. Symptoms of this disorder 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 temporary vision improvement. |
| cavernous sinus problem | The cavernous sinus is located at the base of the cranium and contains the carotid artery and cranial nerves. Problems in the cavernous sinus include tumors, aneurysms and clots. Typical symptoms include ophthalmoplegia, chemosis and a bulging eye. You may also experience a red eye and vision loss. |
| cellulitis | Inflammation of tissue around the eye. Pre-septal cellulitis affects the lid and other "outer" areas of the eye, whereas orbital cellulitis affects the "inner" areas around the eyeball. Pre-septal cellulitis symptoms include a red, swollen lid, swelling around the eyes and eye or lid pain or discomfort. Orbital cellulitis symptoms include a bulging eye and ophthalmoplegia, as well as a red, swollen lid, swelling around the eyes, eye or lid pain or discomfort and a decrease in vision. An orbital cellulitis is an ocular emergency. |
| central island | Refractive surgery complication in which the laser leaves an "island" of corneal tissue in the concave ablation zone. Symptoms include double vision and distortion. |
| 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. Some patients also develop floaters. |
| chalazion | A small bump on the eyelid caused by an obstructed meibomian gland. Additional symptoms include light sensitivity, tearing and eyelid swelling. Chalazia are usually not painful unless they become infected. |
| chemosis | Conjunctival swelling that is often caused by an allergy. |
| choroid | Layer of blood vessels and pigments (usually brown or blue) that lies beneath the sclera (the white of the eye). Often mistakenly called the iris. |
| choroidal neovascularization | Abnormal growth of new blood vessels in the choroid. Choroidal neovascularization is commonly associated with macular degeneration, but it can occur as a result of other eye conditions as well. Symptoms include vision loss and metamorphopsia. |
| CK | (Conductive Keratoplasty) Procedure wherein a surgeon uses radio waves to heat collagen in the cornea's periphery to shrink it and reduce hyperopia. |
| ciliary body | Part of the eye between the iris and the choroid; the three form the uvea. The ciliary body's main functions are accommodation, aqueous humor production and holding the lens in place. |
| clip-on | Type of glasses that attaches to your regular glasses, such as clip-on sunglasses. |
| 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. |
| collagen | Fibrous protein in bones and connective tissue, it is also present in the eye. One type of vision correction surgery heats collagen around the edges of the cornea (which lets light into the eye). This procedure reshapes the cornea, helping it focus light right onto the retina, for clearer vision. |
| coloboma | Cleft, usually due to incomplete embryologic development in utero. An iris coloboma is the most common eye coloboma; the pupil will often look like a keyhole or upside-down pear. Colobomas can also affect other eye structures, such as the eyelid, retina and optic nerve; only iris and eyelid colobomas are visible with the naked eye. Additional symptoms such as poor vision may occur, but are not readily apparent from a parent's perspective. |
| 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. |
| conjunctiva | Mucous membrane that lines the visible part of the eye and the inner surface of the eyelid. |
| conjunctivitis | Inflammation of the conjunctiva, characterized by a pink eye. The cause is either infectious or allergic; the term "pink eye" really refers to the viral variety, but is commonly used for any type of conjunctivitis. Other symptoms include burning, discharge, dryness, itching, light sensitivity, eye 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. |
| contrast sensitivity | The least amount of contrast that you can still see. |
| 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. The corneal surface is no longer smooth. Common forms include map-dot-fingerprint dystrophy, Fuch's dystrophy and lattice dystrophy. 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, typically caused by a previous corneal abrasion or by map-dot-fingerprint dystrophy. 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 so you can see better. The ring can be adjusted and even removed if desired. |
| corneal topography | A corneal topographer shines light onto the surface of the eye, then measures 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. The color map uses blue and green to represent flatter areas of the cornea, while red and orange represent steeper areas. |
| corneal ulcer | An infected corneal abrasion. Frequently found in extended wear contact lens wearers. A corneal ulcer is an ocular emergency. Symptoms include light sensitivity, eye pain or discomfort, a red or pink eye, a white or cloudy spot on the eye and tearing. |
