20/20 vision a term used to express normal visual acuity, the clarity or sharpness of vision, measured at a distance of 20 feet. Having 20/20 vision, means a patient can see clearly at 20 feet what should normally be seen at that distance. If a patient has 20/100 vision, it means that the patient must be as close as 20 feet to see what a person with normal vision can see at 100 feet. 20/20 vision does not mean perfect vision, only indicating the sharpness or clarity of vision at a distance. Also known as the standard for Snellen Acuity in the United States.

Ablate to remove an organ or body structure or tissue by surgery.

Ablation a general term for the excision of tissue during surgery, commonly used to describe the vaporization of tissue with the excimer laser.

Ablation zone the area of tissue that is removed during laser or other types of surgery.

Acuity a measurement of vision clarity or clearness. The most common measure of visual acuity is Snellen Acuity where completely normal acuity is expressed as 20/20. See 20/20 vision. Also known as clearness.

ACULAR® a tradename for the chemical ketorolac tromethamine. A nonsteroidal anti-inflammatory eyedrop used to reduce pain after laser vision correction procedure.

Amblyopia a condition in which the vision in the non-dominant eye is poor as a result of a visual abnormality early in life. Also know as cycloplegic and lazy eye.

Ametropia the refractive condition where parallel rays do not focus on the retina that is, there is an imperfection in the refractive state of the eye.

Aniseikonia a condition where there is a difference in imaging size between the two eyes.

Anisometropia a condition where there is a difference in refractive power of the two eyes in which the variance is at least one diopter.

Anterior Chamber a fluid-filled area of the eye between the cornea and the lens. The fluid is known as aqueous humor.

Aqueous Humor the fluid in the anterior chamber. See anterior chamber.

Argon Laser a device that produces laser light from argon gas. The main wavelengths are 488.0 nm blue and 514.5 nm pea green light, but nine separate wavelengths in the blue-green visible light spectrum are produced. Many of the lasers used in laser eye surgery are argon lasers.

Array Multifocal Intraocular Lens a lens implant used in cataract surgery that provides clear vision both near and far. This is accomplished by structure of the surface of the lens, which contains concentric rings of varying power around a central power for distance. The rings of power are for the near distances, while the central distance power is "dominant." Thus, there is little if any loss or sacrifice of distance vision to obtain near vision. 50% of the lens is dedicated to distance vision, 36% to near vision, and 14% to intermediate ranges.

Asphericity the natural optical shape of the cornea. This shape determines the number of light rays falling on the retina and the sharpness of image under all types of lighting conditions. When this shape is altered, there can be optical aberrations such as glare or shadows.

Astigmatic Keratotomy a surgical procedure in which microscopic incisions are placed in the peripheral cornea to create a more spherical shape. This technique has largely been replaced by more advanced laser vision correction techniques. Also known as AK.

Astigmatism a condition in which the surface of the cornea is elliptical rather than spherical. Causes a blurred image to be received at the retina. Refractive correction includes a lens that has focusing power in one axis and no power in the opposite axis. Astigmatism is often expressed in the second number of lens prescriptions and is measured in diopters.

Automated Lamellar Keratoplasty a surgical procedure utilizing a micro planing device to remove a microscopic section of corneal tissue. Used to correct large amounts of myopia and mild to moderate amounts of hyperopia. This procedure has been replaced by the significantly more accurate laser vision correction techniques. Also known as ALK.

Axis a line passing through the center of curvature of an optical surface. The axis defines the surface's symmetrical center.

Best-corrected Spectacle Visual Acuity (BCVA) the best clearness or sharpness that can be achieved through lens correction. Often used to describe the refractive condition of an eye after laser surgery. If the vision can't be corrected to its preoperative visual acuity with lenses then there may be an irregular corneal surface (irregular astigmatism). If so, a hard contact lens may be necessary to get the best visual acuity.

Bifocal a lens having one segment for near vision and one segment for far vision.

Binocular of or relating to both eyes.

Bowman's Membrane the non-regenerative layer of tissue between the epithelial and the stromal layers of the cornea. This layer is not affected by LASIK but is during a PRK procedure.

