Ablation: The removal of a precise amount of eye tissue during LASIK to correct the refractive error and
improve vision.
Astigmatism: A condition, usually caused by an irregularly shaped cornea, that causes blurred
vision. Instead of being spherical, like a baseball, the cornea is oblong, like a football.
Cornea: The transparent front part of the eye that covers the iris and pupil; it allows light to travel into the
eye and provides most of the eye’s refractive power.
Corneal topographer: A device that measures the curvature of the cornea and detects
irregularities on its surface.
Custom LASIK: Also called wavefront or wavefront-guided LASIK, custom LASIK is similar to traditional
LASIK surgery, but offers more individualized and precise vision correction. In addition to treating vision
problems that are corrected by glasses or contact lenses, custom LASIK also treats irregularities known
as higher-order aberrations, which cause problems such as glare, halos, shadows and poor night vision.
High-order aberrations (HOA): Irregularity of the eye that can cause vision problems, which cannot be
corrected by the use of contact lenses or glasses. If present, you might experience symptoms such as
glare, halos, double vision and difficulty seeing at night.
Hyperopia: Farsightedness, a condition in which people can see distant objects clearly but have
blurry near vision. People who are farsighted have a shorter eye than normal, causing light rays to
focus behind the retina, instead of on it.
LASIK (Laser-assisted in situ keratomileusis): A surgical procedure to reduce nearsightedness,
farsightedness and astigmatism by reshaping the tissue in the cornea. A microkeratome is first used to
create a thin flap in the cornea that is lifted; an excimer laser is used to reshape the underlying corneal
tissue and the flap is replaced over the treated area.
Microkeratome: A precision surgical instrument used in LASIK to create a flap in the cornea.
Myopia: Nearsightedness, a condition in which people can see near objects but have blurry
distance vision. People who are nearsighted have a longer eye than normal, causing light rays to
focus in front of the retina, instead of on it.
Presbyopia: An age-related condition in which the natural lens loses elasticity, which impairs the
eye’s ability to focus on near objects. Presbyopia resembles hyperopia, but is a different condition.
Refractive surgery: A procedure, such as LASIK, that corrects vision and reduces or eliminates
the need to wear glasses or contact lenses.
Retina: Nerve tissue that forms a membrane lining inside the eye. Light passes through the
lens, which creates an image and transmits it to the retina. The retina, in turn, converts this optical
information into electrical pulses that travel across the optic nerve to the brain.