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Glossary of common eye terms

A

Aberrometer

A device that can identify common and more obscure vision errors by measuring the way light travels through the optical system.

Accommodation

The eye's ability to switch focus when seeing from one distance to another.

Accommodation disorder

Is blurred or double vision, headache, eyestrain, fatigue and problems concentrating and / or reading.

Presbyopia

A common accommodation disorder and eventually affects just about everyone as it relates to diminished vision caused by aging.

Albinism

is a condition where a person or animal lacks pigment in both the skin and eyes. Albinos 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 of albinism include light sensitivity, nystagmus, blurred vision, vision loss and strabismus.

Amaurosis fugax

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

Amblyopia

or "lazy eye" is the undeveloped central vision in one eye, causing a reliance on the dominant eye. Strabismus is the leading cause of amblyopia, followed by anisometropia. Patients suffering from amblyopia may be found squinting and / or closing one eye to see, along with blurred vision in one eye and / or vision loss.

AMD or ARMD

age-related macular degeneration) is an eye disorder characterized by the gradual loss of central vision due to a damaged macula.

Aniridia

is the absence or partial absence of the iris and is typically a congenital eye disorder. Additional symptoms to aniridia may include poor vision and photophobia (light sensitivity).

Anisocoria

refers to unequal pupil size. Causes of anisocoria include glaucoma, head or eye trauma, intracranial tumor and / or the infection of membranes surrounding the brain. Intraocular Surgery can also be culprit. A small percent of the population is born with unequal-sized pupils with no known cause, as anisocoria has not been traced to congenital birth defects.

Anisometropia

A condition where eyes have significantly different refractive powers, resulting in a contact lens Rx that differs greatly from one eye to the next.

Anophthalmos

An often severe abnormality of the eyes. Anophthalmos may be congenital or due to trauma, infection or other causes. Symptoms include reduced depth perception and diminished peripheral vision, depending on the degree or stage of anophthalmia.

- Primary anophthalmia

A complete absence of eye tissue due to a failure of the part of the brain that forms the eye.

- Secondary anophthalmia

The eye starts to develop and for some reason stops, leaving the infant with only residual eye tissue or extremely small eyes which can only be seen under close examination.

- Degenerative anophthalmia

The eye started to form and, for some reason, degenerated. One reason for this occurring could be a lack of blood supply to the eye

Anterior chamber

The part of the eye behind the cornea and in front of the iris and lens.

Antibody

Antibodies are natural proteins in the body that fight infection and disease. The more antibodies (within reason) your body produces, the stronger your immune function.

Antioxidant

By now you've heard or read a lot about the benefits of antioxidants. They are free-radical fighting compounds found in fruits, vegetables, juices, whole foods and dietary supplements. Antioxidants guard the body against damaging unpaired electrons that destroy cells. Research indicates that heightening levels of antioxidants in the body may help stave off macular degeneration and many other eye diseases.

AR Coating

A thin anti-reflective coating applied to a lens to reduce the amount of glare and reflective light that reaches the eye.

Aqueous Humor

Clear fluid between the cornea and the iris in the front of the eye. Aquesous Humor provides the cornea and eye lens with nutrients to help keep eyes healthy.

Arcus

An opaque arc or ring around the peripheral cornea that represents fatty or oily deposits in the cornea. It is usually seen in elderly people and is called arcus senilis. Arcus juvenilis is seen in people younger than 40 and often indicates high levels of cholesterol in the blood.

Aspheric

Ashperic contact lenses and eyeglasses are popular among people who have strong prescriptions because they are thin, lightweight and reduce distortion and eye magnification. Aspheric contact lenses can work to correct problems such as astigmatism and others where a multifocal lens is preferred.

Asteroid hyalosis

A benign condition that creates suspended particles within the eye's interior and detectable during a thorough eye exam. Not to be confused with floaters, asteroid hyalosis is comprised of yellowish fatty particles moving within the eye's vitreous. The condition appears associated with aging and does not obstruct vision.

Astigmatism

Instead of being round, the eye's cornea is curved and the eye shaped like a football rather than a baseball. The result is blurred vision caused by light reflecting off two points on the retina rather than just one.

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B

Beta titanium

A material used in the making of high-grade ophthalmic frames. Beta-titanium eyeglass frames are strong, flexible and can last for years.

Bifocal

A double purpose lens for the seeing of both near and far. Both eyeglasses and contact lenses are available in bifocal. Some brands of bifocals are called "Progressives," as the line differentiating the two lenses is nearly invisible.

Binocular vision

The ability of both eyes to work together to achieve proper focus, depth perception and range of vision, often associated with 20/20 vision or perfect eyesight.

Biocompatible

The ability of contact lenses to coexist with eye tissue without harming it, a direct result of the research and development of contact lens materials to sit on the eye's cornea without causing a toxic or immunilogical response that could potentially harm the eye.

Bioptic telescopic lenses (BTL)

Magnifying devices attached to eyeglasses that provide extreme magnification.

Blepharitis

is an uncomfortable disorder recognized by inflammation of the eyelid(s) around the eyelashes. Certain types of skin disorders can cause Blepharitis. Symptoms include irritated eyelid crusty eyelashes and eyelids, a foreign body or burning sensation, eyelid pain or discomfort, dry eyes and eyelids, swelling, grittiness and tearing.

Blepharochalasis

Droopy eyelid caused by recurring swelling. Systemic conditions linked to blepharochalasis include renal agenesis, vertebral abnormalities and congenital heart disease. Blepharochalasis occurs more often in the young than it does the old. The cause of blepharochalasis is relatively unknown.

Blepharoconjunctivitis

Inflammation of the eyelid and conjunctiva, the clear mucous membrane consisting of cells and underlying basement membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. Infections and allergic reactions are among the causes of blepharoconjunctivitis. Symptoms include pink eye, swelling eyelid, discomfort, tearing, stickiness and grittiness.

Blepharospasm

Involuntary blinking disorder that eventually progresses to both eyes. The cause of blepharospasm remains a mystery, but doctors believe it to be triggered in some way by the central nervous system. Blepharospasm can result in a type of functional blindness for sufferers who can keep their eyes open long enough to attain focus or a modicum of visual acuity.

Bowman's membrane

Corneal layer between the eye's epithelium and stroma.

Bridge

In the optical world the bridge is the part of eyeglasses that extends across the bridge of the nose.

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C

Cable temple

Eyeglass that wrap around the ears so as to stay on your face better.

Canaliculus

are tiny channels at the beginning of the eye's tear ducts through which tears drain until exiting into the nose.