Broad Beam Laser a medical instrument that produces a powerful beam of light that is focused at close range to remove corneal tissue. A broad beam laser uses a relatively large beam diameter (from 6.0 to 8.0 millimeters) which can be manipulated to ablate the cornea.

CRSQA acronym for The Council for Refractive Surgery Quality Assurance. The council is an independent, nonprofit, patient/consumer health organization that evaluates, monitors, and verifies the quality of the surgeries provided by select refractive surgeons in the United States.

Cataract a cloudiness or opacity of the normally clear lens of the eye. There are many causes of cataracts, including aging, cortisone medication, trauma, diabetes, and other diseases. Treatments can include surgical implantation of a new lens. See cataract surgery.

Capsulotomy the surgical removal of a capsule, or residual tissue from cataract surgery. See YAG laser.

Cataract surgery removal of the clouded (cataractous)lens in its entirety by surgery, and replacement of the lens with an intraocular lens (IOL) made of plastic. The typical cataract operation takes about an hour, requires local anesthesia only, and usually does not need hospitalization. See intraocular lens.

CE Mark when displayed, this mark indicates a medical device fulfills requirements for sale in the 15-nation European Union.

Central Island a complication of laser vision correction where the laser beam fails to remove a portion of cornea, usually in the center of the area to be removed. If the concave area of the ablation is a lake this complication is an island of tissue sticking up in the center. Visual symptoms include monocular double vision or distortion.

Central Optical Zone the center area of the cornea, critical clear vision. Incisions in RK procedure are made around this zone.

Concave Lens a type of lens with a hollow shape like the inside surface of a ball. A lens of this type diverges the light rays that will be entering the eye, moving the true focal point of the light to a point in front of the lens. This effect corrects the refractive defect in the nearsighted eye. Concave lenses are minus power lenses.

Confrontation Visual Fields a test of peripheral vision. It is performed to identify vision defects that may indicate disease, such as glaucoma.

Conjunctiva a delicate mucous membrane that lines the eyelids and covers the white surface of the eye. The conjunctiva joins the eyeball at the edge of the cornea, called the limbus.

Contrast Sensitivity a method of testing overall vision quality varying the illumination and size of the object being viewed. This is considered a more comprehensive test than the standard Snellen test.

Convex Lens a lens with a bulging surface like the outer surface of a ball. A lens of this shape collects the light rays that will be entering the eye and reduces the distance to the focal point. Convex lenses are positive power lenses and are used to correct hyperopia or far sightedness and for reading glasses, as needed to correct presbyopia.

Cornea the transparent front structure of the eye that covers the iris. The cornea has 5 layers: the corneal epithelium, Bowman's Membrane, the corneal stroma, Descemet's Membrane, and the corneal endothelium. Refractive procedures, such as LASIK involve changing the shape of the cornea.

Corneal Curvature the shape of the cornea measured in diopters or millimeters of curvature. This characteristic is responsible for 70% of the eyes focusing power.

Corneal Endothelium the innermost layer of cells of the cornea. The endothelium serves three main purposes in the eye: regulation of the water content of the stroma, providing a barrier to ingress of several constituents of the aqueous humor, and actively transporting glucose, the fuel used by cells.

Corneal Epithelium the outermost layer cells of the cornea. The epithelium is the eye's first defense against infection.

Corneal Haze a complication of refractive surgery characterized a cloudiness of the normally clear cornea. This complication sometimes occurs after PRK and but rarely after LASIK. Any build up of inflammatory infiltrates (white blood cells), extra moisture, scar tissue, or foreign substances (like drugs) can cause a clouding of the cornea. Most types of haze will disappear with time or drug treatment but it can be sometimes permanent.

Corneal Periphery the area of the cornea outside the central optical zone. See central optical zone.

Corneal Stroma the thickest layer of the cornea, it lies between the Bowman's membrane and Descemet's membrane.

Corneal Topographer a device used to measure and evaluate the corneal curvature of the eye. Lines and circles within the machine are used to observe the corneal reflex. This device also includes a means of recording corneal curvature by taking photographs of the cornea. Also known as a keratoscope or photokeratoscope.

Corneal Topographical Map a record of the surface profile of the cornea produced by a corneal topographer or keratoscope.

