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The rotation of an eye away from the midline, or centerpoint of vision. Also the diverging of the eyes away from each other.

What are the symptoms?
A cross-eyed appearance; One or both eyes is turned away from the nose.

What is the treatment?
Eye exercises can aid in improving eye muscle strength and can resolve some cases. In cases of infants and children, glasses may be prescribed. Eye drops, ointment or special lenses called prisms can also be used to straighten the eyes. Finally, Eye muscle surgery can correct such deviations and restoration of binocular vision is often possible.

Additional keywords and misspellings:

obduction abducsion abduct abducton duction abductian strabismus

A localized collection of pus; an infected pocket of tissue.

What is the treatment?
Treatment may vary according to the location and nature of the abscess but may often consist of topical antibiotics.
The ability of the eye to focus and maintain a clear image as objects are moved closer. The ciliary muscles of the eye contract and the zonules relax, causing the flexible crystalline lens to "round up" and increase its optical power. When a person ages and begins to lose accommodation, it is referred to as presbyopia .

The absence of pigment; albinism; total color blindness.
ah kro' mah ti zm

The condition of being totally color-blind or color-less.
a koh ree' ah

The absence of the pupil of the eye.

Visual ACUITY refers to a standard that represents the clearness or sharpness in vision or sight. Visual acuity may be referred to as the "resolution" in vision.
The most common standard for measuring visual acuity is Snellin Acuity. The Snellin standard is usually used to define "distance" visual acuity. Under the Snellin standard the object is placed 20 feet from the observer. The measurement is always in reference to this 20 foot distance. As an example, consider a person who is said to have 20/40 visual acuity. 20/40 means that the person being tested had to move up to 20 feet from the object in order to see a letter which was actually placed 40 feet from the observer. The test objects that are traditionally used to subjectively test visual acuity are: Capital letters, Rotating "C"s, Tumbling "E"s (for children).

Another standard for measuring visual acuity is Jaeger Acuity. This is defined in terms of a metric reference. The Jaeger standard is most often used in measuring "near point" vision, rather than distance vision.
ah sy' oh NOP see ah

The inability to distinguish blue tints.

The rotation of the eye toward the midline of the body (in the direction of the nose).

How do you get it?
It can be inherited, or it may be caused by trauma, certain diseases, and sometimes eye surgery.

What is the treatment?

Treatment for adduction usually consists of eye patching, vision therapy or, in severe cases, surgery to correct the weakened muscles.
ah deh NO mah

A benign tumor originating from, or resembling, glandular epithelium. It is of endocrine or exocrine origin.
Adie's Pupil
Adie's Pupil, or Adie Syndrome is a rare neurological disorder affecting the pupil of the eye. It is a condition in which the pupil does not react normally to bright light due to impaired nerve function. Adie's Pupil usually does not interfere substantially with normal vision.

Who can get it?
It occurs mostly in middle age women. The cause is unknown, but it is thought to be a form of neuropathy, which means the nerves that control the pupils and the reflexes selectively degenerate.

Some people think this is due to an attack by a virus, while other medical opinions believe it is an auto-immune disorder, meaning that the immune system makes antibodies that attack these specific nerves. Other causes may include giant cell arteritis, neurosyphillis, alcoholism, diabetes, and herpes zoster.

What are the symptoms?
In most patients the pupil is dilated (larger than normal) and slow to react to light on nearby objects. In some patients, however, the pupil may be constricted rather than dilated. There may be light sensitivity in the affected eye due to the pupil's impaired function in helping to reduce light intensity by constricting in bright light.

The pupil also helps to focus light in the eye, and sometimes the nerves that control the lens in the eye may also be involved, so as a result the vision from the affected eye is often blurry. The patient adapts to the large pupil over time.

Absent or poor reflexes are also associated with this disorder.

What is the treatment?
Adie Syndrome is neither progressive nor life threatening, nor is it disabling.

