Dr. Robert Maloney believes that a well-informed patient is key to successful vision correction surgery. He wants to be sure that you fully understand what you can expect from your procedure you choose. He wants to help you care for and preserve your eyesight in the best way possible. Here, you can find the information that you need to help you make informed choices about health care for your eyes.

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20/20 vision: Normal visual acuity. The numbers indicate that the tested eye, twenty feet away from the eye chart, sees as well as a “normal” eye at the same distance.

Ablate: To remove, or vaporize, tissue, using laser energy.

Ablation: Removal, or vaporization, of tissue with a laser.

Ablation zone: The area of tissue removed by the laser. Also called the treatment zone.

Accommodating intraocular lens: A type of intraocular lens (IOL) that enables the patient to focus at a range of distances in much the same way as with a clear, flexible natural lens.

Accommodation: The eye’s ability to change lens shape (by action of the ciliary muscle and zonules) in order to focus clearly on objects at various distances. As the lens becomes more rigid with age—a condition called presbyopia—it is less able to accommodate.

Aftercataract: Opacity that develops on the posterior lens capsule after extracapsular cataract removal.

All laser LASIK: This term has been used to describe both the Intralase microkeratome and PRK.

Amblyopia: Poor vision, usually in one eye but occasionally in both eyes, that develops between birth and age six. Caused by continued suppression of vision in the affected eye, not by structural abnormality.

Amsler grid: Grid consisting of lines on contrasting background (black on white or white on black) used to test for macular degeneration or other central-visual-field defects.

Anterior chamber: Area between the cornea and the iris filled with aqueous humor.

Anterior ciliary sclerotomy (ACS): A surgical procedure intended to relieve presbyopia. Several small incisions are made in the sclera (white part of the eye) directly over the muscle that controls the lens. The results of the procedure are poor, and very few doctors perform it.

Antibiotic drops: Eyedrops containing medicine that prevents infection by killing or inhibiting harmful bacteria.

Anti-inflammatory drops: Eyedrops containing medicine that counteracts inflammation, usually a steroid or a nonsteroidal medicine similar to ibuprofen.

Aphakia: Absence of the crystalline lens of the eye.

Aqueous humor: Clear, watery fluid that fills the anterior chamber of the eye; maintains intraocular pressure and nourishes the cornea, iris, and lens.

Artificial tears: Sterile eyedrops used to lubricate the eyes the same way natural tears do.

A-scan: Ultrasound device used to distinguish normal from abnormal eye tissue or to measure eye length.

Aspheric intraocular lens: A type of IOL that is slightly flattened around the edges; believed to offer better contrast sensitivity than traditional IOLs, on which the front surface is curved.

Astigmatism: Visual distortion caused by a cornea whose surface is elongated—like the side of a football—rather than curved like an arc on a sphere. Light rays enter the eye unequally and may produce two focal points on the retina.

Astigmatism management: A surgical procedure designed to prevent or minimize worsening of astigmatism, a common side effect of refractive lens exchange.

Automated lamellar keratoplasty (ALK): An older refractive surgery, developed in 1987, in which the surgeon first creates an extremely thin flap in the uppermost layer of the cornea, using a device called a microkeratome, and then makes a second pass with the microkeratome to remove additional tissue. It is not performed anymore.

Autorefractor: A device, used to test refractive error, that emits a pinpoint beam of light, which reflects off the retina and measures the eye’s response.

Axis: A measurement of the direction of astigmatism. The astigmatic cornea is oval in shape, and axis is the angle of the long direction of the oval with a horizontal line.

Benchmarking: The process of tracking statistical outcomes for the purpose of predicting future outcomes. With LASIK, statistics from 1,000 or more procedures can provide a good basis for benchmarking.

Best corrected vision: The best possible vision achieved with corrective eyeglass lenses.

Best corrected visual acuity (BCVA): The best vision possible with corrective lenses.

Biomicroscope: See slit lamp.

Blended vision: See monovision

Blind spot: Sightless area within normal visual field; caused by absence or blockage of light-sensitive photoreceptors on the retina (specifically the fovea)

Blunt cannula: A narrow tube with a blunted tip, designed to perform many of the piercing functions of a surgical needle but without the needle stick.

Board certified: A credential awarded to physicians who have undergone the additional training and proved proficiency in an area by passing a rigorous examination. Ninety percent of ophthalmologists are board certified, so this credential is of limited value in distinguishing one ophthalmologist from another. If a surgeon is not board certified in ophthalmology, beware!