Corneal Topography a quantitative measurement of corneal curvature. The process is performed using a unique camera/computer combination called a corneal topographer or keratoscope. Used to determine corneal slope and astigmatism for laser vision - refractive correction. Also used post-operatively to measure the results of laser vision - refractive treatment. The computer data can manipulated to show the efficacy of ablation and the quality of smoothness of the final refracted surface. See corneal topographer.

Cover Test the test that is used to determine whether a patient has strabismus, or abnormal alignment. The test measures the movement of each eye independently to visual stimuli to detect abnormal reactions, indicating the eyes will not work well together. See strabismus.

Cycloplegic Refraction the true lens prescription of an eye measured when focusing ability of the eye has been inactivated through the administration of a chemical.

Cylinder meridian in ophthalmology, a line that is the symmetrical center of a curved optical surface. Also a measure of astigmatism.

Decentration a complication of laser eye surgery caused by movement of the pupil during the surgical procedure. The condition can often be corrected with an enhancement procedure. In perfect centration the center of the corneal ablation exactly coincides with the center of the visual axis and/or pupil. This condition is caused when the ablation area is not perfectly centered. Decentration can cause various symptoms including edge glare or even monocular double vision.

Descemet's membrane the layer of the cornea between the stroma and endothelium. This membrane provides an adhesion layer for the endothelium.

Deturgescence the balance of hydration in the eye.

Dilated Fundus Examination an examination of retinal tissue health in the back of the eyes. See dilation.

Dilation a process, when performed on the pupil of the eye, which allows visualization of the anatomic structures behind the iris in the back of the eye. Doctors use mydriatics, pharmaceutical drops that act upon the muscles of the iris, to enlarge the pupil diameter.

Diopter a unit of measurement for optical lenses. The number of diopters indicates the quantitative change in the distance between the lens and the focal point of light rays entering the lens. A positive diopter value describes a convex lens, while a negative value describes a concave lens. This differentiation describes the focal point of light entering a convex lens as being beyond the lens, while the focal point of light entering a concave lens as being in front of the lens. See convex lens, concave lens.

Diplopia a condition characterized by seeing multiple images. If the effect is with both eyes it is called binocular diplopia, but if occurring in only one eye it is monocular diplopia.

Dry eye a syndrome characterized by corneal dryness due to deficient tear production.

Ectasia a condition that can be a complication of laser eye surgery involving a progressive corneal thinning and bulging. Indications of this complication include a loss of the corrected vision in the eye.

Emmetrope a patient who exhibits no refractive error.

Emmetropia having perfect distance vision without the need of lens correction. The ophthalmic term for a normal eye in which light rays focus correctly on the retina, that is, there is no nearsightedness, farsightedness or astigmatism.

Endo- a prefix meaning within or inside.

Endophthalmitis an inflammation within the eye. Inflammations may be caused by organisms such as bacteria or may be sterile as in immune disorders. Endophthamistis is a term indicating a condition of having an infectious disease of the eye and is occasionally a complication of eye surgery.

Endothelium a general term for a layer of cells that lines an internal body surface or cavity. See corneal endothelium.

Enhancement a term for additional laser treatments made to refine or improve the original visual result. Because enhancement treatment usually a small correction these procedures traditionally have a highly accurate outcome. See regression.

Epiphora a condition characterized by having one or more watery eyes. The tears accumulate in the eye and trickle over the cheek.

Epithelial Ingrowth a complication of LASIK surgery wherein epithelial cells grow underneath the corneal flap. This can be treated by lifting the flap and removing the new growth.

Epithelium a general term for a layer of cells covering the external surfaces of the body. See corneal epithelium.

Excimer Laser an argon-fluoride laser that emits ultra-violet light at a wave length of 193 nm. This cool laser uses ultra-violet light to alter the front surface of the eye by breaking intramolecular bonds in collagen molecules during vision correction surgery.

Farsighted see hyperopia or hypermetropia.

Flap & Zap slang term for LASIK.

FLAREX® a tradename for a fluoromethalone acetate 0.1% solution. This corticosteroid eyedrop is used to reduce corneal haze and regulate healing response after a laser vision correction procedure.

FML® a tradename for a fluoromethalone .1% solution. This corticosteroid eyedrop used to reduce corneal haze and regulate healing response after a laser vision correction procedure. Also available in a 0.25% solution and called FML FORTE®.