Additional keywords and misspellings:
addie's addy's ady adie ady's Adie's Pupil Adie's Syndrome Adie's Tonic Pupil Holmes-Adie Syndrome Papillotonic Psuedotabes Tonic Pupil Syndrome
The appendages or adjoining anatomical parts of the eye (eyelids, conjunctiva, extraocular muscles and glands of the eye).
An after-cataract, or secondary cataract, is one that forms following cataract removal surgery. Typically it occurs when a piece of the cataract remains or when scar tissue has formed an opacity.

Who can get it?
Anyone. Secondary cataracts typically can occur in about 30% of all cataract surgery cases.

What are the symptoms?
Blurring in a portion of your vision that should have been clear following cataract surgery.

What is the treatment?
The procedure to remove a secondary cataract is quite simple. A Yag laser is used to eliminate the remaining opacity and is quick and painless. The procedure is called a Posterior Capsulotomy.

Additional keywords and misspellings:
aftercataract second cataract posteror yag yaglaser
Agnosia, Spatial
spay'shal ag-no'se-ah

The inability to orientate one's self in space, usually accompanied by visual agnosia, due to a disturbance in the brain.
Allergic Lid Edema
Allergic Lid Edema refers to the eyelid swelling that is typically the result of an allergic reaction to external irritants.

Who can get it?
Anyone can get an ocular allergy.

What are the symptoms?
Sudden severe eyelid swelling after eating certain foods, ingesting certain medicines or after exposure to tanning beds.

What is the treatment?
Eyelids are thin and therefore the swelling may appear more dramatically than in other parts of the body. The retained fluid, however, usually responds quickly to treatment. Ocular medications are often prescribed to prevent the further release of histamines and reduce swelling and redness. Certain eyedrops may sting or burn on application but this is normal.

Cold compresses can also help to reduce swelling and soothe sore eyes. If you are suffering from allergic lid edema, see your optometrist for treatment and home care instructions.
Amaurosis Fugax
am' ah roe sis FUE gaks

The temporary loss of vision in one eye without visible ocular lesions. Amaurosis Fugax may be a sign of a transient ischemic attack (TIA) or can be indicative of an impending stroke.
am bee OCK u ler

A term meaning "with both eyes together", with both eyes in sync.

AMBLYOPIA is commonly referred to as "lazy eye". Amblyopia is a term used to denote poor vision in an eye without any discoverable pathologic condition causing it. Sometimes it is called "Amblyopia ex anopsia"or amblyopia from disuse. It has been likened to the phrase "If you don't use it, you lose it". If vision is less than that of the other eye, it may be clinically diagnosed as Amblyopia.It is a condition in which visual acuity is reduced and not completely correctable by refractive methods.

Who can get it?
Many people with amblyopia have a problem with reading. They frequently are slow readers or dislike reading, in spite of a satisfactory I. Q.

Sometimes Strabismus( "crossed eyes") is the basic cause of the amblyopia. Strabismus means that both eyes do not line up together to present a unified image for the individual. In this case, the individual unconciously, blocks out the vision in one eye to prevent a double image (diplopia). As such, the treatment must include an evaluation of the strabismus first, before any help can be expected regarding the amblyopia. When the double vision problem is corrected, perhaps with "prisms" in glasses, there is no longer a reason for the unconcious blocking of the vision in one of the eyes. The result is that the amblyopia spontaneously improves.

What are the symptoms?
Poor vision in one eye; crossing of one eye toward or away from the nose.

What is the treatment?
Treatment for amblyopia frequently consists of patching of the good eye to try to stimulate usage of the affected eye. This is best initiated at the earliest possible age (age 10 or younger). Treatment may still be effective at older ages, however it is generally regarded as much more difficult. Vision Therapy (orthoptics) may be included in the treatment regimen to further stimulate development of vision in the affected eye.

Patching of the affected eye in children under age 4 can be very difficult. They will typically try to remove the patch, not recognizing the long term benefits from any treatment. Creative methods are often times employed to accomplish the treatment. These may range from adhesive type patches that are difficult to remove, to a contact lens that has been blackout out to prevent sight in the good eye.
An imperfection in the refractive power of the eye, such as nearsightedness, farsightedness, or astigmatism.