| cranial nerve | One of the 12 pairs of nerves that go from the brain to other parts of the head. Those that affect the eyes and vision are the second cranial nerve (optic nerve), third (oculomotor), fourth (troclear), sixth (abducens) and seventh (facial). The optic nerve carries stimuli from the rods and cones to the brain. The third, fourth and sixth cranial nerves work with the eye muscles to control eye movement. The seventh cranial nerve works with the facial muscles to control facial movement (specifically the closure of the eyelids). |
| cranial nerve palsy | Palsy (full or partial paralysis) of the third, fourth or sixth cranial nerves can result in difficulty moving the eye with such symptoms as eyes that don't point in the same direction, reduced depth perception, double vision, ptosis, vision loss, a dilated pupil that doesn't respond to light and head tilting. Causes include head trauma, diabetes, tumors, aneurysms, infarction (tissue death) and more. |
| 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, typically caused by dacryostenosis. 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, which is characterized by a lot of tearing; you may also have a discharge or a 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 | Also called decentration. Refractive surgery complication in which the laser is not centered on the pupil when it removes tissue. Symptoms include glare, double vision and halos. |
| dermatochalasis | Excessive, drooping eyelid skin caused by a loss of elasticity in aging skin. |
| Descemet's membrane | Corneal layer between the stroma and the endothelium. |
| diabetic retinopathy | Leaking of retinal blood vessels in advanced or long-term diabetes, affecting the macula or retina. Most people have no symptoms at first, but can develop blurred near vision, double vision, floaters, retinal/vitreous hemorrhages and metamorphopsia. In later stages, you can also suffer vision loss. |
| diopter | Unit which measures the refractive (light-bending) power of a lens; eyecare practitioners use it in eyeglass and contact lens prescriptions. A negative number refers to nearsightedness, while a positive number refers to farsightedness. For example, someone with -8.00 diopter lenses is very nearsighted, while someone with +0.75 diopter lenses is only slightly farsighted. |
| disposable contact lenses | Technically, this is any contact lens that is thrown away after a short period of time. Among most eyecare practitioners, "disposable" usage ranges from one day to two weeks, while "frequent replacement" lenses are discarded monthly or quarterly. |
| drooping eyelids | Also called ptosis. Condition in which the upper eyelid(s) only sag. It can be present at birth or caused by a later problem with the muscles lifting the eyelid, called levators. |
| drugs | Many drugs, both legal and illegal, can affect your eyes and vision. These include eyedrops, other topical eye medications, pills and more. Symptoms can include blurred vision, burning, dry eyes, eyelash loss, floaters, halos around lights, light sensitivity, pupils that are dilated, small or unresponsive to light, peripheral or general vision loss and jaundice. |
| druse | Small yellow or white deposit in the eye. Drusen are sometimes signs of macular degeneration. |
| dry eye | Lack of sufficient lubrication and moisture in the eye. Most dry eye complaints are temporary and easily relieved; dry eye syndrome, also called keratoconjunctivitis sicca, is chronic and needs more advanced treatment by an eyecare practitioner. |
| 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. |
| dry skin | Skin that is generally dry may include dry eyelids. |
| 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. |
| endophthalmitis | Inflammation of the interior of the eye, typically caused by an infection from eye surgery or trauma. Endophthalmitis is an ocular emergency. Symptoms include floaters, light sensitivity, eye pain or discomfort, a red or pink eye and vision loss. |
| endothelium | The cornea's inner layer of cells. |
| 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. |
| environmental condition | Air pollution, wind and bright light can irritate your eyes and cause symptoms such as burning, dryness and tearing. |
| 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; also called a macular pucker. Epiretinal membranes have a variety of causes, including vitreous detachment, but the cause is often unknown. In its early stages, an epiretinal membrane is often asymptomatic, but some people have blurred vision. You may also develop metamorphopsia. |
| episclera | Outer layer of the eye's sclera that loosely connects it to the conjunctiva. |
| episcleritis | Inflammation of the episclera. The cause is usually unknown, but episcleritis may be associated with some systemic (e.g., autoimmune) diseases. Symptoms include a red or pink eye, eye pain or discomfort, light sensitivity and tearing. |
| 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. |
| 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." |