Focusing Power the ability of the eye to focus light on the retina. About two thirds of the focusing power of the eye comes from the cornea, the rest comes from the lens inside the eye. As the light enters the eye it is focused a fixed amount by the cornea. As the light passes through the pupil the lens then adjusts the focus a variable amount. The exact amount of focusing power applied by the lens depends on the distance of the object being viewed. Laser vision correction adjusts the power of the eye by changing the focusing power of the cornea.

Ghosting a complication of refractive surgery involving a distortion of the visual image due to irregular healing of the corneal surface.

Glare a complication of refractive surgery in which the patient sees additional luster around lights. Glare is a subjective experience that often decreases with time.

Glare Testing a method of measuring visual performance by determining visual acuity with a simulated back-lit target. If general visual acuity is significantly reduced on glare testing, it may be because of an irregular corneal surface, corneal scar, or cataract.

Globe a common term for the eyeball.

Halos a complication of refractive surgery in which the patient sees additional rings around lights at night. Halos are subjective experiences that often decrease with time.

Haze a relatively rare complication of LASIK caused by the deposition of ground substance in the cornea. A slit lamp can be used to measure the haze response of a patient's eye. Haze results in decreased night vision, halos or loss of best corrected visual acuity.

Hyperope a patient who has difficulty seeing near objects because of the shape of the eye.

Hyperopia a refractive abnormality of the eye requiring a plus (positive or convex) lens for correction. Far or distance sighted people can see at a distance more clearly than they can see objects which are closer. The hyperopic eye is often described as being too flat or too short, as images are focused in back of the retina. The condition is corrected using a positive or convex lens. Also known as farsighted, hypermetropia. See convex lens.

Immune in medicine, protected against a disease.

Immune System a complex network of specialized cells and organs that has evolved to defend the body against attacks by invaders foreign to the body such as bacteria and viruses. A malfunction of the immune system where the body's own defenses attack itself is an autoimmune condition or disease.

INFLAMASE® a tradename for a prednisolone sodium phosphate solution. This corticosteroid eyedrop is used to reduce corneal haze and regulate healing response after a laser vision correction procedure. Available in forte (1.0%) and mild (1/8%) formulations.

Inflammation a protective tissue reaction to trauma often with pain, heat, redness, swelling, and/or loss of function. Inflammation may be caused by mechanical trauma, infections by bacteria or viruses, by immune reactions, and other causes.

INTACTS® a tradename for micro-thin, semi-circular plastic ring segments, that when implanted into the periphery of the cornea, cause the cornea to flatten allowing for the correction of mild near-sightedness. Also known as the ICRS®, or Intrastromal Corneal Ring Segments.

Intraocular Pressure the pressure the fluid contained within the eye exerts on the globe.

Iris the circular colored membrane behind the cornea, perforated by the pupil. The muscles of the iris regulates the amount of light admitted into the eye by opening and closing the pupil.

Irregular Astigmatism a refractive error caused by an irregular shape of the cornea in which the curve on one side of the meridian or axis is not symmetrical with the curve on the other side.

Keratectomy a surgical procedure involving the excision or removal of any portion of the cornea. In a penetrating keratectomy (or PK) a button-like full thickness segment of the cornea is removed and replaced with a donor cornea from another person. Also the term is used to describe the preliminary portion of the LASIK procedure in which the surgeon raises a thin layer of the cornea - creates a corneal flap - with an instrument called a microkeratome, to expose the layer of the cornea called the stroma.

Keratitis an inflammation of the cornea. Inflammation may be caused by trauma as in an abrasion, RK, or PRK; by infections by bacteria or viruses; or by immune disorders.

Kerato- a prefix indicating relationship to the cornea.

Keratoconjuntivitis an inflammation, infectious or auto-immune, of the cornea and conjunctiva.

Keratoconus an abnormality of the eye where the cornea becomes deformed in the shape of a cone. This condition is a contraindication to (or strong reason against having) refractive surgery.

Keratometry the measurement of corneal refractive power or curvature. The results are expressed in diopters (refractive power) or in millimeters of radius.

