Aberration - Blurred or distorted image quality that results from inherent physical properties (shape, curvature, density) of an optical device (lens or prism).

Ablation - The removal of material, similar to vaporization. With respect to laser eye correction, 'ablation' represents a cold laser, gently yet totally removing eye material, usually with no scarring.

Astigmatism - (uh-STIG-muh-tism) The visual defect attributable to the presence of an elliptical (egg-shaped) rather than spherical shape in the refracting surfaces of the eye. This results in the diffusion of light rays with one axis being more in focus than the other.

Axis – The visual axis that represents our line of sight.

Capsule – A thin membrane that contains the natural lens of the eye.

Cornea - (KOR-nee-ah) This is the clear structure at the front central part of the eye, imparting the greatest focusing power of all the ocular media.

Enhancement - A second eye treatment, usually three to six months after the primary treatment, which corrects any minor adjustments.

Excimer Laser - An excimer laser is a cold laser that does not burn or cut. What it does do is vaporize tissue by breaking bonds between molecules. It is an extremely precise way of removing corneal material without causing damage.

Hyperopia - Long/farsightedness. In this visual defect, the eye focuses rays of light at a focal point behind the retina. A hyperoptic eye is not able to clearly see objects that are nearby.

Incision - Cutting into.

Iris - The colored portion of the eye, just behind the cornea, that controls how much light enters the eye by expanding and contracting the 'black' opening, or pupil.

Keratome - A knife or blade used for corneal incision.

Keratomileusis (KER-uh-toh-mih-LOO-sis) - A method of removing tissue from the center of the optical zone in the cornea.

Keratopathy (ker-uh-TOP-uh-thee) - Any abnormality with the cornea.

Keratoplasty (KER-uh-toh-plas-tee) - Replacing (transplanting) a scarred or diseased cornea with clear corneal tissue from a donor.

Keratotomy - Incision of the cornea.

LASEK - Laser Epithelial Keratomileusis - A form of surface ablation in which the top layer of corneal cells is treated with alcohol and removed. The flap of cellular tissue is replaced but it eventually dies off due to the toxic effects of the alcohol. Visual recovery is slower than with PRK or ASA.

LASIK - Laser in situ Keratomileusis - A procedure for the correction of myopia, hyperopia and astigmatism in which a microkeratome is used to make a corneal flap, to provide access to the surface of the cornea for the subsequent laser ablation. The flap is replaced for faster recovery.

Microkeratome - An instrument that cuts a predicted amount of tissue from across the cornea. Acts in similar fashion to a carpenter's plane.

Myopia - Short/near sightedness. Visual defect where the eye focuses rays of light at a focal point in front of the retina. A myopic eye is not able to clearly see objects that are in the distance.

Ocular - Refers to items that are part of or associated with 'the eye', e.g. ocular movement = eye movement.

Presbyopia - (prez-bee-OH-pee-uh) - Physiological aging of the eye, where the eye loses the ability to clearly focus when changing from distant objects to close objects.

PRK - Photo Refractive Keratectomy - A procedure in which excimer laser ablation of the surface of the cornea is used to correct myopia, hypermetropia and astigmatism (without the raising of a corneal flap).

Pupil - A black circular opening in the front of the iris. The pupil can expand and contract to control how much light enters the eye.

Recurrent Erosion - A superficial condition of the cornea where microscopic blisters form then break, producing minute ulcers or erosions. These spontaneously heal within a few hours but produce a burning sensation while they persist.

Refract Refraction - The bending of light as it passes from one medium into another medium of different density (e.g. as light passes from the air into the cornea). When testing a patient's vision, the ability to focus (bend light to form an image on the retina) is measured. Hence the error is called a 'refractive error'.

Refractive Error - Strictly speaking, means parallel light rays are not brought to a sharp focus on the retina, so a blurred retinal image is produced. The image formed at the back of the eye is deformed because the eye parts are not focusing the light correctly.

Refractive Surgery - Any surgery that changes the way the eye refracts (bends) light is referred to as refractive surgery.

Stromal Bed - The material under the surface of the cornea.

Vitreous humor - Jelly-like substance that fills the eyeball between the lens and retina.

Wave Print Orbscan - A sophisticated measurement device measuring the optical distortions as light exits the eye, to aide in fully customized vision correction.