| eyecare practitioner | Optometrists (O.D.s) and ophthalmologists (M.D.s) both practice eyecare, but in different ways: O.D.s (Doctors of Optometry) examine eyes for both vision and health problems, prescribe glasses, prescribe and fit contact lenses, and treat some eye conditions and diseases. M.D.s are medical doctors who examine eyes, prescribe glasses and contacts, treat disease and perform surgery. Other non-doctor eyecare practitioners include paraoptometrics, contact lens technicians and opticians. |
| eye tumor | A growth or mass that occurs in or next to the eye. Specific tumors, both benign and malignant, include the dermoid cyst, capillary hemangioma, cavernous hemangioma, choroidal melanoma, retinoblastoma, rhabdomyosarcoma and lymphoma. The cause is dependent on the type of tumor you have. Symptoms can include blurred vision; a bulging eye; double vision; floaters; foreign body sensation; pain or discomfort in the eye, the lid or around the eye; swelling of the lid or around the eye; a red or pink eye; ptosis; vision loss; limited eye or lid movement; a white or cloudy spot on the eye; and an iris defect. |
| farsightedness | Also called hyperopia. To farsighted people, near objects are blurry, but far objects are in focus. |
| FDA | (Food & Drug Administration) A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the U.S., these products must be approved by the FDA before they can be marketed. |
| flap and zap | Slang for LASIK. |
| floaters | A dark or gray spot or speck that passes across your field of vision and moves as you move your eye. Floaters are very common and may look like clouds, strands, webs, spots, squiggles, wavy lines or other shapes. 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. |
| 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 eyecare practitioners, "disposable" usage ranges from one day to two weeks, while "frequent replacement" lenses are discarded monthly or quarterly. |
| 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. |
| 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. |
| heterochromia | Condition where one eye is a different color from the other, or one eye is more than one color. |
| 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. |
| high-index | Type of lens with a higher index of refraction, meaning that light travels faster through the lens to reach the eye than with traditional glass or plastic. It is denser, so the same amount of visual correction occurs with less material (whether glass or plastic) — so the lens can be thinner. |
| histiocytosis | Abnormal proliferation of histiocytes (immune system cells). Common symptoms include bone tumors and skin rashes. If histiocytosis affects the eyes, it causes bulging. |
| 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. 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 | Diaphragm that controls the size of the pupil (an opening that lets light in). Many people believe the iris is the colored part of the eye. Actually, that is the choroid, a pigmented layer beneath the sclera (white of 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 | Also called dry eye syndrome. Chronic 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. The first symptom is blurred vision that doesn't improve enough with glasses (contacts usually work well for a while). You may also have double vision or distorted vision. |
| keratoplasty | Any of several types of corneal surgery, such as shrinking the collagen to reduce farsightedness or transplanting a new cornea to treat keratoconus. |
| keratotomy | Incision of the cornea. |
| lacrimal plug | Also called punctal plug. Device to block the lacrimal punctum (an opening at the end of a tear duct), to keep the eye moist. |
| 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. |
| LASEK | (Laser Epithelial Keratomileusis) Procedure that is similar to LASIK, except that the surgeon cuts a flap in the epithelium only, instead of through the epithelium and part of the stroma. LASEK is used mostly for people with thin or flat corneas who are poor candidates for LASIK, which requires more corneal tissue for success. |
| 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 and hyperopia. |
| lateral rectus muscle | Muscle that moves the eye away from the nose. |
| lead poisoning | Condition resulting from excessive levels of lead in the body. Typically, children get lead poisoning from chewing or sucking on lead paint in older homes (lead paint was banned in the 70s). Some people remain symptom-free, but others may suffer convulsions, paralysis, learning difficulties or abdominal and other pain. Some people can also develop vision loss. |
| 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. Nystagmus is a common symptom. |
| lens | The nearly spherical body in the eye that focuses light rays onto the retina. |
| 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. Blurred vision is a typical symptom, and some people may experience double vision and/or develop glaucoma. |