Keratomileusis a refractive surgical technique where a partial thickness circular flap of cornea is removed, frozen, lathed to a new shape and replaced upon the cornea. The lathe can shape either a convex or concave lens.

Keratoplasty the replacement (transplantation) of the cornea. Keratoplasty can be lamellar, involving replacement of superficial layers only or penetrating, replacement of the full thickness of the cornea.

Keratotomy a surgical incision of the cornea as in radial keratotomy, involving radially or clock hour aligned incisions in the cornea.

Lamellar keratoplasty The replacement of superficial layers of the cornea with the layers of another donor cornea.

Laser acronym for Light Amplification by the Stimulated Emission of Radiation. It is a device capable of producing single wavelength light where all waves are in the same phase. This light is capable of producing intense heat and power when focused at a close range. It is used in surgical procedures such as LASIK.

Laser Assisted In-Situ Keratomileusis an advanced laser procedure combining ALK and PRK to flatten or steepen the central cornea, thereby decreasing or eliminating myopia, hyperopia, and astigmatism. This procedure involves making a thin flap on the surface of the cornea. This flap is then lifted and folded to the side, and the underneath exposed surface is reshaped using the excimer laser. After altering the corneal curvature, the flap is replaced and adheres without stitches. Also known as LASIK.

Lens a transparent structure that focuses light rays which pass through it. The human lens is located behind the iris and combines with the cornea to provide the focusing power for the eye. See focusing power, cornea.

Leucoma a dense, white, opaque scar of the cornea.

Limbus the visible borderline between the cornea and the white globe, or sclera, of the eye.

Manifest Refraction The lens prescription that best corrects the vision of an eye.

Mask a structure used in laser vision correction surgery to modify the light beam produced to refine the removal of surface tissue by the laser. Some machines use an internal constricting diaphragm as an internal mask, especially for treatment of myopia. Variable rotation of the masks is used to deal with astigmatism. Others use external masks made of metal, especially for the treatment of hyperopia. A third type of mask is applied onto the cornea and is destroyed or ablated by the laser light during treatment.

Meibomian Secretion Oily secretion from the eyelid glands that supply the outer portion of tear film, prevents rapid tear evaporation and tear overflow.

Microkeratome an automated device used to create a flap on the cornea during the LASIK or ALK procedure.

Micron a metric unit of length equal to one millionth of a meter. Also known as micrometer.

Monovision the purposeful adjustment of one eye for near vision and the other for distance vision accomplished with either corrective lenses or surgery. This technique can be used to treat the effects of presbyopia.

Myope a patient who has difficulty seeing far objects because of the shape of the eye.

Myopia a refractive abnormality of the eye requiring a negative or concave lens for correction. A myopic eye has excess focusing power causing light rays to focus in front of the retina. Myopia causes blurred distance vision. Also known as nearsighted.

N.S.A.I.D. abbreviation for nonsteroidal anti-inflammatory drug. These drugs are most useful in alleviating pain from inflammatory conditions, though they do not modify the inflammatory process. One example is ibuprofen.

Nanometer a metric unit of length equal to one billionth of a meter. Also known as millimicron.

Nearsighted see myopia.

Nebulas a slightly opaque scar of the cornea.

Nomogram a surgeon's adjustment to the laser's computer calculation using a graphic representation of numerical results of prior procedures.

OCUFEN® tradename for a flurbiprofen sodium 0.03% solution. Nonsteroidal anti-inflammatory eyedrop used to reduce pain after vision correction procedure.

Off Label Use The permissible use of an approved drug or instrument in a way that has not been specifically sanctioned. The use of the excimer laser for LASIK surgery is an example of an off label use.

Ophthalmic pertaining to the eye.

Ophthalmologist a medical doctor who specializes in the eye. To become an Ophthalmologist one must first obtain a medical degree and then complete further specialty training. The specialist certification requires an extra 3 years in the USA or 4 years in Canada. Ophthalmology is technically a surgical discipline. Some ophthalmologists chose not to perform surgery and can be called medical ophthalmologists.

Optic nerve a collective name for the millions of nerve fibers connecting the eye to the brain where the images are created and processed.

Optician an expert in the art and science of making and fitting glasses. Various certifications optional but not mandated.