Canaliculitis

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

Carotenoid

A fruit and vegetable pigment often referred to as an antioxidant that protects eye tissue against damaging free radicals known to breakdown eye tissue. Carrots contain high levels of carotenoids, which is why they are associated with healthy vision.

Cataract

Clouding of the natural lens of the eye, often associated with aging. Cataract is also associated with risk factors, such as exposure to ultraviolet rays, smoking, steroid intake and diabetes. Cataract symptoms include blurred vision, glare, halos around lights, colors that are less bright, a cloudy spot in your line of sight and in some cases temporary vision improvement.

Cavernous sinus problem

Problems in the cavernous sinus include tumors, aneurysms and clots. Symptoms include ophthalmoplegia, chemosis and bulging eye. You may also experience a red eye and vision loss. The cavernous sinus is located at the base of the cranium and contains the carotid artery and cranial nerves.

Cellulitis

refers to inflammation of tissue around the eye. Pre-septal cellulitis affects the lid and outer areas of the eye with symptoms including a red, swollen eyelid, lid pain and / or discomfort. Orbital cellulitis affects the eyeball and inner eye areas with symptoms that include a bulging eye, red swollen eyelid, discomfort and / or diminished vision. Orbital cellulitis is considered an ocular emergency.

Central serous retinopathy

An eye disorder in which fluid collects under the macular area of the eye and disrupts central vision. Symptoms include blurred central vision and metamorphopsia and some patients develop floaters. The cause of central serous retinopathy is unknown.

Cerebral cortex

Outer portion of the brain where certain vision processes take place.

Chalazion

is a small bump on the eyelid caused by an obstructed meibomian gland, a sebaceous gland located at the rim of the eyelid and responsible for the supply of meibum, an oily substance that prevents evaporation of the eye's tear film. Besides physical symptoms, symptoms of chalazion include light sensitivity, tearing and lid swelling and are typically pain free.

Chemosis

Conjunctival swelling often caused by allergy.

Choroid

Blood vessel layers located between the white of the eye and the retina that provide nourishment to the back area of the eye.

Choroidal neovascularization

Abnormal growth of new blood vessels in the choroid, a vascular layer of connective tissue between the eye's retina and sclera. Commonly associated with macular degeneration, choroidal neovascularization can occur as a result of other eye conditions as well. Symptoms include vision loss and metamorphopsia.

Ciliary body

The ciliary body of the eye is the part located between the iris and choroid. Main functions of the ciliary body include accommodation, aqueous humor production and holding the eye lens in place.

CMV retinitis

(cytomegalovirus retinitis) A serious eye infection prone to people with immune problems, such as AIDS. CMV symptoms include floaters, blind spots, blurred vision and vision loss.

Color blindness

a condition resulting in partial or total inability to distinguish specific colors. Color blindness is inherited and more common in men than in women.

Computer vision syndrome

A collection of eye and vision problems related to computer use. Symptoms of computer vision syndrome include eyestrain, dry eyes, blurred vision, red eyes, eye irritation, photophobia and ocular related headaches.

Cone

A photosensitive receptor in the retina of the eye that helps to identify and distinguish colors.

Conjunctiva

is the thin, clear mucous membrane that lines the sclera (white of the eye) and inner surface of the eyelid.

Conjunctivitis

also known as "pinkeye" or "pink eye" is the inflammation of the conjunctiva. Causes of conjunctivitis are either infectious or allergic. Symptoms include burning, discharge, dryness, itching, light sensitivity, pain stickiness, discomfort and excessive tearing.

Contact lens problems

range from minor to sight-threatening. Problems with contact lenses include protein build-up, lens debris and ripped or chipped lenses. Symptoms of contact lens problems 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

is the eye's ability to distinguish an object from its background or an adjacent object.

Cornea

The clear part of the eye covering the iris and pupil that lets light into the eye and permits sight. When the cornea is shaped like a football and not round, a condition called astigmatism is present.

Corneal abrasion

Loss or damage to the epithelial layer (outer layer) of the cornea due to minor trauma. Symptoms include blurred vision, foreign body sensation, grittiness, light sensitivity, eye pain or discomfort, reddening of the eye and excessive tearing. A corneal abrasion can be brought about by contact lens trauma, a sports injury, dirt or otherwise foreign object in the eye.

Corneal dystrophy

A hereditary condition or group of conditions where the cornea loses transparency and the corneal surface is no longer smooth. Symptoms include blurred vision, foreign body sensation, photophobia, eye pain or discomfort and vision loss.

Corneal edema

is the swelling of the cornea typically caused by intraocular surgery, corneal dystrophies, high intraocular pressure and complications with contact lenses. Symptoms include vision loss, halos around lights, a white or cloudy spot on the eye, photophobia, eye pain and foreign body sensation.

Corneal erosion

is the recurring breakdown of the cornea outer layer often caused by a previous corneal abrasion or dystrophy. Blurred vision, foreign body sensation and eye pain and / or discomfort are among symptoms.

Corneal implants

Artificial corneal rings or contacts surgically implanted in the eye to correct vision.

Corneal opacity

A normally transparent cloudy spot on the surface of the cornea. Causes include corneal scar tissue and infection and symptoms include photophobia, vision loss, halos around lights and a grayish or cloudy spot on the eye.

Corneal ulcer

A corneal abrasion that has been infected, often caused by contact lens wearers with bad hygiene. A corneal ulcer is an ocular emergency and includes symptoms such as photophobia eye discomfort or pain, red eyes, cloudy spots on the cornea and excessive tearing.

Cranial nerve

cranial nerves that impact eye health and vision are the second cranial nerve (optic nerve), third (oculomotor), fourth (troclear), sixth (abducens) and seventh (facial) cranial nerves. The optic nerve carries stimuli from the rods and cones to the brain. The third, fourth and sixth cranial nerves aid eye muscles in controlling eye movement. The seventh cranial nerve works with the facial muscles to control facial movement, such as the opening and closing of eyelids.

Crossed eyes

better known as strabismus or misalignment of the eyes is when one or both eyes point inward on the face toward the nose.

Cystoid macular edema

(CME) is the swelling of the eye's macula, resulting from the collection of an excessive amount of fluid.

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D

Dacryoadenitis

is inflammation of the tear gland caused by viral or bacterial infection. Symptoms include a dry eye, swollen red eyelid and / or swelling around the eyes.

Dacryocystitis

refers to inflammation of the tear sac caused by dacryostenosis (tear duct blockage). Discharge, sticky eye, eye pain or discomfort, swelling, redness and excessive tearing are among symptoms.

Dacryostenosis

is a clogged or blocked tear duct characterized by excessive tearing, discharge and or grittiness.

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).

