Glossary

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Ablate
In surgery, to remove.
Acuity
Clearness or sharpness of vision.
Aphakic
Refers to a condition in which there is no lens in the eye. Aphakia is usually a result of trauma or surgery.
Aqueous Humor
The fluid produced by the ciliary body and found predominately in the anterior chamber of the eye. Regulation of the production and removal of this fluid regulates the pressure inside the eye.
Astigmatic Keratotomy (AK)
A form of refractive surgery that corrects astigmatism by making one or two incisions at the steepest part of the cornea. These incisions cause the cornea to relax and take a more rounded shape.
Astigmatism
A condition in which the uneven curvature of the cornea blurs and distorts both distant and near objects. In astigmatism the cornea is less round and more elliptical.
Basement Membrane
The part of the corneal epithelium that serves as the foundation on which the epithelial cells anchor and organize themselves.
Bowman’s Layer
A transparent sheet of tissue located directly below the basement membrane of the corneal epithelium.
Collagen
Collagen is a tough, glue-like protein that represents 30 percent of body protein and shapes the structure of tendons, bones, and connective tissues. Collagen gives the cornea its strength, elasticity, and shape.
Collagen Vascular Diseases
Generally considered autoimmune diseases in which a patient’s immune system attacks their own collagen-containing systems. Examples of collagen vascular diseases include: rheumatoid arthritis, systemic lupus erythematosus, scleroderma, dermatomyositis, and polyarteritis nodosa.
Conductive Keratoplasty (CK)
A type of refractive surgery that uses mild heat from radio waves to shrink the glue-like connective tissue called collagen in the periphery of the cornea.
Contraindications
Medications or preexisting conditions that make a planned course of therapy inadvisable due to a high likelihood of an adverse reaction.
Cornea
The clear outer part of the eye’s focusing system located at the front of the eye. The cornea covers the colored part of the eye or iris.
Corneal Edema
Swelling of the cornea.
Corneal Endothelial Cells
The individual cells which together form the endothelial layer. The number of these cells decreases with age. Damaged endothelial cells cannot be replaced and must be compensated for by existing cells. Excessive loss of endothelial cells with result in corneal edema.
Corneal Endothelium
The extremely thin, innermost layer of the cornea. Endothelium is essential in keeping the cornea clear. Normally, fluid leaks slowly from inside the eye into the middle corneal layer, or stroma. The endothelium’s primary task is to pump this excess fluid out of the corneal stroma.
Corneal Epithelium
The cornea’s outermost layer, making up about 10 percent of the cornea’s thickness. The job of the epithelium is to block the passage of foreign material, such as dust, water, and bacteria, into the eye and other layers of the cornea. The epithelium also provides a smooth surface that absorbs oxygen and cell nutrients from tears, and then distributes these nutrients to the rest of the cornea. The epithelium is filled with thousands of tiny nerve endings that make the cornea extremely sensitive to pain when rubbed or scratched.
Corneal Haze
Corneal clouding that causes the sensation of looking through smoke or fog.
Corneal Stroma
The central layer of the cornea which consists primarily of collagen, and does not contain any blood vessels. The stroma makes up about 90 percent of the cornea’s thickness.
Custom Ablation
Refers to the customization of laser vision correction treatments for the individual patient. Custom ablation corrects for multiple abnormalities or aberrations within the visual pathway beyond simple refraction.

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Descemet’s Membrane
One of the inner most layers of the cornea covered on one side by the corneal endothelium and by the corneal stroma on the other. Descemet’s membrane is a thin but strong sheet of tissue composed of collagen fibers that serves as a protective barrier against infection and injuries.
Excimer Laser
An ultraviolet laser that allows ophthalmologists to remove very precise amounts of tissue from the eye’s surface during refractive surgery in order to improve the patient’s vision.
Farsightedness
The common term for hyperopia.
Fovea
The center of the macula within the retina. The fovea provides the sharpest vision and is responsible for reading vision. It is approximately the size of the tip of a pen.
Glaucoma
A group of eye diseases that are usually characterized by elevated intraocular pressure levels and damage to the optic nerve that result in progressive loss of peripheral vision. Left untreated, glaucoma can result in complete loss of vision.
Ghost Image (Ghosting)
A more faint second image of the object you are viewing.
Glare
Scatter from bright light that decreases vision.
Halos
Rings around lights due to optical imperfections in or in front of the eye.
Higher Order Aberrations
Errors within the visual pathway, other than nearsightedness, farsightedness, and astigmatism, that cannot be corrected with glasses or contacts.
Hyperopia (Farsightedness)
The opposite of myopia. Distant objects are clearer, and close-up objects appear blurry. With hyperopia, images focus on a point beyond the retina. Hyperopia generally results from an eye that is short. With refractive surgery, hyperopia is treated by steepening the cornea.