Overcorrection a complication of laser vision correction where the expected amount of correction is more than desired.

PMMA acronym for polymethylmethacrylate. A clear polymer used in Intacs®. Used since 1952 in intraocular lenses related to cataract surgery. See Intacs®.

Phoropter an optical instrument using a selectable series of intricate lenses that the patient looks through until maximum clarity is obtained, thus arriving at the patient's precise prescription.

Photoablation the cold process of tissue removal which occurs with laser radiation in the 200nm wavelength range. This far-UV wavelength possess light photons so powerful that the molecular bonds of the target tissue both break down and have sufficient extra kinetic energy to fly off the surface; hence ablation.

Photocoagulation

the process of tissue destruction accomplished by visible light radiation. Tissue is broken down by the light and clots as if it were cooked.

Photorefractive Keratectomy a surgical procedure utilizing an excimer laser to reshape the central cornea to a flatter shape for people who are nearsighted and a more curved surface for people who are farsighted. PRK techniques can also be used to correct astigmatism. Also known PRK.

Pinguecula a yellowish spot seen on the white of the eye at the junction of the clear cornea and white sclera of the eye. These lesions are usually caused by UV radiation. The white surface of the eye cannot tan and therefore cannot protect itself from the sun.

Plano characterized by no refractive error.

Practice of Medicine A regulatory body's allowance of practitioners to make decisions to best serve their patients

PRED® prednisolone acetate 1% Corticosteroid eyedrop used to reduce corneal haze and regulate healing response after a laser vision correction procedure. Available in forte (1%) and mild (.12%) formulations.

Presbyopia the natural deterioration of near vision as one ages. One theory is that this change is due to a progressive inflexibility of the eye's lens. A second theory is that the lens has grown to the point that the eye's focusing muscles can no longer contract enough to thin the lens for clear close vision. This condition can be corrected with bifocals, if the patient is myopic or hyperopic or reading glasses, if there are no other refractive abnormalities.

Phototherapeutic Keratectomy Cold laser removal of surface tissue of the cornea such as scar tissue for medical or optical treatment reasons.

Ptosis a condition characterized by a droopy eyelid.

Ptygeria a growth of scar tissue on the cornea. These lesions are caused by an ultraviolet burn to the surface layer or epithelium.

Pupil the small black circular opening in the center of the iris, the colored part of the eye. The pupil changes its diameter in response to changes in ambient lighting. Operating much like the aperture of a camera, the pupil varies the amount of light reaching the retina and the depth of focus of the eye.

Pupil Size in Dim Illumination one determinants for the level of glare symptoms after LASIK. If the pupil dilates in the dark to a size that is larger than the treatment zone of the laser, there is a risk of glare in the dark. Therefore it is important to have the size of the pupil tested prior to surgery.

Radial pertaining to the radius or line from a circle center to the circle itself.

Radial Keratotomy (RK) a surgical procedure which permanently alters the shape of the cornea by placing microscopically thin relaxing incisions in the peripheral cornea. This surgical operation makes incisional cuts approximately 90% in to the thickness of the cornea. These cuts are made in a radial fashion and spare the visual center of the cornea. The intention is to flatten the central cornea. This causes the central portion of the cornea to flatten reducing the power of the eye and correcting myopia. This technique has largely been replaced by newer laser vision correction techniques. Also known as RK.

Refraction Test an eye test that measures a person's ability to see an object at a specific distance. It is a measurement of focusing power of the eye. The test is performed using a photopter or a refractor.

Refractive Error when the eye does not provide the correct amount of focusing power for the axial length. When the eye provides too much power the person is nearsighted or myopic. When the eye does not provide enough power then the person is farsighted or hyperopic.

Refractive surgery any surgical procedure that attempts to decrease the patient's refractive error. Typically the surgeon alters the shape of the cornea in order to change the angle at which an image is projected onto the retina.

Regression a return to the original refractive state. During healing after laser surgery both the surface epithelium and the deeper corneal stroma can reshape and reform at different rates. Computer generated laser vision correction treatments assume a normal bell curve amount of healing for both layers and thus normally overcorrect the refractive error in order to finally heal with no refractive error and no need for glasses. A small percentage of patients will heal faster and more vigorously than expected and will thus regress or heal their planned over correction back past no refractive error to their original type of error. This regression phenomenon occurs with both myopic and hyperopic corrections.