| leukocoria | White pupil. Causes include congenital cataract, retinoblastoma, intraocular infection, Coat's disease and retinopathy of prematurity. |
| limbus | Boundary area connecting the cornea and sclera; the three form the eye's outermost layer. |
| 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. |
| liver spot | Benign dark spot on the skin, usually brown, that is associated with exposure to sunlight. Liver spots tend to increase in size. |
| low vision | Also called partial sight. Sight that cannot be satisfactorily corrected with glasses, contacts, or surgery. Low vision usually results from an eye disease such as glaucoma or macular degeneration. |
| 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, conjunctivitis and retinal vascular occlusion (blockage in the retina's vascular system). |
| lutein | An antioxidant that is found throughout the body, but is concentrated in the macula. Lutein is believed to help protect the eyes from free radical damage caused by the sun's harmful rays. |
| 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. The exact cause is unknown, but appears to be related to a genetic predisposition, smoking and several other risk factors. Central vision may be blurred, distorted (metamorphopsia) or shadowy before vision loss occurs. |
| macular hole | Hole in the eye's macula; many doctors believe it can be caused by vitreous shrinkage as we age. Symptoms include blurring or a blind spot in central vision and metamorphopsia. |
| maculopathy | Disease of the macula, such as age-related macular degeneration. |
| madarosis | Eyelash or eyebrow loss. Causes include infections, metabolic disorders, blepharitis, certain drugs, lupus erythematosus and trauma. |
| medial rectus muscle | Muscle that moves the eye toward the nose. |
| 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. |
| melanosis | Condition characterized by melanin (pigment) deposits in the skin or eyes. |
| 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. For example, 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. Metamorphopsia is typically caused by conditions or diseases that affect the eye's macula and retina. |
| microcornea | Abnormally small cornea. |
| microkeratome | Small instrument that surgeons use to cut the 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. Visual disturbances alone are also possible; this problem is called an ophthalmic migraine, or migraine without headache. 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. |
| 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. |
| mucormycosis | Fungal infection typically occurring in the sinuses or lungs and mainly acquired by those with compromised immune systems and by diabetics. Symptoms include sinusitis, eye and facial pain, fever, a bulging eye and vision loss. |
| multifocal | Type of spectacle or contact lens design that includes more than one focal area, such as bifocals or trifocals. |
| 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 | Also called 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. |
| 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. |
| nevus | Birthmark, freckle or mole. Nevi are often brownish, but can be other colors as well, such as blue, black, reddish or skin-colored. Nevi can be raised or flat. The exact cause is unknown, but genetics and sunlight exposure appear to be factors. Some people also have freckles on the iris and/or retina. |
| nickel | Metallic element used mainly in alloys. Many eyeglass frames are made of nickel alloy, so people who are allergic should choose a hypoallergenic substitute, such as titanium. |
| 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. |
| OD | (oculus dexter) Right eye. Or, doctor of optometry. |
| 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. |
| onchocerciasis | A medical doctor (M.D.) 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. Tolosa-Hunt Syndrome, often called "painful ophthalmoplegia," is characterized by intense pain behind the eye and a headache. |
| opsoclonus | Rapid and involuntary eye movement that is irregular and chaotic; sometimes called "dancing eyes." Typically seen in Opsoclonus-Myoclonus Syndrome. |
| optician | Opticians are not doctors, but in some states they must complete training and be licensed. And in some states they can become certified, after special training, to fit contact lenses. Most opticians sell and fit eyeglasses, sunglasses, 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 | Part of the eye that carries stimuli from the rods and cones to 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 (O.D.s) 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. O.D.s must complete four years of post-graduate optometry school for their doctorate. |
| orbit | Eye socket. |
| 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 | (oculus sinister) 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. |
| OU | (oculus uterque, oculus unitas or oculus uniter) Both eyes. |
