Aberration

Distortions, related to astigmatism , that cause the inability of light rays entering the eye to converge (come together) to a single focus point on the retina . Aberration are divided into two main categories — higher-order and lower-order.

Ablation

Surgical removal of tissue, typically using a cool beam laser

Ametropia

Breakage of the refractive system of the eye. It can manifest itself in the form of myopia, farsightedness, astigmatism.

Anisometropia

Condition of the eyes in which they have unequal refractive power.

Aphakia

Absence of the lens of the eye.

Asthenopia

Eye fatigue that occurs during visual overloads; visual acuity remains within normal limits.

Astigmatism

Structural defects of the eye in which the light rays from a viewed object do not meet in a single focal point, resulting in blurred images being sent to the brain. An astigmatic cornea is not perfectly rounded like a basketball but has an irregular shape more like the side of a football. Astigmatism is most often combined with myopia or hyperopia.

Axis

a straight line through the centers of both surfaces of a lens. Visual - a straight line from the object of vision to the fovea of the eye.

Ablation zone

The area of tissue that is removed during laser surgery

Accommodation

Ability of the eye to change its focus between distant objects and near objects

Acuity

Sharpness, acuteness, or keenness of vision

Acute

Occurring suddenly

Adnexa

Accessory structures of the eye, including the eyelids, lacrimal apparatus, etc.

AK

modified form of Radial Keratotomy (RK)

Amblyopia

Dullness or obscurity of sight for no apparent organic reason, therefore not correctable with glasses or surgery. Sometimes called a lazy eye, wherein one eye becomes dependent on the other eye to focus, usually developed in early childhood. Often associated with strabismus

Amsler grid

Hand held chart featuring horizontal and vertical lines, usually white on black background, used to test for central visual field defects

Angle

Drainage area of the eye formed between the cornea and the iris , named for its angular shape, which is why you see the word "angle" in the different glaucoma names

Anterior chamber

Space between the cornea and the crystalline lens , which contains aqueous humor

Anterior ocular segment

Part of the eye anterior to the crystalline lens , including the cornea , anterior chamber , iris and ciliary body

Antioxidants

Micronutrients that destroy or neutralize free radicals, molecules that have been implicated as one causative factor in the stimulation of abnormal cellular reproduction (cancer) and cellular destruction (aging)

Antireflective coating

Coating on the front or back of glasses lenses, which minimizes the glare for patients who are extremely bothered by glare

Aqueous humor

Transparent fluid occupying the anterior chamber and maintains eye pressure

Argon laser

device used to treat glaucoma (usually open angle) and diabetic retinopathy using a thermal beam

ARMD, age related macular degeneration

Destruction and loss of the photoreceptors in the macula region of the retina resulting in decreased central vision and, in advanced cases, blindness

Astigmatic Keratotomy (AK)

Treats astigmatism by flattening the cornea with arc-shaped incisions in its periphery, similar to RK

Automated Lamellar Keratoplasy (ALK)

Procedure that predates LASIK eye surgery and is not generally used any more

Automated perimeter

Computer-driven device used to plot defects in the visual field (peripheral vision or side vision). Usually, this is a large hemisphere shell into which the patient's head is placed. Various points of lights, sometimes of different sizes, intensities and colors are projected onto the screen. The patient then indicates whether the light is seen and the response is recorded. The computer then plots the effective visual thresholds within the targeted visual field

BCVA, Best corrected visual acuity

Best possible vision a person can achieve with corrective lenses, measured in terms of Snellen lines on an eye chart .

Beta-carotene

Member of the carotinoid family of vitamins, a precursor to vitamin A, thought to be beneficial to the eyes, helpful in treating diseases such as glaucoma.

Bifocals

Lenses containing two focal lengths, usually arranged with the focus for distance above and near focus below.

Binocular vision

Simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and parallax-induced depth perception.

Blepharitis

Inflamation of the eyelids, a common problem which tends to be reoccuring in nature.

Blind spot

The area of the optic disk where the optic nerve fibers exit the eye and where there are no light-sensitive cells. This small area can be measured and in glaucoma, as the nerve fibers die, the blind spot tends to enlarge and elongate. This is one of the diagnostic hallmarks of glaucoma.

Bowman's membrane

Extremely thin second layer of the cornea, situated between the epithelium and stroma, thought to be responsible for epithelium adhesion.

Capsular haze

A thin film of scar tissue that occasionally forms on the posterior capsule behind the intraocular lens implant following cataract surgery and removed with a Nd - Yag laser.

Caruncle

Small, red portion of the corner of the eye that contains modified sebaceous and sweat glands.

