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Eye Health Glossary

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aberration

Imperfections in an optical imaging system such as the cornea or the crystalline lens such that the clarity of an image is reduced. In Custom LASIK, many higher order aberrations are being accounted for, which leads to visual clarity following Custom LASIK that is unprecedented.

accommodation

Accommodation is the ability of the crystalline lens within the eye to change shape in order for vision to be clear when viewing near objects. With age, the crystalline lens becomes less flexible and cannot accommodate as easily. This condition is known as presbyopia.

alcaine

Alcaine is the commercial name for the drug proparacaine, which is often used by optometrists and ophthalmologists as an anesthetic eye drop. When instilled in the eye, it will sting for a few seconds, and then it will be anesthetized (frozen). These drops are used when the doctor wishes to perform a procedure that requires contact with the cornea, such as contact tonometry and gonioscopy, or when a patient is suffering from intense pain caused by a corneal abrasian.

amaurosis fugax

A sudden, temporary loss of vision in one eye, which is usually caused by an obstruction in blood flow to the eye. Amarausis fugax can be a warning sign to future permanent vision loss, so it is important to see your doctor as soon as possible.

amblyopia

Also known as “lazy eye”, amblyopia is an eye condition in which the vision in one eye is significantly reduced (but not as a result of an eye disease) and cannot be corrected with glasses or contact lenses. Because the vision in that eye is not useful, the brain focuses its attention on the other eye exclusively. Amblyopia can result from a strabismus (crossed eye).

ametropia

Ametropia is the word used to describe any refractive condition in which the eye does not properly focus light onto the retina to form a clear image. Anyone who needs glasses or contact lenses to see clearly is ametropic. Myopia, hyperopia, and astigmatism are all examples of ametropia.

amsler grid

The Amsler grid is a way of measuring distortion (metamorphopsia) as well as blind spots (scotomas) in vision. It is a small grid with a dot in the middle. To use the Amsler grid, hold it 33 cm away from you, close one eye and focus the other eye on the dot in the middle. Without moving your eye, take note of any breaks or distortions that may appear in the lines of the grid. The Amsler grid is one of the standard tests used to assess vision in patients with macular degeneration.

angioid streaks

Small breaks in a layer of the retina known as Bruch's membrane. Connective tissue disorders such as pseudoxanthoma elasticum can result in formation of angioid streaks.

angle closure glaucoma

A type of glaucoma in which there is a sudden and severe rise in intraocular pressure caused by a sudden blockage in the drainage system of the eye. Aqueous humor builds up in the eye, leading to a spike in IOP. Patients who experience an angle closure attack will present with a red, painful eye and blurred vision. Learn more about glaucoma.

aniridia

A hereditary condition in which the iris is either completely or partially absent. Individuals with aniridia experience poor vision, extreme sensitivity to light (photophobia), and potentially nystagmus.

aniseikonia

An eye condition in which the image formed by each eye is different in size (and sometimes shape as well). This may be caused by a difference in refractive power between the eyes (anisometropia).

anisocoria

An eye condition in which the pupils are unequal in size. While it is possible that is is completely benign, all cases of anisocoria must be treated as emergency situations, as there is a potential that it could indicate a life-threatening situation.

anisometropia

A refractive condition in which the refractive error differs between the eyes. As long as the difference between the eyes is not great, this generally poses no problem, but if there is a large difference, children who have anisometropia can potentially develop amblyopia (lazy eye).

anomalous trichromat

An individual who has all three cone photoreceptors functioning, but one (or more) is abnormal. In most cases, the wavelength sensitivity spectrum of one particular cone photoreceptor is shifted so that the combined responses of all three cone receptors produces the perception of colors that are different than that of a person with normal color vision. Learn more about Color Vision.

anophthalmos

Complete absence of an eyeball.

anterior angle

The angle that is formed where the cornea meets the iris. Aqueous humor drains through the trabecular meshwork in this area. Closure of the angle can lead to obstruction of the aqueous humor drainage system, which results in angle closure glaucoma.

anterior chamber

The chamber within the eye between the iris and the cornea. The anterior chamber is filled with aqueous humor.

anti-reflective coating

A thin film that coats the surface of an eyeglass lens and reduces both back-glare into the wearers eyes as well as the glare that can be seen by others who are looking at the person with glasses. By designing the film to be of a particular thickness and index of refraction, the film causes destructive interference in the beams of reflecting light that would normally cause glare.

antisometropia

A refractive condition in which one eye is myopic and the other eye is hyperopic.

aphakia

A condition in which the natural crystalline lens has been removed. Before the introduction of intraocular lenses, all cataract surgery patients were aphakic. Since the crystalline lens is responsible for 1/3 of the refracting power of the eye, nearly all cataract patients found themselves having to wear very strong eyeglasses following surgery. With IOLs, however, cataract surgery patients today are enjoying vision without the need for glasses.

aqueous humour

The clear, watery liquid contained within the anterior chamber and posterior chamber. Aqueous humor is continually produced by the ciliary body and nourishes the cornea and the crystalline lens. Aqueous humor drains through the trabecular meshwork.

arcus

The latin term for “arch.” Often used to describe the arch-shaped whitish deposit that can seen within the cornea. Aka arcus senilis.

arcus senilis

The opaque, creamy arch-shaped lipid deposit that is often seen in the elderly. Often arcus senilis can occur without pre-existing systemic complications, particularly if it is bilateral; however, arcus senilis may be a sign of elevated or poorly controlled lipid levels within the body, especially if it exists in young people.

argyll robertson pupil

Small, irregular pupil that does not respond to light, but does respond normally to near targets (normally, when a person views a near target, the pupil constricts). Individuals with tertiary syphillis tend to have an Argyll Roberston pupil.

artificial tears

Artificial tears are eye drops that can be used to relieve symptoms of dry eye. They are available in many different formulations, from gels to liquids, to ointments. They can be used as often as necessary, but provide only temporary relief. Learn more about more permanent solutions for dry eye syndrome.

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aspheric

Not spherical; used in high-power eyeglass lenses. This enables the lenses to be much thinner and lighter, which is an important goal for many people who have high prescriptions.

asthenopia

More commonly referred to as eye strain, asthenopia is a common eye complaint for individuals with uncorrected hyperopia, computer vision syndrome. Asthenopia is often accompanied by ocular fatigue and headache.

astigmatism

A common refractive condition where the cornea is irregularly shaped such that it is shaped more like a football than a spherical ball. Eyeglasses or toric contact lenses with different powers in two meridians are needed to correct for astigmatism. Learn more about astigmatism.

atopic

An inherited tendency to develop allergic reactions. Examples of such occurrences are eczema, asthma, and hayfever (which is often responsible for most cases of atopic conjunctivitis).

atropine

For ophthalmic purposes, atropine is a drug available as an eye drop that acts as a mydriatic (dilates pupils) as well as a cycloplegic. Its effects are long-lasting, which makes it a poor drug for the purposes of a regular eye exam, but it is useful in the treatment of amblyopia and offers an alternative to patching.

autorefractor

An electronic machine that measures the refractive error of the eye as well as the corneal curvature. It can be found in most optometric and ophthalmic practices and is usually used as part of the pre-exam (before the patient sees the doctor.

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