Brunescence: Browning of the crystalline lens due to cataracts.

Capsular bag: A thin membrane that forms the outermost layer of the crystalline lens, above the cortex and the nucleus.

Capsule: See capsular bag

Cataract: Clouded area (opacity) of the crystalline lens; caused by trauma, disease, or aging, or may be congenital.

Central island: A treatable complication from LASIK in which a small, raised area in the center of the cornea’s treatment zone results from its having received less laser energy than the surrounding tissue. Central islands can cause distorted vision.

Central vision: In the visual field, the area of sharpest vision, used for reading and distinguishing detail and color. See also peripheral vision.

Choroid: Layer of blood vessels that provide oxygen and nutrients to the retina.

Ciliary body: Eye structure that contains ciliary muscle, which contracts or relaxes, thereby changing the shape of the crystalline lens and allowing it to focus on objects at varying distances.

Ciliary muscle: See ciliary body.

Clear-corneal phacoemulsification: An advanced type of cataract surgery in which the incision is placed at the edge of the clear cornea. Clear-corneal phacoemulsification does not require the use of needles, does not cause bleeding, uses a very small (one-eighth of an inch or smaller) incision, and allows for rapid recovery.

Color blindness: Inability to clearly distinguish certain colors. Socalled red-green color blindness is usually hereditary. Yellowing of cataracts can also cause a degree of color blindness.

Comanagement: An arrangement in which the surgeon does the surgery and the primary eye doctor does all or part of the preoperative or postoperative care. Ideally, comanagement offers the advantage of a second expert to oversee care and ensure the patient’s satisfaction with the results.

Cone: One of more than 7 million retinal photoreceptor cells (in each eye) concentrated in the macular area (specifically the fovea centralis) of the retina, responsible for sharp vision and ability to see colors.

Congenital cataract: A cataract that is present at birth.

Conjunctiva: Clear mucous membrane that covers the white of the eye (sclera) and lines the inner surface of the eyelids.

Contrast sensitivity: Ability to visually distinguish dark objects against a light-colored background, or light-colored objects against a dark background.

Cornea: The outer, dome-shaped, transparent part of the eye that bulges out at the front of the eyeball and covers the iris and pupil. Its curvature causes light to bend. The cornea provides most of the eye’s focusing power. It is the only part of the eye on which LASIK is performed.

Corneal edema: Abnormal fluid buildup and consequent swelling of the cornea.

Corneal pachymetry: Measurement of corneal thickness using ultrasound.

Corneal topographer: An instrument that creates a three-dimensional map of the cornea, using computerized analysis.

Corneal topography: Rendering of a precise three-dimensional map of the cornea using sophisticated camera and computer technology.

Cortex: Soft, clear tissue that forms the middle layer of the crystalline lens between the capsule and the nucleus.

Cortical cataract: A cataract that begins as whitish, wedge-shaped opaque areas on the outer edge of the lens cortex, near the capsule, eventually becoming streaks reaching inward to the center of the lens, like spokes on a wheel.

Cryolathe: A mechanical lathe used to grind a frozen corneal disc into a new shape before it is replaced on the eye.

Crystalline lens: The eye’s natural lens; a flexible, transparent tissue, located behind the iris, that helps focus rays of light onto the retina. See also lens.

Cylinder: One of three measures in an eyeglass prescription. It indicates whether astigmatism is present, and to what degree.

Cystoid macular edema: A condition in which fluid-filled cysts develop in the macula, causing retinal swelling.

Diabetes mellitus: A group of diseases that develop when the body is unable to use blood sugar for energy, causing excessive amounts of sugar in the bloodstream (hyperglycemia).

Diffuse lamellar keratitis (DLK): A potential complication of LASIK; also known as “sands of the Sahara” syndrome. DLK is a noninfectious inflammation that arises between the corneal flap and the underlying stroma.

Dilation: Enlargement (of an opening). With reference to the eye, dilation of the pupil occurs naturally in dim light, allowing more of the available light into the eye. Eye doctors also chemically dilate the pupil during an eye examination in order to have a better view into the interior of the eye.

Diopter: A measurement of how strong a lens is. Thicker lenses have a higher number of diopters. In eye care, it is used to measure your refractive error, or what eyeglass lens is needed to correct your vision. Hyperopia is measured in terms of positive diopters. Myopia is measured in terms of negative diopters.

Diplopia: See double vision.

Disease neutral: Something that neither prevents diseases nor affects the treatment of diseases. LASIK is considered disease neutral.

