Glossary of Terms

AK	Astigmatic Keratotomy.
Astigmatism	Astigmatism is an uneven curvature of the cornea resulting in blurry vision. An astigmatic patient may be more curved on one side of the cornea than the other. Astigmatism can result in an inability to focus clearly at any distance, because light rays entering the eye are bent unequally by the cornea, preventing the formation of a sharp point of focus on the retina. Astigmatism often occurs in conjunction with myopia or hyperopia.
Cataract	A cataract is a clouding of the normally clear lens of the eye. It can be compared to a window that is frosted or fogged with steam. Cataracts are surgically removed and a manufactured lens implant is installed to restore clear vision.
Central optical zone	The central optical zone is usually a 3-4mm diameter area around the center of the cornea through which visual images pass. The central optical zone is critical for clear vision.
Cornea	The clear, dome-shaped "window" at the front of the eye that covers the iris and pupil. The cornea plays an important role in vision because it is the main focusing part of the eye, accounting for approximately 75 per cent of the eye's light-focusing power. It is made of hundreds of layers of tissue.
Cornea Transplant	Replacing of a damaged cornea with a clear donor cornea that is sewn into place.
Corneal Periphery	The area of the cornea outside the central optical zone, also where Intacs are placed.
Diopter	Unit used to measure the amount of correction in your glasses or contact lens (nearshightedness, farsightedness and astigmatism).
Dry Eyes	Some people do not produce enough tears to keep the eye comfortable. This condition is known as dry eye. Eye drops, or artificial tears, can be used to lubricate the eye and help maintain moisture.
Enhancement	Repeating a refractive surgical treatment to achieve more improved visual acuity. This is may be done after three months following LASIK, if a surgeon feels it is medically safe.
Excimer laser	A medical device to emit laser energy created by a mixture of argon-fluoride gases. Used in photorefractive kerotectomy (PRK) and LASIK (laser-assisted intrastromal keratoplasty) to reshape corneal curvature by ablating, or burning off, tissue from the center of the cornea.
Glare	Sensitivity to bright lights coming at the eye from various angles.
Glaucoma	Glaucoma is one of the leading causes of blindness, if left untreated. Common open-angle glaucoma is the most common type. Lack of proper drainage within the eye causes pressure to build that damages the optic nerve and leads to vision loss. Proper monitoring and eye medications can control pressures so as to prevent blindness.
Halo	Rings of light or fuzz around lights often seen a night.
Hyperopia	Hyperopia, or farsightedness, is a focusing problem, which occurs when the cornea is not curved enough, or the eye is shorter than normal. The reduced length means the light rays focus behind the retina, producing a blurred image.
Intacs® (Corneal Rings)	Two clear, ultra-thin, precision-engineered crescents, each with an arc length of 150 ^o, that can be placed in the periphery of the cornea of the eye to correct myopia. Placed outside of the central optical zone, Intacs are designed to reshape corneal curvature without cutting or removing tissue from the optical zone, which is the critical area for clear vision. This subtle reshaping is intended to make nearsighted corneas flatter, thereby correcting vision. In the United States, the Food and Drug Administration have approved Intacs for commercial use.
Iris	The pigmented tissue behind the cornea that gives color to the eye (blue, brown, hazel, etc.) and controls the amount of light entering the eye by varying the size of the pupillary opening.
Keratoconus	Keratoconus is an abnormality of the cornea structure that may lead to astigmatism. Many patients who wear rigid contact lenses experience this condition. Such patients are not candidates for LASIK.
LASIK	Laser in-Situ Keratomileusis (see Excimer Laser).
Lens	A structure inside the eye that helps to focus light on the retina. It is curved on both sides and acts similar to a camera lens.
Microkeratome	The instrument used by the surgeon to cut a thin flap on the front of the cornea prior to performing LASIK. Following the procedure, this natural flap is then put back in place to protect the surface of the eye.
Myopia	Myopia, or nearsightedness, is the most common vision problem, affecting approximately one in four people. People with myopia can clearly see objects up close but not those at a distance. Myopia occurs when the cornea is curved too steeply, or the eye is longer than it should be. In myopic eyes, light rays from distant objects are focused in front of the lens, so that the image projected on the retina is blurred.
Optic Nerve	Acts as a cable to carry images received by the eye to the processing center in the brain, making sense of what is seen.
Over and/or Under Corrections	Patients are advised during the informed consent process that under or over correction from laser surgery may occur as a risk of the procedure. There are no guarantees. Depending upon the degree of under or over correction, the physician will advise the patient as to the possibility of conducting an enhancement following the initial surgery.
Presbyopia	As the eye undergoes the natural aging, around 40 to 45 years of age, the eye looses its ability to fine focus and one experiences a vision change that often requires reading glasses. Refractive surgery does not eliminate or reduce this natural process, but may reduce dependency on glasses.
PRK	Photo-Refractive Keratectomy.
Pupil	The black, circular opening in the center of the iris (the colored portion of the eye). The pupil controls the amount of light that enters the eye.
Refraction	A measure of the eye's focusing power.
Refractive error	A defect in the ability to focus light rays precisely on the retina. Common refractive errors are myopia, hyperopia and astigmatism, affecting approximately half the world's population.
Regression	Regression is the development of nearsightedness or farsightedness that may occur several months or years after initial surgery.
Retina	Like the film in a camera, the retina records the images received by the eye and sends them to the brain through the optic nerve.
RK	Radial Keratotomy.
Stroma	The middle tissue layer that compromises approximately 90 percent of the cornea. The stroma is composed of densely packed layers similar to the pages of a book. Intacs are designed to be placed within these layers.
Vision correction surgery	Also known as refractive surgery. In addition to Intacs (corneal rings), techniques include radial keratotomy (RK), photorefractive keratectomy (PRK), laser assisted intrastromal keratoplasty (LASIK), and automated lamellar keratoplasty (ALK). According to the medical literature, all but Intacs involve premanent removal of tissue from the central optical zone, the critical area for clear vision.