Cataract

Gradual clouding of the crystalline lens resulting in reduced vision or eventual blindness, correctable by cataract surgery.

Cataract surgery

Removal of a cataract, replacing it with an intraocular lens implant.

Central islands

Central islands are a small mound of central tissue, which can interfere with vision and occur when the laser beam does not uniformly remove tissue in the center of the treatment.

Choroid membrane

Dark, vascular, thin skin-like tissue, situated between the sclera and the retina, forming the middle coat of the eye. The choroid membrane nourishes the outer portions of the retina and absorbs excess light.

Chronic

Of long duration, going on for some time.

Closed angle glaucoma

Glaucoma conditions occurring suddenly (acute).

Ciliary body

Part of the eye that connects the choroid membrane to the iris. Produces aqueous humor that fills the front part of the eye and maintains eye pressure.

Ciliary muscle

Muscle attached to the crystalline lens responsible for focus (the same as ciliary body, but used in a different context).

Clear Lens Extraction (CLE)

Procedure in which the eye's natural clear crystalline lens is removed and replaced with an intraocular lens implant, using the same technique as cataract surgery.

Colorblindness

Inaccurate term for a lack of perceptual sensitivity to certain colors. Absolute color blindness is almost unknown.

Color vision

Ability to perceive differences in color, including hue, saturation and brightness.

Comprehensive eye exam

Evaluation of the complete visual system.

Conductive Keratoplasty (CK)

Procedure in which a radio frequency probe, rather than a laser, is used to reshape the cornea. It is approved for low to moderate hyperopia in patients over age 40, however it does not appear to have the precision of LASIK.

Cones

One of the two types of light-sensitive cells, concentrated in the center of the retina (also see rods ). There are about 6.5 million cones in each eye - 150,000 cones in every square millimeter - responsible for detailed visual acuity and the ability to see in color.

Conjunctiva

Mucous membrane lining the inner surface of the eyelids and covering the front part of the sclera (white part of eye), responsible for keeping the eye moist.

Conjunctivitis

Inflammation or irritation of the conjunctiva . Symptoms can be present in just one eye, or it can affect both eyes and include redness of the eyes or the edges of the eyelids, swelling of the eyelids or itching.

Contact lens

Small, thin removable plastic lens worn directly on the front of the eyeballs, usually used instead of ordinary eyeglasses for correction or protection of vision.

Convergence

Turning of the eyes inwards so that they are both "aimed" towards a nearobject being viewed. Normally works in harmony with divergence which is used for more distant objects.

Cornea

Transparent tissue that forms the front part of the eyeball, covering the iris and pupil. The cornea is the first part of the eye that bends (or refract s) the light and provides most of the focusing power.

Corneal curvature

Shape of the front of the eye.

Corneal mapping, topography

A tool used to see the refractive problems that might be present in the cornea. Corneal topography is used not only for screening all patients before refractive surgery like LASIK but also for fitting contacts.

Corneal relaxing incisions (CRIs)

True corneal incisions, such as RK and AK.

Corneal transplant (penetrating keratoplasty)

Surgical operation of grafting a replacement cornea onto an eye.

Crystalline lens

Double convex, transparent part of the eye, located behind the iris and in front of the vitreous body. Serves in conjunction with the cornea to refract incoming rays of light onto the retina.

Cylinder

Refers to the degree of astigmatism (uneven roundness) present in the cornea.

Depth perception

Ability of the vision system to perceive the relative positions of objects in the visual field

Detached retina

A retinal detachment occurs when the retina is pulled away from its normal position in the back of the eye.

Diabetes mellitus

Chronic metabolic disorder characterized by a lack of insulin secretion and/or increased cellular resistance to insulin, resulting in elevated blood levels of simple sugars (glucose) and including complications involving damage to the eyes, kidneys, nervous system and vascular system

Diabetes type I (IDDM)

Insulin dependent, resulting from destruction of the insulin producing pancreatic islet cells

Diabetes type II (NIDDM)

Non-insulin dependent, resulting from tissue resistance to insulin

Diabetic retinopathy

Deterioration of retina l blood vessels in diabetic patients, possibly leading to vision loss.

Dilated, dilation

Enlargment of the pupil (space in the middle of the iris)

Diopter

Unit of measure of the refractive power of an optical lens (equal to the power of a lens with a focal distance of one meter). A negative diopter value (such as -3D) signifies an eye with myopia and positive diopter value (such as +3D) signifies an eye with hyperopia .

Diplopia

Condition in which a single object is perceived as two; also called double vision.

Divergence

Turning of the eyes outwards so that they are both "aimed" towards the object being viewed. Normally works in harmony with convergence

Double vision

Same as diplopia

Dry eye

A common condition that occurs when the eyes do not produce enough tears to keep the eye moist and comfortable.