Double vision: A type of distortion in which two images of a single object are seen. Common with cataracts and other eye disorders.

Dry eye: A condition characterized by corneal dryness due to inadequate tear production.

Emmetropes: People who have no refractive error; that is, no nearsightedness, farsightedness, or astigmatism. Perfect refractive ability is referred to as emmetropia.

Endophthalmitis: A serious infection, usually bacterial, of the interior of the eye.

Endothelium: The innermost layer of the cornea, a single cell thick, that helps regulate the cornea’s hydration.

Enhancement procedure: A secondary treatment with the excimer laser to fine-tune one’s visual acuity after the initial LASIK procedure. Enhancements take place after vision has stabilized, usually three to six months after LASIK. Enhancements usually do not require making a new corneal flap.

Epi-LASIK: A variant of PRK in which the epithelium (the clear skin that covers the eye) is peeled off by an automated machine called an epikeratome. The results are the same as PRK.

Epithelial ingrowth: A potential complication of LASIK produced when corneal surface cells, or epithelium, grow underneath the corneal flap during the first month after surgery. The condition is often easily diagnosed and treated.

Epithelium: The thin, protective outermost surface of the cornea. It is made up of the same kind of cells that cover most of the body. The epithelium grows rapidly and continually regenerates.

Excimer laser: The type of laser used in refractive surgery to remove corneal tissue. It emits highly precise pulses of ultraviolet light to break up tissue one molecular layer at a time, vaporizing it without generating heat that could damage surrounding tissue.

Eyelid: Thin, retractable tissue covering the front of the eye. The eyelid serves to protect the eye from dust and other foreign objects and from exceedingly bright light. It also distributes moisture (tears) over the cornea.

Eyelid speculum: A device placed between the upper and lower eyelids to keep the patient from blinking during surgery. It is painless, because the eye is anesthetized.

Farsightedness: See hyperopia.

Field of vision: See visual field.

Floaters: Particles in the vitreous humor that drift across the visual field.

Food and Drug Administration (FDA): The federal agency that regulates the manufacturers and distributors of drugs and devices. There is a popular misconception that the FDA regulates the practice of medicine. It does not; regulation of the practice of medicine is left up to the states. A related misconception is that the FDA approves medical and surgical procedures. It does not—the majority of medical and surgical procedures done in the United States are not FDA approved but rather are off-label, or unapproved.

Fovea, fovea centralis: Central concave area of the macula that is packed with photoreceptors called cones, which produce the sharpest vision.

Fundus: Interior surface of the back of the eyeball, visible with an ophthalmoscope. The eye's fundus includes the retina (with macula and fovea) and the juncture of the optic nerve with the eye.

Ghost images: Distortion of vision similar to "seeing double." With double vision, however, you'll see two relatively clear images, whereas ghost images are fainter "copies" that appear on one side of or around the object you're looking at.

Ghosting: The appearance of double images or shadows around images. Ghosting is sometimes experienced by people with astigmatism and can also result from irregular healing of the corneal surface after LASIK. See also ghost images.

Glaucoma: Group of diseases usually associated with increased intraocular pressure; if untreated, can lead to blindness.

Halo: Perceived rings around light sources viewed at night; often accompanied by starburst. A common symptom of cataracts.

Haptics: The side struts, or extensions, on an intraocular lens that help to hold it in place after implantation.

Haze: Scarring of the corneal stroma, or corneal bed. Significant haze occurs rarely after PRK, and does not occur after LASIK.

Herpes simplex: A recurrent viral infection of the eye characterized by a painful sore on the eyelid or surface of the eye. It causes inflammation of the cornea and can lead to blindness. This is not a sexually transmitted infection. Patients with herpes simplex of the eye may not be candidates for LASIK.

Higher-order aberration: Irregularity of vision that cannot be corrected by glasses or contact lenses.

Hypermature cataract: A cataract that is so far advanced it may be completely opaque and allow little or no vision in the affected eye; can cause pain and inflammation.

Hyperopia: Also known as farsightedness, hyperopia occurs when the eyeball is too short from front to back or when the eye’s focusing mechanism is too weak, causing light rays to be focused behind, rather than on, the retina. People with hyperopia see objects at a distance more clearly than close up but usually have difficulty with both distance and near vision.

Immature cataract: A cataract that is not well advanced and may not yet interfere significantly with vision.

Inflammation: A localized response to an injury that results in redness, heat, pain, and swelling and that can result in tissue damage if left untreated.