Regular astigmatism a refractive error caused by an irregular shape of the cornea (usually a football shape) in which the curvature is symmetrical across one or more meridians or axes.

Retina the inner back surface of the eye. This tissue lines the inside of the eye similar to a piece of cellophane inside a hollow racquetball. This tissue converts light energy into nervous impulses and sends them to the part of the brain responsible for interpreting these impulses into images.

Retreatment see enhancement.

Slit lamp Table-top microscope for examining the eye used in a slit lamp examination to microscopically evaluate the health of the eye.

Snellen chart an eye chart used to test a patient's vision made up of Snellen lines, which are lines of same-sized alphabetic letters (or objects for pre-reading patients).

Snellen Test a test that measures quantity of vision, or acuity, in a high contrast format using numerous lines of same sized objects with the size of the objects as compared to the next line below it getting progressively larger.

Spot Scanning Laser A medical instrument that produces a powerful beam of light that is focused at close range to remove corneal tissue. Spot scanning lasers use radar technology to track the eye's movement.

steroid A large class of pharmaceutical agents that chemically resemble cholesterol. Two better known types are anabolic steroids as used illegally in athletics, and glucocorticoid steroids which are used to reduce inflammation. This latter drug type is used in PRK to regulate regression and reduce post PRK inflammatory haze.

Strabismus an abnormal alignment of the eye in any field of gaze, constant or intermittent, and occurring at distant and/or near fixation. Occurs mainly in early childhood and results from poor muscle coordination between the eyes. Detected using a cover test. When examining the affected eye, to not be focusing at the target object when, in fact, it is. The condition can affect a patient's candidacy for LASIK. Less than 5% of the population have strabismus. Also called lazy eye. See cover test.

Stroma A general term for supporting or central tissue of the body. See corneal stroma.

Symmetry of Refractive Error when the refractive error in both eyes are close to the same value.

Tear film a very thin film of water and other chemicals riding on top of the epithelium that lubricates the front of the eye.

The Council for Refractive Surgery Quality Assurance See CRSQA.

Tonometry the measurement of intraocular pressure.

Topical proparacain hydrochloride an anaesthetic eye drop.

topography an accurate and detailed description or drawing of places or items and their surface details. Used to determine the corneal profile in order to program the laser vision correction computer for refractive correction as well as for post-operative corneal analysis. See corneal topography.

Trifocal a lens design that has three focal areas: a lens for close work or reading, a lens for mid-distance viewing or arm's length, and a lens for faraway viewing or driving.

Uncorrected visual acuity a person's vision without corrective lenses measured in terms of Snellen lines on an eye chart. Also known as UCVA.

Undercorrection the result achieved when desired change in refractive error is not fully achieved. A result of laser vision correction treatment where the expected amount of correction is less than desired. See regression.

Vision Correction Surgery A general term for a surgical technique that aims to correct refractive abnormalities of the eye. Techniques include radial keratotomy (RK), photorefractive keratectomy (PRK), laser-assisted intrastromal keratoplasty (LASIK), and automated lamellar keratoplasty (ALK), insertion of intra-stromal corneal rings (ICRS), intra-ocular corrective lens (IOCL), or any other refractive procedure. Also known as refractive surgery.

Visual Acuity See acuity.

Vitreous Humor the gel-like fluid in the main cavity of the eye behind lens and pupil.

VOLTAREN OPHTHA® a tradename for a 0.1% solution of diclofenac sodium. This nonsteroidal anti-inflammatory eyedrop is used to reduce pain after laser vision correction procedure.

wavelength The distance between the top of one wave and the top of the next wave. The argon fluoride excimer wavelength is 193 nm. This wavelength is in the far ultraviolet end of the electromagnetic spectrum.

YAG laser a type of laser using an infra red wavelength of 1064 nanometers. The laser material is neodymium Yttrium-Aluminum-Garnet. YAG lasers are used after cataract surgery to photovaporize the residual membrane behind the artificial lens. The common misconception that lasers are used to remove cataracts occurs because about 75% of post-cataract patients eventually require YAG laser capsulotomy.