Emmetropia

Twenty-twenty vision.

Endothelium

Cellular tissue that covers the inner surface of the eye within the closed cavity, typically referring to the cornea .

Enhancement

An additional LASIK procedure, used in the refinement of Personal Best Vision

Epithelium

Cellular tissue that covers the outer surface of the eye. Consists of one or several layers of cells with only little intercellular material.

Esophoria

Position of the eyes in an over-converged position compensated by the external eye muscles so that the eyes do not appear turned inward.

Excimer laser

Laser used in LASIK surgery that operates in the ultraviolet wavelength, producing a cool beam.

Extracapsular cataract surgery

Surgery in which the cataract is removed in one piece through a larger incision, which usually requires several stitches.

Extraocular muscles

Six muscles that control eye movement. Five originate from the back of the orbit; the other one originates from the lower rim of the orbit. Four move the eye up, down, left and right, the other two control the twisting motion of the eye when the head tilts. All six muscles work in unison; when they do not function properly, the condition is called strabismus.

Eye chart

Technically called a Snellen chart, a printed visual acuity chart consisting of Snellen optotypes, which are specifically formed letters of the alphabet arranged in rows of decreasing letter size.

Eyelid

Either of two movable, protective, folds of flesh that cover and uncover the front of the eyeball.

Farsighted

Common term for hyperopia.

FDA

Abbreviation for the Food and Drug Administration. It is the United States governmental agency responsible for the evaluation and approval of medical devices.

Femtosecond laser

Used in the IntraLASIK procedure to make a safer and more precise flap than the older mechanical microkeratome technology, it uses a longer wavelength, smaller spot, and shorter duration per pulse than the excimer laser used to reshape the cornea.

Field of vision

Entire area which can be seen without shifting the gaze.

Flap

Part of the cornea consisting of epithelium , Bowman's membrane and some stroma , cut with a remaining hinge and lifted up as part of the LASIK procedure.

Flashes & floaters

Light spots or streaks and dark moving specks due to the vitreous traction on the retinal (light flashes) and solid vitreous material or blood (floaters).

Fluorescein angiography

Diagnostic test by which the veins deep inside the eye are examined. Dye is injected into a vein in the arm and circulated by the blood to the back of the eye, allowing for visual examination.

Fovea

Small depression in the retina , the point where vision is most acute.

Fundus

Furthest point at the back of the eye, consisting of the retina , choroid membrane , sclera , optic disc and blood vessels, seen by means of the ophthalmoscope.

Ghost image

Faint second image of the object you are viewing.

Giant papillary conjunctivitis

Type of conjunctivitis wherein bumps or ridges form on the inside of eyelids, which make wearing contact lenses uncomfortable; in fact, this condition is often caused by overwearing of certain contact lenses.

Glare

Scatter from bright light that decreases vision.

Glaucoma

Painless disease of the eye characterized by increased pressure within; left untreated it leads to a gradual impairment of sight often resulting in blindness.

Gonioscopy

Viewing procedure utilizing a mirror/lens device placed directly upon the cornea that is used to view the drainage area called "the angle" through which aqueous fluid exits the eyeball.

Halos

Rings around lights due to optical imperfections in, or in front of, the eye.

The arms of an intraocular lens , which holds it in place once inserted inside the eye.

Haze

Corneal clouding that causes the sensation of looking through smoke or fog.

Heterophoria

Constant tendency of one eye to deviate in one or another direction due to imperfect balance of ocular muscles.

Holmium laser

A laser which operates in the infrared wavelength, producing a hot beam. It is used in Laser Thermokeratoplasty surgery and more commonly in surgical procedures involving the disintegration of stones and fibrous tissue ablation .

Hyperopia

Also called farsightednesss, hyperopia is the inability to see near objects as clearly as distant objects, and the need for accommodation to see distant objects clearly.

Hypoxia

Deficiency of oxygen supply to a tissue.

Image

Light reflected into the eye, off objects in front of the eye. This light contains all the information about the objects (such as color, shadow. motion and detail) that are translated to the brain and allow you to "see" (know about the objects).

Inflammation

Body's reaction to trauma, infection, or a foreign substance, often associated with pain, heat, redness, swelling, and/or loss of function.

Informed Consent Form

Document disclosing the risks, benefits, and alternatives to a procedure.

In Situ

Term meaning "in place".

Intracapsular cataract surgery

Cataract surgery in which both the lens and capsule are completely removed, a rarely used procedure.

Intraocular lens implant (IOL)

Permanent, artificial lens surgically inserted inside the eye to replace the crystalline lens following cataract surgery or clear lens extraction.