Informed consent: A legal form a patient is asked to sign that thoroughly discusses the risks, benefits, alternative options, and possible complications of LASIK.

IntraLase: A microkeratome that helps the surgeon create the flap by creating thousands of tiny laser pulses in the cornea.

Intraocular lens: A synthetic lens implanted during refractive lens exchange to replace the natural lens.

Intraocular pressure (IOP): The pressure exerted by the fluid within the eye that gives it its firmness and round shape.

IOL: See intraocular lens.

Iris: The colored ring of tissue in the eye that is behind the cornea and in front of the lens. The muscles of the iris can adjust the size of the eye’s opening, or pupil, to allow for larger or smaller amounts of light to enter the eye.

Keratectomy: Surgical removal of any part of the cornea. In the context of LASIK, keratectomy is the flap-making part of the procedure.

Keratomileusis: Any process of carving, or reshaping, the cornea.

Keratotomy: A surgical incision of the cornea.

Lamellar: An adjective meaning “layered.” Lamellar corneal surgery corrects focusing errors by removing or reshaping some of the corneal layers.

LASEK: A variant of PRK in which the epithelium (the clear skin that covers the eye) is removed by loosening it with an alcohol solution. The results are the same as those of PRK.

Laser: Acronym for light amplification by stimulated emission of radiation, a high-energy light source used medically to cut, burn, or dissolve tissues.

LASIK: An acronym for laser in-situ keratomileusis. In LASIK, a miniature automated instrument called a microkeratome creates an extremely thin, hinged flap on the surface of the cornea. After the flap is gently lifted back, the surgeon reshapes the corneal stroma, using an excimer laser. The corneal flap is then replaced, and it quickly adheres. LASIK is a safe and pain-free form of refractive eye surgery that has proven to be highly successful and popular.

Lazy eye: See amblyopia.

Legal blindness: Visual acuity with glasses of 20/200 or worse.

Lens: The globe-shaped natural lens of the eye, located behind the iris, that helps fine-tune the angle of light to bring it to a point of focus on the retina. As the lens becomes less flexible with age, its ability to adapt its focus for reading gradually decreases. See also crystalline lens.

Limbal-relaxing incisions: An astigmatism-management technique consisting of small incisions in the limbus—the thin connection between the cornea and the white of the eye (the sclera)—that cause the cornea to become more rounded when it heals.

Low vision: Poor visual acuity.

Macula: Small central area of the retina filled with light-sensitive photoreceptors called rods and cones.

Macular degeneration: A progressive eye disease caused by deterioration of the central portion of the retina, called the macula.

Mature cataract: A cataract that has advanced to the point where the lens appears milky.

Microkeratome: The instrument a surgeon uses to create the corneal flap in the uppermost layer of the cornea during the LASIK procedure.

Monofocal intraocular lens: An IOL that is similar to a disposable camera lens, in that it has a single fixed focal point, usually designed for mid-distance vision. Eyeglasses are needed for good vision at other distances.

Monovision: A process by which a surgeon corrects one eye for seeing at a distance and the other eye for seeing objects close up.

Multifocal intraocular lens: An IOL that is similar to a sophisticated camera lens, in that it automatically adjusts its focus to provide good near, mid-range, and distance vision without glasses.

Myopia: Nearsightedness, occurring when the eye is “too long” and images come into focus before they reach the retina. A nearsighted person, or myope, may have good near vision but have difficulty seeing objects at a distance.

Nearsightedness: See myopia.

Nomogram: The surgeon’s formula that is entered into the laser’s computer calculation to further refine the manufacturer’s recommended settings.

Nuclear cataract: Clouding of the center of the lens (nucleus), almost always due to aging.

Ophthalmologist: A medical doctor who specializes in the diagnosis and medical or surgical treatment of eye disorders and disease.

Ophthalmology: The field of medicine dealing with diseases and conditions of the eye.

Ophthalmoscope: An illuminated instrument used to examine structures in the back of the eye.

Optic nerve: A bundle of nerve fibers, about the diameter of a pencil, that connect to the nerve fiber layer of the retina and terminate in the brain. The optic nerve carries the visual messages from the photoreceptors of the retina to the brain, where images are created and processed.

Optical coherence biometry: Measurement of eye length using light rather than ultrasound as in an A-scan.

Optician: One who is trained to fit and dispense eyeglasses and, in some states, contact lenses, according to a prescription from an optometrist or ophthalmologist.