Dermatochalasis

Drooping eyelid resulting from the loss of elasticity in aging skin.

Descemet's membrane

Corneal layer located between the eye's endothelium and stroma.

Diabetic maculopathy

Diabetes-related eye disease that results in swelling and the leakage of fluids and fats into the macula, obstructing focus and central vision. Severe diabetic maculopathy can result in loss of central vision and even blindness.

Diabetic retinopathy

Typically a symptom of advanced or long-term diabetes, diabetic retinopathy is the leaking of retinal blood vessels that affect the macula or retina. Symptoms include blurred near and double vision, floaters, retinal and / or vitreous hemorrhages and metamorphopsia (objects appear distorted). Later stages of diabetic retinopathy have been known to result in vision loss.

Diabetic vitreous hemorrhage

Bleeding into the gel-like interior of the eye, originating from blood vessels weakened by diabetes, diabetic vitreous hemorrhage is the bleeding into the gel-like interior of the eye (vitreous humor). Surgery is sometimes required to relieve the condition.

Diopter

Unit of measure used in eyeglass and contact lens prescriptions that indicates the power of a lens and its refractive (light-bending) power. A negative number refers to nearsightedness; a positive number to farsightedness (i.e. someone prescribed -8.00 diopter lenses is very nearsighted, while in contrast a patient prescribed with +0.75 diopter lenses is only slightly farsighted).

Diplopia

is when two images of the same object are perceived by one or both eyes, in essence seeing two of everything, also known as double vision.

Disposable contact lenses

are contact lenses that are thrown away after a short period of time (i.e. daily, 1-2 weeks, 1-3 months) as opposed to what most refer to as "frequent replacement" lenses which are discarded monthly or quarterly.

Dk/t

is the measurement of a contact lens's oxygen transmissibility.

Double vision

Medically called diplopia(see definition above).

Drooping eyelids

A condition (also called ptosis) where only the upper eyelid(s) sag. Drooping eyelids is both a congenital conditions and can occur later in life as a result of eyelid muscles failing to properly lift the eyelid.

Druse

Small yellow or white deposit in the eye and are sometimes diagnosed as signs of macular degeneration.

Dry eye

Exactly how it sounds, dry eye characterized by lack of lubrication and moisture in the eye-most often temporary in nature and easily treated. Persistent dry eye, however, should be looked at by your eye care professional as it may be keratoconjunctivitis sicca, a chronic, more serious form of dry eye requiring advanced treatment. Contact lenses wearers who suffer from dry eye often may want to consult their eye care professional on the benefits of switching contact lens materials. Contact lens wearers who suffer from dry eye also tend to use contact lenses beyond their compliance and / or keep them in their eyes for excessive periods of time.

Dry eye syndrome

Dryness due to reduced quantity of the eye's tear film-typically chronic. Symptoms of dry eye syndrome include aging, various systemic diseases and long-term contact lens wear. Eye pain, foreign body sensations, photophobia, itching and irritation can also accompany dry eye syndrome.

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E

Ectropion

is an abnormal turning out of the lower eyelid that exposes the inner, conjunctival side of the eyelid. Ectropion is common with aging and can accompany eye or eyelid discomfort or pain and / or red eye or excessive tearing.

Emmetropia

refers to eyes with good vision and ones where light reflects correctly and images are processed by the eye clearly.

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

refers to layers of cells inside the cornea.

Enophthalmos

is the sinking or receding of the eye into the eye socket. Causes include utero problems, trauma and inflammation.

Entropion

is when the eyelid turns in causing eyelashes to rub on the surface of the eye-usually a result of aging. Eye or lid pain or discomfort, foreign body sensation, red or pink eye, itching, tearing and vision loss are among additional symptoms.

Enzymatic cleaner

A contact lens cleaner recommended for cleaning frequent replacement lenses, such as weekly or monthly disposables. Enzymatic contact lens cleaners come in both tablet and liquid form.

Epiretinal membrane

Also called a macular pucker by eye care professionals, an epiretinal membrane is a thin layer of scar tissue on the retina caused by a variety of conditions including vitreous detachment. Epiretinal membrane is often asymptomatic in early stages and and develop into metamorphopsia.

Episclera

The outer layer of the white of the eye (sclera) that loosely connects to the conjunctiva.

Episcleritis

A swelling of the episclera, the cause of which is relatively unknown. However, episcleritis has been associated with autoimmune diseases. Red or pink eye, eye pain, photophobia and tearing are among symptoms.

Epithelium

is comprised of the cornea's outer layer of cells.

Esotropia

is a type of strabismus and occurs when one or both eyes point inward and appear "crossed."

Exotropia

is the opposite of esotropia where eyes appear walleyed and point outward to the sides of the face. Exotropia is another form of strabismus.

Extended wear

contact lenses have been approved by the FDA to be worn without removal for seven to 30 days, depending on brand and compliance. Extended wear contact lenses can be left in eyes overnight. Thirty-day extended wear contact lenses are often referred to as "continuous wear." The abbreviation EW is common when referring to extended wear contact lenses.

Eye care practitioner

commonly referred to as Eye Care Professionals on yourlens.com include optometrists (ODs), ophthalmologists (MDs specializing in eye care) and opticians licensed in certain U.S. states to fit and prescribe contact lenses. In the United States, ODs 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.

Eye herpes

is a synonym for ocular herpes, which is a recurrent viral infection that can lead to inflammation and scarring of the cornea. Ocular herpes is not a sexually transmitted disease. The severity of ocular herpes ranges from from the less serious herpes keratitis to more serious forms that cause blindness.

Eye tumor

Eye Tumors, both benign and malignant, include dermoid cyst, capillary hemangioma, cavernous hemangioma, choroidal melanoma, retinoblastoma, rhabdomyosarcoma and lymphoma. Eye tumors typically appear as a growth occurring in or next to the eye.

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F

Farsightedness

or hyperopia is when near objects are blurry without corrective lenses while objects in the distance appear focused.

FDA

The Food & Drug Administration is the U.S. government body that oversees medical devices, medications, contact lenses, intraocular lenses and eye drops. In the United States, these products must be approved by the FDA before they can be marketed.

Fixation

The eye's ability to �fixate' on an object. Synonyms could include gaze or stare.

Floaters

As we age, little pieces of retina break loose and float in the vitreous of the eye. This is what most refer to as floaters. Most floaters are harmless and result in little more than inconvenience. However, certain floaters aren't as harmless and may be the result of vitreous detachments that must be diagnosed and treated as soon as possible. Yearly eye exams can help detect dangerous floaters. Talk to your eye care professional.