Additional keywords and misspellings:
ameotropia ametropea
Amsler grid
A chart featuring horizontal and vertical lines used to test vision. This test is extremely useful in diagnosing macular degeneration.
an ah trope' ee ah

The persistent and abnormal upturning of the visual axes above the horizontal plane; turning upward.

A tumor composed of lympathic or blood vessels. Forms include Angioma pigmentosum atrophikum, and angiomatosis (Sturge-Weber disease).
A condition in which each pupil is of different size. Simple aniscoria occurs in 20% of otherwise normal individuals and is not a problem. The pupils can vary by a size of 0.3 and 0.5 millimeters.

What causes it?
There are many possible causes of anisocoria, such as medications, Horner's Syndrome, Third Nerve Palsy, Adie Pupil, or damage to the iris.

How is it treated?
Treatment depends on what the cause of the problem was. In simple anisocoria, there is no treatment since it is merely a benign abnormality and not a problem. In the case of a disease or disorder, treatment of the cause will help correct the anisocoria.
A difference in refractive error of the eyes.
An adhesion between the margins of the eyelids.
No eyeball; also called anophthalmos.
Anterior Chamber
The anterior chamber is the fluid-filled space inside the eye between the iris and the endothelium.
Anterior Chamber Hemorrhage
A rupture in the anterior chamber of the eye.
Anti-Reflection Coating
Special anti-reflective coatings are much like those used for fine camera lenses. These coatings are particularly effective for reducing eye fatigue for computer operators and anyone driving at night. And, of course, anti-reflection coatings on lenses enhance appearance by removing all distracting reflections.

Aphakia is a term meaning the natural lens is missing. Absence of a lens is often the result of surgical procedures such as cataract removal but also can be injury-related or more rarely, due to a congenital defect. A person who has had cataract surgery without a lens implant is said to be "aphakic".

Who can get it?
Glasses (refractive treatment) are often very thick (bottle-glass) lens prescriptions. The typical lens powers range from +12 dioptors to +20 dioptors. With this type of lens correction, the visual field is significantly reduced. The individual frequently feels uneasy in driving and other activities which require peripheral awarness and depth perception.

A better treatment for aphakia is contact lenses which can restore the field of vision with minimum distortion and no loss of binocularity or depth perception.

In many cases the best treatment is to have a second operation performed in which an intra-ocular lens implant (IOL) is inserted. The IOL is usually placed behind the iris (Posterior IOL). Sometimes the IOL is located in front of the iris, if vitreous is moving through the pupil (Anterior IOL).

For more information see: Pseudophakia, Cataract and Intraocular Implant

Additional keywords and misspellings: afakia, aphaka, aphakya, afakya, aphakea
Aqueous flare
The abnormal visibility of a beam of light as it passes through anterior chamber; due to increase in protein content of aqueous humor.
Aqueous Humor
ay'-kwee-us hyoo'mur

The clear fluid inside the eye orbit that, under proper level and pressure, keeps the rounded shape to the cornea. This fluid is produced by the ciliary body and drains through the trabecular meshwork. If this fluid doesn't drain properly, pressure builds within the eye and presses on the optic nerve. This condition is called glaucoma.
Arcus Senilis
Arcus Senilis is a hazy ring at the edge of the cornea where the iris meets the white of the eye but does not impair vision.
Artery Occlusion
Retinal artery occlusion occurs when the central retinal artery or one of the arteries that branch off of it becomes blocked by a tiny clot in the blood stream. The blockage decreases the oxygen supply to the area of the retina nourished by the affected artery, causing permanent vision loss. Different types of occlusion include a central retinal artery occlusion and a branch retinal artery occlusion.

Who can get it?
Persons with the following conditions:
· High cholesterol · Heart disease
· Arteriosclerosis · Hypertension
· Diabetes · Glaucoma

What are the symptoms?
Signs of an artery occlusion include a temporary loss of vision prior to the artery occlusion, or sudden, painless and partial or complete loss of vision in one eye .

What is the treatment?
Artery occlusion is diagnosed by examining the retina with an ophthalmoscope.