Optometrist: An eye-care professional specializing in the examination, diagnosis, treatment, management, and prevention of diseases and disorders of the eye. Optometrists do not perform surgery, but otherwise perform most functions that ophthalmologists do. Optometrists are often general eye-care providers and can provide preoperative and postoperative care for LASIK patients and other refractive surgery patients.

Orbit: The bony socket that surrounds the eyeball.

Orthokeratology: A technique for treating myopia by using a series of rigid contact lenses to reshape the cornea. The lenses apply pressure to the sides of the cornea, flattening them. This technique is effective for low levels of nearsightedness, but retainer contact lenses must be worn every day to prevent the effect from wearing off.

Overcorrection: A complication of LASIK, overcorrection results when the amount of correction resulting from the LASIK procedure is more than intended.

Pachymetry: Measurement of corneal thickness.

Perimeter: A device that emits flashes of light to test field of vision and reveal blind spots.

Peripheral vision: Side vision; in the visual field, perception of objects outside the direct line of vision. See also central vision.

Phacoemulsification: Surgical procedure to remove a cataract using ultrasound to break up the lens, which is then removed by suction.

Phoropter: An eye-examination device consisting of a complete range of corrective lenses that can be adjusted to hundreds of combinations, which the patient is asked to evaluate. By continually changing the lenses, the doctor can arrive at a combination of lens strengths that becomes the basis of a prescription for corrective lenses.

Photoablation: The process of removing, or vaporizing, tissue by means of laser energy.

Photoreceptor cells: Light-sensitive cells—rods and cones—on the retina that allow the eye to see in dim light, distinguish colors, and perceive contrast.

Photorefractive keratectomy (PRK): A type of laser vision correction that reshapes the cornea by ablating, or vaporizing, the corneal tissue one microscopic layer at a time, using an excimer laser. Unlike with LASIK, in which a hinged corneal flap is first made and lifted back to expose the corneal bed, with PRK the sculpting process removes the outer (epithelial) layer of the cornea as the laser energy works its way down to the corneal bed.

Piggyback intraocular lens: An IOL that is implanted on top of an existing IOL.

Posterior capsular opacification: Aftercataract; an opacity that can develop on the posterior capsule at any time after lens replacement.

Posterior capsule: The rear part of the lens capsule, which is left in place during refractive lens exchange to help support the implanted lens.

Posterior chamber: The fluid-filled area between the iris and the lens.

Posterior subcapsular cataract: A cataract that begins at the back of the lens, just under the lens capsule.

Potential acuity: A presurgical assessment of a patient’s likely visual acuity if cataracts were removed.

Presbyopia: Often confused with farsightedness, presbyopia (literally, “old eyes”) is the age-dependent need for reading glasses or bifocals, caused by the decreasing ability of the eye’s lens and surrounding muscles to fine-tune focus.

Prescription: A series of numbers that instruct someone how to provide a patient with the proper eyeglass or contact lens (see also refractive error).

Punctum plugs: Used in the treatment of dry eye, these tiny silicone plugs are inserted into the tear-drainage openings of the eyelid to delay the drainage of natural tears so the eyes will stay moist.

Pupil: Black circular opening in the center of the iris. Through muscular action of the iris, the pupil constricts or dilates to regulate the amount of light that enters the eye.

Radial keratotomy (RK): A form of refractive surgery in which the surgeon alters the shape of the cornea by making thin incisions around it in a spokelike pattern. The incisions cause the central portion of the cornea to flatten, treating myopia and astigmatism. RK is no longer performed.

Refract: To bend, as when light passes through a curved shape such as a cornea or lens.

Refraction: Bending of light as it passes from one material to another. Also, a test to determine the eye’s refractive error.

Refractive error: The eyeglass prescription needed to correct your vision. Refractive error has three parts: sphere (how nearsighted or farsighted you are), cylinder (how much astigmatism you have), and axis (the angle of your astigmatism).

Refractive lens exchange: Like cataract surgery, a procedure to remove the crystalline lens and replace it with a synthetic lens. Refractive lens exchange, however, is performed before cataracts have developed significantly, generally because the patient cannot or does not wish to wear eyeglasses or contact lenses.

Refractive surgery: Any type of surgery that changes the focusing power of the eye in order to correct a refractive error. LASIK is a type of refractive surgery that corrects the eye’s focusing ability by reshaping the curvature of the cornea.

Regression: A potential sequelae of LASIK in which the vision tends to drift back, or regress, toward its original refractive error.