Fluorescein

Fluorescein dye solutions aid doctors in detecting corneal lesions and testing for dry eye syndrome. Fluorescein is a compound that becomes bright and turns fluorescent yellow-green when in contact with alkaline substances. No doubt you are familiar with fluorescent light bulbs-same concept.

Fluorescein angiography

is an imaging test useful in diagnosing conditions such as age-related macular degeneration and the abnormal growth of blood vessels in the eye's retina.

Foreign body sensation

is the sensation that something is in your eye, when no foreign substance is present.

Frequent replacement contact lenses

called also planned replacement are contact lenses that are thrown away after a moderately short period of time. Disposable contact lenses typically refer to contact lenses worn from one day to two weeks, while frequent replacement lenses are discarded monthly or quarterly.

Fungal keratitis eye infection

A fungus known as Fusarium was the source of a 2006 outbreak of fungal eye infections among contact lens wearers. Fusarium can be found in soil, water, and organic matter including plants. Although rare for a fungus to infect the eye, severe damage can result if left untreated and lead to corneal implant.

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G

Glaucoma

is an eye disease characterized by elevated intraocular pressure, causing optic nerve damage and peripheral vision loss. Most people have no initial symptoms of chronic or open-angle glaucoma, but can develop peripheral vision loss, headaches, blurred vision, difficulty adapting to darkness and halos around lights. Another form of glaucoma, closed-angle glaucoma, may come with additional symptoms such as eye pain, a pupil unresponsive to light, redness, nausea and bulging eye.

Graves' ophthalmology

is an autoimmune eye disorder associated with abnormalities of the thyroid gland. Eyelid retraction, bulging eyes, light sensitivity, eye pain or discomfort, double vision and /or vision loss and limited ability to move the eyes are among symptoms.

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H

Hard contact lenses

is an obsolete name for what are now called Rigid Gas Permeable (RGP) lenses or Gas Permeable (GP) lenses, which are made from a much softer, more breathable contact lens material.

Herpes of the eye

is another term for eye herpes or ocular herpes.

Heterochromia

is a condition where eyes are different colors or one has more pigment than the other.

High-index lens

is a type of lens with a higher refraction index, meaning that light travels faster through the lens to reach the eye than with traditional glass or plastic. Because a high-index lens is denser not thicker, the same amount of visual correction occurs with less material and a thinner lens.

Hyperopia

is the medical term for farsightedness and occurs when light rays focus behind the retina rather than on it, resulting in blurred near vision in addition to eyestrain and occasional squinting.

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I through P

I

Idiopathic

A medical condition with no apparent explanation and most often associated with conditions that happen suddenly, i.e. "After ruling out all the possibilities, the sudden swelling of his eye seemed idiopathic."

Intraocular lens

(IOL) is an artificial lens designed to replace the natural lens of cataract patients. Similar to a contact lens, an intraocular lens has a built-in refractive power tailored-made to suit the patient's visual condition.

Intraocular pressure

(IOP) is the amount of pressure inside the eye as determined by the amount of aqueous humor (gel-like substance) inside. High IOP, also known as ocular hypertension, can be a sign of glaucoma.

Iris

The colored part of your eye that lies between the cornea and the lens. The iris acts as a diaphragm to widen or narrow the pupil, thereby controlling the amount of light that enters the eye. The amount of pigment in your iris is what determines the color of your eyes.

Iristitis

refers to inflammation of the iris.

Ischemia

can lead to eye stroke and sudden vision loss. Ischemia is characterized by poor blood flow caused by clots in veins and arteries that deprive tissue of oxygen and nutrients.

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J

Jaundice

is the yellowing of skin and eyes caused by heightened levels of bilirubin, a type of pigment. Jaundice is associated with a variety of conditions including hepatitis and cirrhosis that invade the liver, gallbladder and bile ducts.

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K

Keratectomy

is the surgical removal of part of the cornea.

Keratitis

is a condition characterized by corneal inflammation, notably caused by infection or otherwise inflammatory reason. Symptoms of keratitis include eye discomfort, photophobia, foreign body sensation, grittiness and excessive tearing.

Keratoconjunctivitis

Inflammation of the cornea and conjunctiva together.

Keratoconjunctivitis sicca

known also as dry eye syndrome, a chronic lack of eye lubrication and moisture.

Keratoconus

Degeneration of the cornea resulting in a type of irregular astigmatism that may be genetic in nature-doctors aren't sure. Blurred vision is the first sign of keratoconus.

Keratoplasty

a general term for plastic surgery of the cornea, such as shrinking the collagen in the cornea to reduce farsightedness or installing corneal transplants designed to treat keratoconus.

Keratotomy

Incision of the cornea.

Keratometer

An instrument that measures the curvature of the cornea. Keratometers help capture measures needed to fit contact lenses, identify dry eyes or perform keratoplasty.

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L

Lacrimal plug

is a device used to block openings at the end of tear ducts as part of a medical procedure to keep eyes moist.

Leber's congenital amaurosis

refers to an inherited condition characterized by blindness or vision loss. Doctors believe the cause to be a degenerative retina or that photoreceptors in the retina may not develop properly.

Lens dislocation

refers to the full or partial displacement of the eye's lens caused by trauma. Lens dislocation can also be inherited or occur as a result of certain systemic conditions. Blurred or double vision are among the symptoms of lens dislocation and the condition can lead to glaucoma.

Leukocoria

better known as white pupil. Congenital cataract, retinoblastoma, intraocular infection, Coat's disease and retinopathy of prematurity are among the causes.

Limbus

is the boundary area connecting the cornea and the white of the eye (sclera). Together, the limbus, cornea and sclera form the eye's outermost layer.

Low vision

is sight that cannot be satisfactorily corrected with glasses, contact lenses or surgery. Low vision usually results from glaucoma, macular degeneration or an otherwise debilitating eye disease.

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M

Macula

The middle part of the retina that allows us to see objects with great detail.

Macular degeneration

is a disorder characterized by a gradual loss of central vision. The exact cause is unknown, but can be related to genetic predisposition, smoking and other health risk factors. Macular degeneration sometimes isn't noticeable in the early stages. It begins with blurred, distorted or shadowy vision prior to vision loss.

Macular edema

refers to the swelling of the central portion of the retina.

Macular hole

occurs in the eye's macula. Doctors believe one cause is the shrinking of the vitreous in the aging process. Symptoms include blurring or a blind spot in central vision.

Maculopathy

the pathological term for macular disease such as age-related macular degeneration.

Madarosis

is the loss of eyelashes and / or eyebrows. Causes include infections, metabolic disorders, blepharitis, certain drugs, lupus erythematosus and trauma.