If it is caught within the first hour and treatment is initiated immediately, recovery is possible in rare cases. However, after that time the risk of permanent vision loss is extreme, and there is no treatment that can restore vision lost from an artery occlusion.
Artificial Silicon Retina
A new device designed to treat Macular Degeneration and Retinitis Pigmentosa has been developed and is under review. Artificial Silicon Retinas™ (ASR) are 2 mm silicon chips about the thickness of paper. They were first implanted in the retinas of three people in 2000. Each chip has 3,500 microscopic solar cells, each with an electrode designed to stimulate remaining retinal cells from underneath the retina in a pattern resembling the light images focused on the chip. The chips are completely self contained and receive their power from the light that enters the eye. They require no wires or batteries.

The chip was invented by Dr. Alan Cnow and his electrical engineer brother, Vincent Chow. For more information on the Artificial Silicon Retina™, please visit the Optobionics website at www.optobionics.com.

Other devices are being investigated. At Johns Hopkins Hospital in Baltimore a device is being developed which involves the use of a small external camera which transmits an image to an implanted chip placed near the ganglion cells.

(Information used with permission from the Optobionics™ corporation)

Additional Keywords/Misspellings:
artificial retina artifical retinal implant optobionics Dr. Chow opto bionics
The A-Scan provides two functions: one is to calculate the axial length (AL) of the eye and the other is to take that axial length along with a keratometer measurement and then calculate the best projected power of the proposed IOL.

The method by which the A-Scan calculates the AL is like radar. A sound impulse is echoed off the back of the eye and the time is takes for the echo to return to the probe is converted into the AL with an oscilloscope-type display.

Additional keywords and misspellings:
ascan a scan diagnostic equipment testing IOL power echo sound radar
Aspheric Lens

A lens that resembles an ellipse, parabola, or other conic section rather than a sphere. It can be designed to improve the fit and comfort of a lens by paralleling the cornea more closely.
Asteroid Hyalosis
Spherical and stellate opacities in the vitreous; made of calcium-lipid combinations.

Astigmatism is the result of having a cornea that is irregular in shape. The cornea is normally round. An astigmatic cornea is oblong or "football" shaped, resulting in a condition that generally causes eyestrain, headaches and blurry vision. Astigmatism is often associated with nearsightedness and farsightedness.

The simple act of reading often creates headaches and eyestrain, since the image is never completely clear. The individual may have to re-read the word several times.

Who can get it?
Heredity plays a role in astigmatism. Other factors which may be responsible for distortion in the eye include: aging, cataracts or a corneal (eye) injury.

What is the treatment?
Treatment of astigmatism is usually accomplished by glasses or special contact lenses. The type of lens is called a "Toric Lens" and has a cylindrical shape to it. Adapting to toric lenses is often difficult for patients. The very nature of the lens creates a distortion which may give the appearance of everything tilting forward, backward or to one side. Lines may appear curved and walls may curve inward or outward. These symptoms are especially true with a first time wearer of astigmatic lenses. This can also be true of someone who has worn these type of lenses all of their life, but only has a change of lens axis.

If there is much of a difference in astigmatism between the two eyes there may be significant spatial distortion, loss of depth perception and headaches.

(contributed by H. Frank Storey, OD)

Additional keywords and misspellings:
astygmatism astigmatizm

Axenfeld-Rieger Syndrome
A rare, congenital ocular disorder in which glaucoma may be present along with a flattened nose and/or developmental defects of the teeth (fewer teeth than normal) and facial bones . There may be some atrophy or lack of coloring of the iris, pituitary problems, cardiac disease,

Who can get it?
A-R syndrome is inherited.

What are the symptoms?
Generally, there are no symptoms. It is often discovered during routine examination. Hazy vision may be a sign of glaucoma. If glaucoma develops, there is a risk of vision loss due to the damage to the optic nerve.

Additional keywords and misspellings:
anterior chamber cleavage syndromes Axenfeld’s anomaly Axenfeld’s syndrome Rieger’s anomaly Rieger’s syndrome
The Eye Encyclopedia is a collection of eye care terminology created by practicing optometrists and ophthalmologists. The information provided is not intended to be a substitute for regular medical care or to diagnose or treat any medical condition, and should be used only as a supplemental source of information. Please consult your doctor if you have any questions or concerns about your eye health.