Glossary

GLOSSARY

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

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

Accommodation: The ability of the eye's lens to fine-tune focus by flexing-becoming more or less convex-as needed. Accommodation can compensate for minor focusing problems in younger people whose lens and surrounding muscles are still limber and pliable.

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

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 ibuprofin.

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

Astigmatism: A refractive error caused by an asymmetrically shaped cornea. Rather than being round in shape like a basketball, an astigmatic cornea is shaped like a football, causing light to come to several points of focus instead of meeting at a single point of focus. People with astigmatism experience blurred images or double vision.

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.

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.

Blended vision: See monovision.

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!

Cataract: Clouding of the natural lens within the eye, causing blurry vision.

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.

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.

Constrict: To become smaller.

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

Crystalline lens: See lens.

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

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.

Dilate: To become larger, as when the pupil enlarges in very dim light conditions.

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.

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

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

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.

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.

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 with PRK.

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 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.

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.

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.

Glaucoma: A disorder of the eye characterized by an increase of pressure within the eyeball.

Halo: A complication of LASIK in which the patient sees a glow around lights at night. Halos usually decrease over time.

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.

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.

Induced astigmatism: A rare complication of LASIK in which astigmatism develops after the initial surgery. Most people can tolerate a small degree of astigmatism. In more serious cases, induced astigmatism can be treated with an enhancement, if necessary.

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 laser-based microkeratome that helps the surgeon create the flap by creating thousands of tiny explosions in the cornea. The surgeon then dissects the flap free with a blunt separator. Some surgeons prefer the Intralase microkeratome, while others prefer the newer automated microkeratomes that do not require manual dissection of the flap.

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

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.

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

Laser thermal keratoplasty (LTK): A technique that uses heat energy to change the shape of the cornea and that is designed to correct only low amounts of farsightedness. A special laser is used to deliver laser energy to the peripheral cornea to slightly tighten the fibers and thereby steepen its curvature. The LTK procedure may also be useful for treating occasional overcorrection from LASIK procedures. It is similar to conductive keratoplasty (see chapter 11) but has largely been abandoned, because it was found that the effect wore off too quickly.

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.

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.

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.

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

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

Myopia: Also known as nearsightedness, myopia is due to a cornea that has too much curvature or to an eyeball that is too long, causing light to be focused in front of, rather than on, the retina. People with myopia 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.

Nonfreeze keratomileusis: The process of reshaping the corneal disc directly on the eye without having to remove the disc and freeze it for the purpose of reshaping, as was done in early lamellar surgeries, precursors to LASIK.

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

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

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.

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 many of the 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.

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.

Peripheral vision: The ability to see objects and movement outside of, or on the periphery of, one's direct line of vision.

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

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.

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: The small black dot, or opening, in the center of the iris. The pupil changes its diameter in response to changes in lighting.

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 not performed anymore.

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

Refraction: The art of measuring the refractive error of the eye. Also, a synonym for 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 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 complication 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.

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.

Scleral expansion bands (SEBs): Used in surgical reversal of presbyopia, these thin silicon bands are implanted in the sclera to expand the equator of the eye, ostensibly to restore accommodation and relieve presbyopia. The theory behind SEB is that expansion of the eye will allow increased room for the lens to move normally, enabling the eye to see nearby objects again. A number of studies now suggest that this procedure is ineffective.

Snellen eye chart: The standard eye chart used by eye doctors to determine visual acuity.

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 may be seen by people who wear eyeglasses and contact lenses, and are sometimes experienced by patients who have undergone LASIK.

Striae: Wrinkles or folds in the corneal flap that are a potential complication of LASIK. Small striae, call 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.

Surgical reversal of presbyopia (SRP): See scleral expansion bands.

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.

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.

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

Vitreous humor: The gel-like substance, composed of about 99 percent water, that fills the main cavity of the eye between the lens and the retinal wall.

Wavefront analysis: A measurement, performed with laser light rays, of irregularities in the eyeball.

About The Authors »