Medial rectus muscle

is the muscle that moves the eye toward the nose.

Meibomian gland

is located in the eyelid. The meibomiam gland produces the oily outer layer of the three-layer tear film that lubricates the eye.

Meibomianitis

Inflammation of the meibomian glands. A common cause is rosacea and symptoms include red or pink eyelid margins, red eye, dry eyes, a burning sensation and swelling.

Melanin

is human pigment responsible for the iris' color as well as the color of skin, hair and genitalia.

Melanosis

is characterized by melanin deposits in the skin and / or eyes.

Metamorphopsia

is characterized by distorted vision where straight lines may seem curved, bent or wavy, or objects appear larger or smaller than actual size. Metamorphopsia is an eye disorder typically caused by conditions or diseases that affect the eye's macula and retina.

Microcornea

refers to an abnormally small cornea.

Microkeratome

is a small surgical tool used to cut the cornea.

Microphthalmia

is congenital defect resulting in an abnormally small eye or eyes the cause of which remains unknown. Historically, microphthalmia can result in blindness or reduced vision, but normal vision is possible if eyes are nearly normal in size.

Migraine

headache is severe and can cause visual disturbances. Eye and vision symptoms include blurred vision, ptosis, light halos and flashes, photophobia, eye pain, discomfort, blind spots in central vision and other visual disturbances. Migraine headaches involving visual disturbances are often referred to as ocular migraine and / or ophthalmic migraine, which may or may not come with headache.

Mixed astigmatism

Abnormal curvature of the cornea that causes focusing problems at both near and far distances.

Monochromatic

refers to one wavelength of light, as opposed to the many wavelengths of light found in varying colors or in a rainbow.

Monofocal

is a type of eyeglass lens, contact lens or otherwise intraocular lens that has only one area through which the eye can focus.

Monovision

is a vision correction method for presbyopic patients where one eye is corrected for nearsightedness and the other for farsightedness, either through contact lenses, eyeglasses or refractive surgery.

Multifocal

is a type of intraocular lens, spectacle lens, or contact lens design with more than one area through which the eye focuses, such as bifocals or trifocals, and enables sight at multiple distances. Multifocal lenses are typically prescribed for people with presbyopia, a vision disorder characterized by a progressively diminished ability to focus on near objects with age.

Myasthenia gravis

is the weakening of voluntary muscles, believed to be autoimmune in nature. Symptoms include double vision and eyelid ptosis. Myasthenia gravis patients sometimes have non-eye symptoms as well, such as difficulty in swallowing or restrictions in arm and leg mobility.

Myokymia

Common eyelid twitch brought on by stress or fatigue in most cases.

Myopia (nearsightedness)

A condition in which the length of the eye is too long, causing light rays to focus in front of the retina instead of on it, resulting in blurred distance vision. Additional symptoms include eyestrain, poor night vision and squinting.

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N

Nanometer

Abbreviated as nm, a nanometer is a measurement of length equal to one-billionth of a meter. Wavelengths of light are measured in nanometers. Eyeglass and sunglass lens manufacturers use nanometers to describe the different types of light that may pass through or be blocked by a lens, whether it blue light, visible light, ultraviolet light or otherwise.

Nearsightedness

(myopia)A visual condition in which visual images come to a focus in front of the retina, resulting in poor vision when attempting to focus on distant objects.

Neuroblastoma

is a cancer that develops from nerve cells found in several areas of the body. Neuroblastoma most commonly arises in and around the adrenal glands, which have similar origins to nerve cells and sit atop the kidneys. However, neuroblastoma can also develop in other areas of the abdomen and in the chest, neck and pelvis, where groups of nerve cells exist. Neuroblastoma most commonly affects children age 5 or younger, though it may rarely occur in older children and adults. Neuroblastoma is the most common cancer in babies and often has a very good prognosis in children younger than 1.

Neuroretinitis

A condition characterized by inflammation of the optic nerve and retina, caused by infection in most cases. Symptoms include blurred vision, headache, floaters, eye pain or discomfort, vision loss and loss of color vision.

Nickel

is one metal used in the manufacture of eyeglass frames. Nickel is also a component of alloy compounds used in the making of eyeglass frames to which many people are allergic. Eyeglass wearers allergic to nickel are encouraged to look into metal frames made from titanium, metal alloys that don't contain nickel or eyeglass frames made of plastic or acrylic.

Nose pads

located on either side of the bridge of your eyeglasses help support your eyeglasses and keep them comfortable on your face.

Nystagmus

is characterized by rapid and involuntary eye movement. Nystagmus can result in blurred vision and may be symptomatic of other causes.

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O

OD

is the abbreviation for "oculus dexter," the Latin term for "right eye" and found on your contact lens or eyeglass prescription.

Ocular herpes

is a recurring viral infection associated with inflammation and scarring of the cornea. Ocular herpes range from the less serious herpes keratitis to more severe forms that can lead to complete vision loss. Ocular herpes is not a sexually transmitted disease.

Ocular hypertension

occurs when the intraocular pressure of the eye is elevated above normal levels. Ocular hypertension may lead to glaucoma if left untreated.

Ocular migraine

also known as ophthalmic migraine and eye migraine is a visual event that usually accompanies a migraine headache-or it may occur with no headache at all! Visual phenomena includes temporary spots or flashes, curve-shaped elements or other wavy lines or flickers that last from minutes in less severe cases and up to 72 hours in the most extreme.

Onchocerciasis

aka "river blindness," is caused by a parasitic worm most often contracted from the bites of blackfliess and buffalo gnats in various parts of the world, such as South America, Africa, and Southeast Asia. Inflammation, bleeding and other problems in the eye can result.

Ophthalmologist

is a medical doctor (MD) who specializes in the eye and is licensed to perform eye exams, prescribe medications, suggest treatments and perform surgeries.

Ophthalmoplegia

is characterized by paralysis of the eye muscle. Stroke, multiple sclerosis, eye tumors, problems with thyroid, recurring migraines and progressive supranuclear palsy are among causes. Symptoms of Ophthalmoplegia include ptosis, nystagmus and / or double or blurred vision. In its most painful stages ophthalmoplegia is characterized by pain or headache behind the eye.

Opsoclonus

also known as dancing eyes, opsoclonus is characterized by rapid and involuntary eye movement occurring frequently and without pattern. Opsoclonus is associated with Opsoclonus-Myoclonus Syndrome, a rare autoimmune disorder said to affect one in ten million people per year and in roughly 2 percent of children diagnosed with neuroblastoma.

Optic

is a general term that refers to matters of the eye, vision or seeing.