Retina: The light-sensitive layer of cells on the inner back surface of the eye that processes light and functions much like film in a camera. The retina converts light into electrical impulses, which are transmitted along the optic nerve to the brain, which in turn interprets the impulses as images.

Retinal detachment: Separation of the retina from the underlying pigment epithelium, requiring immediate surgery to prevent blindness.

Retinal pigment epithelium: The part of the retina consisting of dark tissue cells that absorb excess light and carry nutrients to, and waste products from, the retina.

Ripe cataract: See mature cataract.

Rod: One of more than 120 million retinal photoreceptor cells (in each eye) that are especially receptive to brightness and allow us to see in dim light.

Sclera: The tough “white” of the eye that makes up five-sixths of the outer layer of the eyeball. Along with the cornea, it protects the eyeball.

Second sight: A temporary, cataract-induced improvement in vision among nearsighted people.

Secondary cataract: See aftercataract.

Slit lamp: A microscope that projects a flattened beam of light into the eye for close examination of internal structures.

Snellen eye chart: Standard assessment instrument for visual acuity; chart consisting of rows of letters (largest at the top, smallest at the bottom) developed by Dutch ophthalmologist Hermann Snellen in 1862; usually read at a distance of twenty feet.

Socket: The protective bony cavity that holds the eyeball.

Sphere: One of three measurements taken during an eye examination to arrive at one’s eyeglass prescription. The sphere measures where the eye focuses light—on the retina (normal vision), in front of the retina (myopia), or behind the retina (hyperopia).

Starburst: A visual aberration in which the patient sees rays radiating from lights viewed at night. Starbursts are seen by everyone, even those who haven’t had refractive surgery. Sometimes refractive surgery increases the amount of starburst the patient perceives.

Steroid: A drug used to relieve swelling and inflammation.

Striae: Wrinkles or folds in the corneal flap that are a potential complication of LASIK. Small striae, called microstriae, usually do not affect vision. Larger striae, or macrostriae, can be smoothed out easily.

Stroma: The strong, fibrous layer that makes up 90 percent of the cornea’s thickness and provides the cornea with its structure and shape. Also called the stromal bed, this is the part of the cornea sculpted with the laser in LASIK surgery.

Subcapsular cataract: See posterior subcapsular cataract

Tear: Thin film of fluid that lubricates the front of the eye. Blinking spreads tear film evenly across the surface.

Tonometer: An instrument, often used in glaucoma testing, that measures pressure of fluids inside the eye.

Tonometry: The measure of intraocular pressure, or the pressure inside the eye.

Topical corticosteroid: A medicated eyedrop that prevents inflammation of the eye tissue after LASIK surgery.

Toric intraocular lens: An IOL specially designed to correct astigmatism.

Traumatic cataract: A cataract that is caused by prior direct eye injury.

Ultrasound biometry:: See A-scan

Ultrasound: High-energy sound waves, often projected onto internal structures, creating echoes of different magnitudes that can be visualized on a television screen.

Ultraviolet radiation (UV): Electromagnetic radiation, shorter in wavelength than visible radiation but longer than X-rays; invisible rays of the sun responsible for damage to skin and eyes.

Undercorrection: A complication of LASIK; results when the amount of correction resulting from the LASIK procedure is less than intended. Most undercorrections can be treated with an enhancement procedure.

Uvea, uveal tract: Eye layer between retina and sclera that contains the iris, ciliary body, and choroid.

Uveitis: Inflammation of the uvea.

Visual acuity: The sharpness or clarity of vision that enables one to distinguish fine details and shapes.

Visual field: Extent of the area visible to an eye looking straight ahead; includes central and peripheral vision.

Vitrectomy: Surgical removal of the vitreous, which is replaced with clear fluid.

Vitreous, vitreous humor: Clear gel-like substance that fills the rear two-thirds of the eyeball between the lens and the retina.

Wavefront analysis: A measurement, performed with laser light rays, of irregularities in the focusing power of the eye. This data can be fed into the laser during LASIK and PRK procedures to correct vision to better than 20/20.

YAG laser: Yttrium aluminum garnet laser, which produces a shortpulse, high-energy light beam to cut or perforate tissue. It is used to treat posterior capsule opacification.

Zonule: One of the fibers that connect the ciliary muscle to the crystalline lens. Contraction and relaxation of the ciliary muscle change the tension of the fibers, which in turn changes the focusing power of the eye. The fibers also help to hold the lens in place.

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