| overconvergence | Condition in which the eyes come too far inward when focusing on a near object, resulting in blurring. |
| overflow tearing | Common congenital condition in infants and developmental condition in older adults caused by a blocked tear duct. In infants, a membrane blocks the tear drainage duct, resulting in excessive tears and mucus. In adults, the cause of the blockage is usually unknown, but can be related to poor eyelid function. |
| papilla | Small bump where the optic nerve exits the eye. |
| papilloma | Usually benign tumor, such as a wart or a skin tag; papillomas may be raised or flat, and can be a variety of colors, such as skin-colored, yellow, pink, brown or black. Eye papillomas are typically on the eyelid, but may also appear on the conjunctiva. The cause of papillomas is felt to be viral. |
| 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. |
| pars plana | Posterior part of the eye's ciliary body. |
| 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. |
| pediculosis | The edges of your visual field. |
| photoablation | Procedure in which a surgeon uses ultraviolet radiation to remove tissue. |
| photochromic | Able to change lens color or darkness/density depending upon the degree of exposure to light. |
| 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. Photophobia has many causes. |
| 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 eyecare 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. |
| PMMA | (polymethyl methacrylate) Old-fashioned hard contacts were made of PMMA, which is not permeable; today's rigid lenses contain other polymers that allow oxygen to reach your eye. |
| polarized lenses | Lenses that block light reflected from horizontal surfaces such as water, to reduce glare. |
| porphyria | Disorder in which the body produces too much of a compound called porphyrin and releases it in the urine, causing a reddish color. Other symptoms include light sensitivity, skin that swells or is sensitive to sunlight, abdominal pain, blisters and muscle weakness. |
| polycarbonate | Plastic that is very impact-resistant, and is thus sometimes used for spectacle lenses and frames. |
| 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 is unable to focus on near objects. It typically begins around age 40. Additional symptoms include eyestrain, headaches and squinting. |
| prescription lenses | Lenses that provide vision correction as prescribed by an eyecare practitioner. |
| 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. |
| propionate | A soft, flexible material that is sometimes used in goggles. |
| protective eyewear | Eyewear made with impact-resistant lenses, usually polycarbonate, that protects the eyes, especially in working situations or sports. |
| protein | All living cells contain these large, complex organic molecules that include enzymes, antibodies, hormones, and other elements that help organisms function. Proteins are present in human tears and can collect on contact lenses, resulting in discomfort and cloudy vision. |
| 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. Some people have no symptoms, while others may have redness or blurred vision. Pterygia that are chronically inflamed can become itchy. |
| 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. |
| 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 surgery | Surgery that corrects visual acuity, with the objective of reducing or eliminating the need for glasses and contacts. Includes radial keratotomy, PRK, LASIK, and corneal implants. |
| replacement schedule | How often you discard and replace your contact lenses: every day, week or two weeks (disposable); or every month, two months or calendar quarter (frequent replacement). It's important to differentiate between replacement schedule and wear schedule. Wear schedule is either daily wear (removed before sleeping) or extended wear (you may sleep with them in). |
| 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 your vision, 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. You may also have floaters. |
| 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. |
| 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. It can be associated with uveitis. |
| river blindness | This parasitic disease is contracted from the bite of a certain fly. Causes blindness if untreated. The scientific name is onchocerciasis. |
| RK | (Radial Keratotomy) Surgical procedure where cuts are made in the cornea in a radial pattern, to flatten the cornea and correct myopia. |
| rod | A photosensitive receptor in the retina that helps you to see in low light. |
| rosacea | Skin condition typically involving the face that is characterized by flushing, red bumps and telangiectasia (dilated, visible capillaries); it is most common among fair-skinned women, who develop it in their 30s through 50s. |
| sarcoidosis | Disease in which granulomas (nodules of inflamed tissue) form in the lymph nodes, lungs, skin and other areas. The cause is unknown. Symptoms include fatigue, weight loss, fever, coughing, uveitis, cranial nerve palsies and skin lesions. Some patients also develop dry eyes. |