Optic nerve

carries electrical impulses from photoreceptors in the retina to the visual cortex in the brain, enabling the formation of coherent images in the brain.

Optic nerve head

also known as the optic disc, the optic nerve head is where the optic nerve enters the retina causing a break or blindspot in the visual field.

Optic nerve problem

can be characterized by eye pain or discomfort, blurred vision, nausea, floaters and / or headache as a result of swelling of the optic nerve and / or optic nerve tumors.

Optician

(s) in the United States fit eyeglasses, sunglasses and other specialty eyewear. Although opticians are not doctors in the U.S., many states certify and license opticians to fit contact lenses. Primarily, opticians fill prescriptions issued by optometrists and ophthalmologists and often have equipment on premises to grind ophthalmic lenses and put them in frames without ordering from a lab.

optometrist

is a doctor of optometry (ODs) in the U.S. and is authorized to examine eyes for vision and health problems and to prescribe glasses and fit contact lenses. Optometrists can prescribe certain ophthalmic medications and are known to take part in pre- and postoperative eye care. Optometrists must complete four years of post-graduate optometry school to achieve a doctorate and be licensed in the United States.

Orbit

In anatomy, the orbit is the round cavity in which an eye is located in the skull of a vertebrate, better known as the eye socket.

Orbital pseudotumor

Causes unknown, an orbital pseudotumor often mimics the symptoms of a tumor and is an inflammatory mass in tissues around or behind the eye. Bulging eye and / or pain or eye discomfort around the eye is the first sign of orbital pseudotumor.

Orthokeratology

is a procedure in which patients are fit with special gas permeable contact lenses to reshape the cornea and correct errors like nearsightedness. The process often requires that patients wear the gas permeable lenses at night.

OS (Oculus Sinister )

is the latin abbreviation for "left eye" and is seen most frequently by patients on contact lens and eyeglass prescriptions.

OU

is the latin abbreviation for "oculus uterque," the Latin term for "each eye." With regards to contact lens and eyeglass prescriptions, OU means "both eyes." OU is also used as an abbreviation for "oculi unitas" or "oculi uniter," meaning both eyes working simultaneously together.

Overconvergence

is characterized by eyes pointing too far inward on the face when attempting to focus on near objects, which often results in blurring.

Overflow tearing

is commonly caused by a blocked tear duct, a congenital condition in infants and developmental condition in older adults. In adults, overflow tearing can be related to poor eyelid function and result in excessive tears and mucus.

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P

Papilla

Small bump where the optic nerve exits the eye.

Papilledema

is a condition characterized by swelling, accompanied by compression of the optic nerve head, which can lead to a medical emergency. Bleeding around the optic nerve and unusually high levels of cerebrospinal fluid pressure are known causes of papilledema. Trauma, infection and various types of autoimmune disorders are also causes.

Papilloma

Most often caused by virus, eye papillomas typically appear on the eyelid, and sometimes on the conjunctiva (inside eyelid). Papillomas are usually benign in nature and may be raised or flat and can vary in colors from yellow to pink to brown or black.

Pars plana

in anatomy is the posterior part of the eye's ciliary body, an area located between the iris and choroid. Main functions of the ciliary body include accommodation, aqueous humor production and holding the eye lens in place.

Pediculosis

Lice infestation most often caused by contact with a person or bedding already infected with pediculosis. Nits (white or gray eggs), lice feces (reddish-brown), blue bite marks, blepharitis, conjunctivitis and visible lice can occur when lice infest the eyelid and eyelashes. Some people develop keratitis as a result.

Penetrating keratoplasty

also known as a corneal transplant is when the circular area of a healthy cornea is transplanted from donor to recipient. A penetrating keratoplasty may result from trauma, keratoconus or other eye disease.

Peripheral vision

technically peripheral vision is defined as the edges of your visual field. Most refer to peripheral vision as the ability to see objects to the side of us.

Phakic

When the eye still has a natural lens it is referred to as phakic. When the natural lens is removed during cataract surgery or other eye surgery, the eye is referred to as aphakic.

Phoropter

is an eye examination device that uses various combinations of lens powers to determine the extent of eye correction needed to achieve 20/20 vision.

Photoablation

a surgical procedure in which ultraviolet radiation is used to remove eye tissue.

Photochromic

is a len's ability to adapt or change lens color when exposed to varying degrees of light. For example, transition lenses can be referred to as photochromic.

Photokeratitis

better known as " sunburn of the cornea," photokeratitis can result in blurred vision, discomfort and photophobia. Temporary vision loss resulting from photokeratitis is often referred to as snow blindness.

Photophobia

(sensitivity to light) Photophobia has many causes. Signs of photophobia include squinting and or eye pain or discomfort when confronted with high levels of light, inside or out.

Photopsia

Photopsia has many causes and is typically characterized by flashes of light and / or spots or floaters seen at the edges of the visual field. A detached retina can result in photopsia as can a vitreous detachment when the eye's gel-like interior begins to shrink and pull against the retina.

Photoreceptor

Classified in human retina as cones and rods, photoreceptors are light-sensitive cells found in the eye's retina-cones control color vision and are located in the central retina, with rods located outside the central retina, controlling black and white vision in low-light scenarios.

Pinguecula

is characterized by a thick yellowish lesion on the conjunctiva near the cornea often caused by the leakage of certain blood proteins and resulting in protein deposits.

Plano

a lens with no corrective power is a plano lens. The term is frequently applied to contact lenses worn for cosmetic purposes only and to non-prescription sunglasses.

PMMA

(polymethyl methacrylate) a lens material most notably used in the manufacture of hard contact lenses. In contrast to materials used in the manufacture of modern gas permeable lenses PMMA did not allow sufficient amount of oxygen to reach the eye and has been rendered obsolete.

Polarized lenses

typically block ultraviolet rays and block or reduce glare. The term polarized is most frequently associated with polarized sunglasses.

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

a very impact-resistant form of plastic used in the manufacture of spectacle lenses (eyeglass lenses) and frames.

Posterior chamber

is the area or part of the eye located behind the iris and in front of the lens.

Presbyop

The medical term for a person having difficulty reading small print and seeing near objects.

Presbyopia

Persons affected by presbyopia have problems focusing at all distances. The condition most notably begins at middle-age and is often accompanied by eyestrain, headaches, squinting and the inability to see objects clearly on a day to day basis.

Prescription lenses

are lenses that provide corrective action. Prescription lenses can refer to both eyeglasses and contact lenses.

Prism

A prism bends light and is typically made from glass or transparent plastic In optics, a prism refers to a lens with precise geometric configurations that enable light to be reflected in certain ways and / or split white light into various wave lengths and / or colors.

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.

