Ablation zone: The area of tissue that is removed during laser surgery.

Accommodation: Ability of the eye to change its focus from distant objects to near objects.

Acuity: Clearness or sharpness of vision.

All-Laser LASIK: Surgery where a laser keratome device is used to cut a corneal flap for LASIK surgery; also referred to as "bladeless LASIK."

Astigmatism: Distortion of the image on the retina caused by irregularities in the cornea or lens.

Cornea: The clear, front part of the eye. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power.

Diopter: The measurement of refractive error. A negative diopter value signifies an eye with myopia, and a positive diopter value signifies an eye with hyperopia.

Dry eye syndrome: A common condition that occurs when the eyes do not produce enough tears to keep them moist and comfortable. Common symptoms of dry eye include pain, stinging, burning, scratchiness, and intermittent blurring of vision.

Endothelium: The inner layer of cells on the inside surface of the cornea.

Epithelium: The outermost layer of cells of the cornea; this is the eye's first defense against infection.

Excimer laser: An ultraviolet laser used in refractive surgery to remove corneal tissue.

FDA (Food and Drug Administration): The United States governmental agency responsible for the evaluation and approval of medical devices.

Flap and zap: A slang term for LASIK.

Ghost image: A fainter second image of the object you are viewing.

Glare: The scatter from bright light that decreases vision.

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

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

Higher order aberrations: Refractive errors, other than nearsightedness, farsightedness, and astigmatism, which cannot be corrected with glasses or contacts.

Hyperopia: The inability to see near objects as clearly as distant objects, and the need for accommodation to see distant objects clearly. This is commonly referred to as farsightedness.

Inflammation: The 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: A document disclosing the risks, benefits, and alternatives to a procedure.

In situ: A Latin term meaning "in place" or not removed.

Iris: The colored ring of tissue suspended behind the cornea and immediately in front of the lens.

Keratectomy: The surgical removal of corneal tissue.

Keratitis: Inflammation of the cornea.

Kerato: A prefix indicating relationship to the cornea.

Keratoconus: A disorder characterized by an irregular corneal surface (cone-shaped) resulting in blurred and distorted images.

Keratomileusis: The carving of the cornea to reshape it.

Keratotomy: A surgical incision (cut) of the cornea.

Laser (light amplification by stimulated emission of radiation): An instrument that produces a powerful beam of light that can vaporize tissue.

Laser keratome: A laser device used to create a corneal flap.

LASIK (Laser-Assisted In Situ Keratomileusis): Surgery where a flap is created in the cornea with a microkeratome, using a laser to reshape the underlying cornea.

Lens: The part of the eye that provides some focusing power; it changes shape to allow the eye to focus at different distances.

Microkeratome: A 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.

Monovision: The purposeful adjustment of one eye for near vision and the other eye for distance vision.

Myopia: The inability to see distant objects as clearly as near objects; this is often referred to as nearsightedness. 

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

Optician: An expert in the art and science of making and fitting glasses and contact lenses.

Optometrist: A primary eye care provider who diagnoses, manages, and treats disorders of the visual system and eye diseases.

Overcorrection: A complication of refractive surgery where the achieved amount of correction is more than desired.

PRK (Photorefractive Keratectomy): A procedure that involves the removal of the surface layer of the cornea (epithelium) by gentle scraping and use of a computer-controlled excimer laser to reshape the stroma.

Presbyopia: The inability to maintain a clear image (focus) as objects are moved closer; presbyopia is due to reduced elasticity of the lens with increasing age.

Pupil: A hole in the center of the iris that changes size in response to changes in lighting. It gets larger in dim lighting conditions and gets smaller in brighter lighting conditions.

RK (radial keratotomy): A surgical procedure designed to correct myopia (nearsightedness) by flattening the cornea using radial cuts.

Refraction: A test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another.

Refractive errors: Imperfections in the focusing power of the eye, for example, hyperopia, myopia, and astigmatism.

Refractive power: The ability of an object, such as the eye, to bend light as light passes through it.

Retina: A layer of fine sensory tissue that lines the inside wall of the eye. The retina acts like the film in a camera to capture images, transforms the images into electrical signals, and sends the signals to the brain.

Sclera: The tough, white, outer layer (coat) of the eyeball that, along with the cornea, protects the eyeball.

Snellen visual acuity chart: One of many charts used to measure vision.

Stroma: The middle, thickest layer of tissue in the cornea.

Undercorrection: A complication of refractive surgery where the achieved amount of correction is less than desired.

Visual acuity: The clearness of vision; the ability to distinguish details and shapes.

Vitreous humor: The transparent, colorless mass of gel that lies behind the lens and in front of the retina and fills the center of the eyeball.

Wavefront: A measure of the total refractive errors of the eye, including nearsightedness, farsightedness, astigmatism, and other refractive errors that cannot be corrected with glasses or contacts.