| 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. |
| 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. |
| 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. |
| skin cancer | Skin cancer is commonly caused by exposure to the sun's UV rays. Types include basal-cell carcinoma, squamous cell carcinoma and malignant melanoma. In carcinoma, you are likely to have a red or pink bump that bleeds, crusts and scales. In melanoma, the pigmented areas can be raised or flat; they are often brown or black, but can be (or include) other colors as well, such as blue, red, pink or white. Some raised moles are skin-colored. The most common symptoms of a malignant mole follow an ABCD checklist:• Asymmetry: one half does not match the other. |
| soft contact lenses | Contacts made of gel-like plastic containing varying amounts of water. |
| solution | Product used to clean, disinfect and store contact lenses. |
| SPF | (sun protection factor) Number representing the amount of sun something blocks. For example, if you normally begin to burn after half an hour in the sun, a sunscreen with an SPF of 2 should let you stay out twice as long (1 hour), SPF 4 should let you stay out four times as long, and so on. |
| spherical | A contact lens design that is like a sphere and is fairly common; in contrast, toric 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. |
| spring hinge | Type of hinge on eyeglass frames that is more flexible than a regular hinge, making the frames more durable. |
| 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. |
| stroke | An interruption in blood flow to the brain, resulting in tissue death. Blood clots and other obstructions can interrupt the blood flow, as can a ruptured artery. Symptoms include weakness or numbness, particularly on one side of the body, a change in consciousness or mental status, vision loss, double vision and limited eye movement. You may also blink frequently. |
| 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. |
| temple | The "arm" of a pair of glasses, running from the ear to the lens area. |
| titanium | A type of metal alloy that is very strong. Eyeglasses made of titanium are lightweight, durable and often hypoallergenic. |
| 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. |
| toxocariasis | Infection caused by Toxocara worms, which are typically found in cat and dog intestines. The form found in the eyes, ocular larva migrans, can cause vision loss. |
| trachoma | Chronic infection of the eyelid and cornea. It is spread by contact with eye discharge from an infected sufferer. Insects can also transmit the bacteria. Can cause visual impairment and blindness. |
| trauma | Injury, such as from being poked in the eye or hit in the head. Depending on the type of trauma, symptoms can include blurred vision, a bulging eye, burning, double vision, dry eyes, floaters, light sensitivity, pain or discomfort of the eye or around the eye, swelling, a pupil that is dilated or unresponsive to light, vision loss, limited eye or lid movement, ptosis, an iris defect and an eyelid cleft. |
| 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 eyecare 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. |
| uvea | Middle layer of the eye, below the limbus, and consisting of the iris, ciliary body and choroid. |
| uveitis | Inflammation of the uvea. In most cases, the cause is unknown, but infectious or immunological systemic disorders can cause uveitis. Symptoms vary depending on where in the uvea the inflammation occurs; they include mild to strong eye pain, redness, light sensitivity, blurred vision and floaters. You may also experience tearing, a pupil that responds poorly to light or squinting. Specific types of uveitis include iritis, iridocyclitis, cyclitis, pars planitis and choroiditis. |
| 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. |
| vergence disorder | Vergence refers to the eyes' ability to turn either inward (convergence) or outward (divergence); convergence insufficiency is the most common vergence disorder. The disorders' exact causes are unknown. Symptoms include double vision, eyestrain, fatigue, headache, squinting and difficulty concentrating (particularly while reading). |
| 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. |
| 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. |
| wraparound | (wrap) Type of eyeglass frame that curves around the head, from the front to the side. Wraparound sunglasses tend to offer extra sun protection because the lenses usually wrap as well. |
| 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. |
| zyl | Zylonite, or cellulose acetate, is a lightweight plastic often used in eyeglass frames. It often appears in laminated form, with layers in different colors, but it can also be made in mottled patterns to imitate natural tortoise shell or animal skins. |