Prosthetic

In the optical world, a prosthetic most often refers to a prosthetic contact lens surgically implanted to replace the eye's cornea.

Pterygium

is a triangular fold of tissue on the sclera that may eventually grow over part of the cornea as result of overexposure from the sun or other elements. Some with pterygium experience no symptoms while others experience blurred vision, redness and / or irritation.

Ptosis

also known as drooping eyelid, ptosis is caused by dysfunction of the levator muscle that lifts the eyelid. Ptosis can be both congenital and caused by the aging of the levator's connective tissue.

Puncta

are the tiny openings at the end of tear ducts that allow for drainage.

Punctal plugs

are often inserted in tear ducts to stop excessive drainage and to allow the eye to moisten properly and avoid dry eye syndrome. Punctal plugs are tiny devices made of plastic.

Pupil

The dark center of the eye that regulates the amount of light received by the retina.

Pupillary distance

is the distance between the center of each pupil. Pupillary distance is an essential measurement when properly fitting eyeglasses so that lenses are positioned properly over respective pupils. A faulty measurement of pupillary distance can result in the poor or inadequate vision correction of eyeglasses.

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Q through Z

R

Refraction

test occurs during an eye examination the results of which are used to determine the lens power needed for maximum vision correction.

Refractive error

occurs when light rays don't refract normally from the cornea to the retina. Refractive error can result in nearsightedness, farsightedness and / or astigmatism.

Replacement schedule

refers to how often you should throw away old contact lenses and replace them with new ones. Contact lens replacement schedules are based on scientific research and often take into account contact lens materials and their ability to maintain their corrective powers. For example, terms such as daily disposable, weekly disposable, monthly disposable - all refer to contact lens replacement schedules; not to be confused with terms such as daily wear (remove before bed) or extended wear (you can sleep in your contact lenses) replacement schedule refers to lens replacement, not type of wear.

Retina

is the sensory membrane in the back of the eye. Photoreceptors in the retina transform light into electrical signals which are then transmitted to the brain by way of the optic nerve.

Retinal detachment

Depending on cause and severity, retinal detachment is a medical emergency requiring immediate treatment. Aging, surgery, trauma, diabetic retinopathy and other conditions impacting the eye are causes for retinal detachment. Symptoms of retinal detachment include floaters, flashes, shadows and or blurred vision and loss of vision.

Retinal tear

refers to a tear or split in the retina, commonly caused by vitreous detachment. Symptoms include floaters and light flashes.

Retinitis

is characterized by inflammation of the retina. Blurred vision, metamorphopsia, floaters and vision loss are among symptoms of retinitis.

Retinitis pigmentosa

Resulting in nightblindness and diminished peripheral vision, retinitis pigmentosa is typically inherited and characterized by progressive degeneration of the retina.

Retinopathy of prematurity

involves the abnormal growth of blood vessels in the retina and is common among premature babies.

Retinoschisis

is characterized by the retina splitting into layers, causing blurred vision. Retinoschisis is either inherited or caused by small cysts developing in the eye. Floaters are a side effect.

RGP

(Rigid Gas Permeable) is a type of contact lens (also known as Gas Permeable (GP) contact lenses) made of a breathable plastic and custom-fit to the shape of the cornea. Gas permeable lenses have replaced now obsolete hard contacts, which did not allow for the sufficient transmissibility of oxygen to the eye.

Rhegmatogenous

arises from a break or tear in the retina or otherwise retinal detachment.

River blindness

medically referred to as onchocerciasis, river blindness is caused by a parasitic worm most often contracted from the bites of blackfliess and buffalo gnats in various parts of the world, such as South America, Africa, and Southeast Asia. Inflammation, bleeding and other problems in the eye can result.

Rod

A Rod in optical terms refers to the photosensitive receptor in the retina that aids vision in low light conditions.

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S

Sclera

(the white of the eye) is the outer coat of the eyeball that surrounds the optic nerve at the back of the eyeball.

Scleritis

is most commonly caused by autoimmune disorders and characterized by inflammation of the sclera (white of the eye). Autoimmune disorders are the most common cause. Symptoms include a red or pink eye, eye pain, light sensitivity, tearing and blurred vision.

Scotoma

refers to a blind spot within the eye's field of view.

Segment

refers to the near vision part of a pair of bifocals.

Single vision

A single vision lens is a lens that maintains the same power across the entire lens, in contrast to a bifocal or multifocal lens that offers more than one lens power.

Sjogren's syndrome

is an autoimmune disorder characterized by dry mouth and dry eyes. Additional eye symptoms include burning, discharge, foreign body sensation, itching and light sensitivity.

Snellen chart

is the eye chart used during eye examinations to assess visual acuity. The Snellen Chart was invented by Dutch ophthalmologist, Hermann Snellen and features letters, numbers and symbols printed in rows of decreasing size.

Soft contact lenses

are contact lenses made of gel-like plastic that contain varying amounts of water. Contact lens materials include a number of petroleum based acrylic and plastic transparent compounds approved by the FDA.

Soft contact lens solution

refers to cleaning solutions designed to clean contact lenses. For wearers of daily disposables, no soft contact lens solution is needed

SPF

(sun protection factor) is the number value indicating the strength of UV sun block. 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

is the name given to a contact lens designed to fit over a normal-sized cornea. In contrast, toric lenses are for football shaped corneas and used in the correction of astigmatism.

Spots

are typically cloudy specks in the eye that fall into the line of sight.

Spring hinge

Type of eyeglass frame hinge more flexible than a regular hinge, making frames more durable.

Stereopsis

Three-dimensional vision that enables depth perception.

Strabismus

is a misalignment of the eyes, meaning they don't point at the same object together. Esotropia ("crossed eyes" eye points inward) is one type of strabismus and exotropia ("wall-eyes" eye points outward) is another. The exact cause of strabismus is unknown, but is traced to problems with eye muscles and can adversely impact a person's depth perception.

Stroma

The eye's stroma occupies the majority of the cornea and consists of collagen and cells. The stroma is the cornea's middle layer.

Stye

is a small red bump on the edge of the eyelid caused by an infected gland. Symptoms include swelling, discomfort, foreign body sensation and tearing.

Subconjunctival hemorrhage

refers to the bleeding of blood vessels on the surface of the eye, leaving a red patch on the sclera. Subconjunctival hemorrhage is a common problem often caused by sneezing, coughing, high blood pressure and / or trauma and usually heals over time.