Intraocular pressure (IOP)

Fluid pressure within the eye created by the continual production and drainage of aqueous fluid in the anterior chamber.

Iridotomy

Treatment for closed-angle glaucoma, one of the many types of glaucoma, usually done with a laser .

Iris

Colored part of the eye. Elastic, pigmented, muscular tissue in front of the crystalline lens that regulates the amount of light that enters the eye by adjusting the size of the pupil in the center.

Ischemia

Restriction or blockage of blood flow through a blood vessel. Ischemia is a causative agent of certain heart attacks and strokes and is involved in various types of visual field losses.

Intacs

Surgically implanted plastic half rings that change the shape of the cornea .

Keratectomy

Surgical removal of cornea l tissue.

Keratitis

Inflammation of the cornea.

Keratotomy

Surgical incision (cut) of the cornea .

Keratoconous

Rare, serious, degenerative cornea l disease, in which the cornea thins and assumes the shape of a cone.

Keratomileusis

Carving of the cornea to reshape it.

Keratoplasty

Surgical reshaping of the cornea

Lacrimal apparatus

Part of the eye that produces tears.

LASEK

Laser Epithelial Keratomileusis, a refractive surgery in which the epithelium is cut with a fine blade, called a trephine, and involves displacing the cornea l epithelium as a sheet and then replacing it to (theoretically) act as a natural bandage.

Laser

Device that generates an intense and highly concentrated beam of light. Acronym for – Light Amplification by Simulated Emission of Radiation. (Also see – holmium laser, argon laser, Nd – YAG laser, femtosecond laser, and excimer laser)

Laser Thermokeratoplasty (LTK)

Holmium 'hot' beam laser, instead of the 'cool' beam excimer laser, is used to treat farsighted patients and is very limited in its application; the effects are not long lasting.

LASIK

Laser Assisted In-Situ Keratomilieusis, a refractive surgery in which Excimer laser ablation is performed under a flap on the cornea to correct refractive errors .

Lazy eye

Amblyopia, an eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease.

Legally blind

20/200 vision and over is the qualification of legal blindness in the United States.

Lens

Same as the crystalline lens . Double convex, clear part of the eye, behind the iris and in front of the vitreous humor. Serves to refract the various rays of light so as to form an image on the retina .

Lenticular

Special non-cataract lenses for patients who have cataracts.

Lid speculum

A surgical tool that holds the eyelids open and which allows the surgeon to gain access to the eye with minimal pressure on the globe.

Limbal relaxing incisions (LRI)

Small incisions placed on the far peripheral aspect of the cornea resulting in a cornea that is more round, for correcting astigmatism.

Limbus

Thin area that connects the cornea and the sclera .

Low vision

Condition occurring when ordinary eyeglasses or contact lenses are unable to bring a patient's sight up to normal sharpness.

LTK (Laser Thermal Keratoplasty)

Holmium 'hot' beam laser, instead of the 'cool' beam excimer laser, is used to treat farsighted patients and is very limited in its application; the effects are not long lasting.

Lutein

Member of the carotinoid family of vitamins, similar to beta-carotene, thought to be beneficial to the eyes, helpful in treating diseases such as glaucoma.

Macula

Yellow spot on the retina, where the photoreceptors are most dense and responsible for the central vision. Has the greatest concentration of cones, responsible for visual acuity and the ability to see in color.

Macular edema

Collection of fluid in and under the macular portion of the retina .

Macular degeneration

Disease of the macula, which results in the loss of central vision.

Meridian

Orientation of a particular curve, often used in relation to the cornea .

Microkeratome

Mechanical surgical device that is affixed to the eye by use of a vacuum ring. When secured, a very sharp blade cuts a layer of the cornea at a predetermined depth.

Miosis

Pupillary constriction.

Monovision

Purposeful adjustment of one eye for near vision and the other eye for distance vision.

Mydriasis

Pupillary dilation.

Myopia

Also called nearsightedness or shortsightedness, the inability to see distant objects as clearly as near objects.

Near point of accommodation

Closest point in front of the eyes that an object may be clearly focused.

Near point of convergence

Maximum extent the two eyes can be turned inwards.

Nearsighted

Common term for myopia.

Neodymium YAG Laser

Laser used to treat Posterior Capsular Opacification (PCO) as well as open angle glaucoma Selective Laser Trabeculoplasty.

Neovascularization

Often associated with diabetes, involves the formation of new blood vessels, often fragile and inappropriate for the location.

Nerve fibers/axons

Extensions of photoreceptors that form the nerve bundle that is called the optic nerve.

Neuro-ophthalmology

Subspecialty that treats the nervous and vascular systems that involve the eye.