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Implantable Collamer Lens (ICL)
Sometimes called phakic lenses, these are lenses made of plastic or silicone that are implanted into the eye permanently to reduce a person’s need for glasses or contact lenses.
Inflammation
The body’s reaction to trauma, infection, or a foreign substance, often associated with pain, heat, redness, swelling, and/or loss of function.
Intrastromal Corneal Rings (ICR)
Small devices implanted in the eye to correct vision, typically used for patients with mild to moderate nearsightedness. Also used for keratoconus; only approved in military for keratoconus.
In Situ
A Latin term meaning “in place” or not removed.
Iris
The colored part of the eye that regulates the amount of light entering the eye. The center opening of the iris is known as the pupil.
Keratoconus
A disease of the cornea characterized by an irregular corneal surface (cone-shaped), resulting in blurred and distorted images.
Laser-Assisted In Situ Keratomileusis (LASIK)
A form of laser refractive surgery in which a flap is made in the outer layers of the cornea. The flap is elevated and the corneal stroma is reshaped with an excimer laser permanently changing the shape of the cornea. The flap is then returned to its original position.
Laser-Assisted Sub-Epithelial Keratomileusis (LASEK)
LASEK is a form of laser refractive surgery in which the epithelium is chemically separated from the cornea prior to laser treatment and replaced following the laser procedure.
Laser Thermal Keratoplasty (LTK)
A type of refractive surgery in which a laser is used to treat farsightedness and astigmatism. During LTK, a laser beam uses heat to shrink and reshape the cornea. LTK is used to treat farsightedness or astigmatism.
Lens
A structure within the eye located behind the iris, which focuses light on the retina. Clouding of the lens is known as a cataract.
Lid Speculum
An instrument used to hold a patient’s eyelids open during a procedure.
Macula
A small area of the retina which is responsible for the most detailed vision and has the highest concentration of cells which detect color.
Microkeratome
A surgical device, which is used in LASIK to create the corneal flap. The device 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.
Myopia (Nearsightedness)
The opposite of hyperopia. Myopia is a refractive error in which near objects appear clearer and distant objects appear blurry. In myopia, the eye is usually longer than normal or the cornea is steeper than normal. As a result, the image is focused in front of the retina. Myopia is treated with laser refractive surgery by flattening the cornea.

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Nearsightedness
The common term for myopia.
Ocular Disease
Is defined as problems which occur in the eye, eyelids, eyelashes, or lacrimal (tear) system.
Optic Nerve
A bundle of more than one million nerve fibers that carries visual messages from the retina to the brain.
Phakic
The natural condition of the eye in which the lens is in place.
Photorefractive Keratectomy (PRK)
A type of laser refractive surgery for correcting many cases of refractive error. In PRK, the vision correction is performed on the surface of the cornea after the epithelium has been removed. The epithelial cells then heal over the following three to four days, in order to cover the cornea. No corneal flap is made during PRK.
Presbyopia
Refers to the loss of the ability to focus on near objects that is associated with normal aging of the lens in the eye and the muscles that control the shape of the lens. This commonly occurs after age 40, when the lens of the eye becomes more rigid and does not flex as easily.
Pseudophakic
The condition of the eye when the natural lens has been removed and an artificial lens has been implanted, such as following cataract surgery.
Pupil
The opening at the center of the iris through which light passes to the retina. The iris adjusts the size of the pupil and controls the amount of light that can enter the eye.
Radial Keratotomy (RK)
A refractive procedure that involves making of a number of cuts in the cornea to change its shape and correct refractive errors. This procedure is performed using a diamond blade scalpel.
Refractive Errors
A collection of vision disorders including myopia, hyperopia and astigmatism in which the light is not properly focused on the retina. This results in a blurry image and is treated with glasses, contact lenses or refractive surgery.
Refractive Surgery
An elective procedure intended to correct common eye disorders, known as refractive errors, such as nearsightedness, known as myopia, farsightedness, also known as hyperopia, and distorted vision, which is referred to as astigmatism. Refractive surgery is designed to alter the shape of the cornea in order to improve the patient’s vision.
Retina
The light-sensitive tissue, which lines the back of the eye. The retina converts light into electrical impulses that are sent to the brain through the optic nerve. The retina is often compared to the film in a camera.
Vitreous Gel
A clear gel that fills the posterior chamber of the eye and consists primarily of specialized collagen fibers and water.