Supranuclear palsy

(progressive), also called Steele-Richardson-Olszewski syndrome, is a brain disorder that causes serious problems with walking, balance and eye movements. Although the cause is unknown, progressive supranuclear palsy results from deterioration of cells in areas of your brain that control movement. Progressive supranuclear palsy is a rare disorder that slowly worsens over time. It usually affects adults over the age of 60, though some people are diagnosed as young as age 40. While progressive supranuclear palsy is not life-threatening itself, it can lead to life-threatening complications such as pneumonia and swallowing problems.

Suspensory ligament

is the membrane of fibers that holds the eye lens in place.

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T

Temple

is the part of the eyeglass frame that runs from the ear to the lens. Known also as the "arm" of a pair of glasses.

Titanium

is a very strong metal alloy used in the making of durable eyeglass frames. The use of titanium in making eyeglass frames continues to grow as titanium is lightweight, durable and in many cases hypoallergenic.

Tonic pupil

is a dilated pupil that reacts slowly to light, due to damage caused by trauma, viral infections or other causes.

Toric

A toric lens is used in the correction of astigmatism and offers two optical powers at right angles from one another.

Toxoplasmosis

Ocular toxoplasmosis causes inflammation of the eye's interior and can lead to uveitis. Toxoplasmosis is an infection most often contracted from a parasite found in undercooked meat and feces. Toxoplasmosis likely occurs in persons with compromised immune systems and is characterized by flu-like symptoms, such as swollen lymph nodes and muscle aches.

Trabecular meshwork

is a collection of porous, spongy tissue located along the drainage angle of the eye through which fluids exit the eye.

Trachoma

is characterized by a chronic infection of the eyelid and cornea and typically passed from one individual to the next and sometimes transmitted by flies. Trachoma is rather unpleasant, as eyelashes scrape the cornea and eyelids become scarred and start to turn inward. Over time, the eyelid becomes scarred and turns inward. Trachoma can lead to visual impairment and even blindness if left untreated.

Trauma

in the optical world refers to an eye injury resulting from a poke, punch or blow to the eye or head. Depending on the severity of trauma, symptoms can include blurred vision, bulging eye, a burning sensation, double vision, dry eyes, floaters, photophobia and / or general discomfort. Eye trauma of any type needs to diagnosed immediately (even if just a routine poke by accident) to determine appropriate treatment.

Trichiasis

is a condition in which the eyelashes grow inward towards the eye.

Trichotillomania

is a disorder characterized by compulsive eyelash pulling. The cause of tricholtillomania is unknown The exact cause is not known.

Trifocal

refers to a lens with three focal areas: one for detail work and reading, a lens for mid-distance viewing or arm's length, and a lens for faraway viewing or driving.

20/20 vision

is the average visual acuity most eye care practitioners consider normal. However, visual acuity varies among humans with some seeing just as well with 20/15 or 20/10 vision. People with 20/40 vision can see clearly at 20 feet what people with 20/20 vision can see clearly at 40 feet.

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U

Ultraviolet

(UV) Ultraviolet rays encompass the invisible part of the light spectrum. UV rays have wavelengths shorter than the violet end of the visible spectrum, but are longer than X rays. UVA and UVB ultraviolet rays are harmful to eyes and skin in cases of overexposure.

Uvea

refers to the middle layer of the eye below the limbus. The uvea consists of the iris, ciliary body and choroid.

Uveitis

is characterized by inflammation of the uvea. Depending on where inflammation occurs, symptoms of uveitis can vary and include eye pain, redness, photophobia, blurred vision and sometimes floaters. Tearing can be a side effect to uveitis, as can pupils responding poorly to light. The cause of uveitis remains unknown in many cases, but the disorder has been traced to immunological deficiencies.

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V

Vascular problem

Although vascular problems in general refer to problems with the body's vascular system (i.e., blood vessels, arteries, etc) and can include hardening of the arteries, high blood pressure, clots, aneurysm or embolus, vascular problems can occasionally impact the eyes in the form of blurred vision, bulging eye, discomfort, pinkeye, swelling and / or vision loss.

Vergence

is the eyes' ability to turn either inward (convergence) or outward (divergence).

Vergence disorder

Convergence insufficiency is the most common type of vergence disorder, the exact causes of which are unknown. Symptoms of vergence disorder can include eyestrain, fatigue, double vision, headache, difficulty concentrating and / or reading.

Visual acuity

typically refers to the sharpness of vision as measured by the 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

is the part of the eye located between the lens and the retina that contains a clear jelly called the vitreous humor.

Vitreous detachment

refers to the separation of the vitreous from the retina caused by age-related vitreous shrinkage. Symptoms of vitreous detachment include floaters--and sometimes flashes of light-- as the shrinking vitreous tugs on the retina prior to final separation.

Vitreous hemorrhage

refers to blood leaking into the vitreous from nearby parts of the eye, such as from ruptured retinal blood vessels. Diabetic retinopathy, trauma, retinal tear or detachment, vitreous detachment and retinal vascular occlusion are among the causes of vitreous hemorrhage. Symptoms include sudden blurring or loss of vision, and new floaters.

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W

Wavefront

is a type of technology used in mapping how the eye processes images, enabling vision correction with eyeglasses, contact lenses or surgery.

Wear schedule

refers to a contact lens schedule, such daily wear (contact lenses are removed each night) or extended wear (contact lenses approved by the FDA for overnight wear); not to be confused with a contact lens replacement schedule that indicates how often contact lenses are discarded.

White dot syndrome

a group of inflammatory conditions characterized by white dots in the retina and choroid. The cause is relatively unknown but show some ties to autoimmune disorders. Symptoms can include blurred vision, loss of color vision, floaters, light sensitivity, metamorphopsia and vision loss.

Wraparound

refers to eyeglass or sunglasses that curve around the head, from the front to the side. Wraparound sunglasses offer eyes extra sun and wind protection by covering the sides of the eyes and face. Because of the curvature of wraparound lenses, most cannot be customized for corrective vision, however new designs and styles, mostly engineered for use by professional athletes and people who live and work in extreme climate conditions, have been overcoming this problem.

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X

Xanthelasma

A fatty spot or bump on the inner corner of the upper eyelid that is yellowish in color. Xanthelasma can also affect the lower lid and / or both eyelids, and is often traced to a lipid disorder, such as high cholesterol.

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Z

Zeaxanthin

A carotenoid pigment naturally occurring in yellow or orange plants, such as corn and squash, as well as in dark green, leafy vegetables, such as spinach and collard greens. Healthy blood levels of zeaxanthin have been linked to healthy vision.

Zyl

is short for zylonite, a cellulose acetate (form of plastic) used to produce lightweight spectacle frames. Zyl often appears in laminated form and is layered in different colors to produce various patterns, such as tortoise shell, cheetah and tiger fur patterns.

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