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Glossary



Ablate: To remove by erosion, evaporation or vaporization.

Accommodation: The eye's ability to change its focus from distance to near objects, a process achieved when the lens changes shape.

Accommodative Intraocular Lens: A permanent lens replacement that functions similar to the natural eye. After surgical insertion the eye can focus on near, intermediate or far objects. Often glasses will not be needed following the surgery.

Amblyopia (Lazy Eye): A disorder of the coordination between the eye and the brain, usually beginning in childhood that causes the body to prefer one eye over the other, leading to unequal vision.

Aniridia: A congenital condition in which the iris is absent or partially absent. May also result from trauma to the eye. For additional information on Aniridia click here and see our Study for Patients with Traumatic or Congenital Aniridia.

Anterior Chamber: The space in front of the iris and behind the cornea.

Aqueous Humor: Clear, watery fluid that flows between and nourishes the lens and cornea.

Astigmatism: A condition that occurs when an uneven curvature of the eye causes light to be refracted (bent) unevenly, resulting in distorted vision.

Automated Lamellar Keratoplasty: A refractive surgery procedure used to treat relatively high degrees of myopia and some cases of hyperopia. This procedure uses only the microkeratome and is not as accurate as the laser procedures that are currently available.

Binocular Vision: The blending of separate images seen by each eye into a single image, allowing images to be seen with depth perception.

Blepharitis: A chronic inflammatory condition of the eyelids, common in children and adults, which causes redness, burning, itching, swollen and crusty lid margins and dry-eye symptoms.
Blepharitis Video by Avenova

Blind Spot: A small area of the retina where the optic nerve enters the eye which occurs normally in eyes, or a gap in the visual field corresponding to an area of the retina where no visual cells are present.

Bowman's Membrane: The micro-thin second layer of the cornea that lies just below the epithelium, or outer layer.

Cataract: A gradual opacity or clouding of the normally clear crystalline lens of the eye, caused by the natural aging process, metabolic changes, injury, various forms of radiation, toxic chemicals and certain drugs.

Central Retinal Artery: The blood vessel that supplies nourishment to the retina.

Choroid: The layer filled with blood vessels that nourish the retina.

Ciliary Muscles: The muscles that relax the zonules to enable the lens to change shape for focusing.

Ciliary Processes: The extensions or projections of the ciliary body that secrete aqueous humor.

Collagen: Protein fibrils within the corneal tissue that help sustain its shape.

Concave Lens: A prescription lens that is curved to correct for a cornea that is too convex in shape, resulting in nearsightedness.

Cones and Cone Cells: Specialized, light-sensitive cells (photoreceptors) in the retina that provide sharp central vision and color vision.

Conjunctivitis: An inflammation of the eye's outer membrane, which causes redness, swelling, itching and watering in one or both eyes.

Contrast Sensitivity: The ability to perceive differences between an object and its background.

Convex Lens: A prescription lens, shaped like a discus, to treat farsightedness by correcting for a cornea that is too concave, or flat.

Cornea: The outer, transparent, dome-like structure that covers the iris, pupil and anterior chamber and serves as part of the eye's focusing system.

Corneal Disease (Keratitis): A deep infection and inflammation of the cornea caused by an abrasion, inflammation or the presence of bacteria or fungi in the cornea.

Corneal Ulcer: A condition of the cornea that occurs when localized tissue has eroded, usually causing a red, painful eye.

Diabetic Retinopathy: A common complication of diabetes in which the blood vessels in the retina, often causing loss of vision.

Dilation: A process by which the pupil is temporarily enlarged with special eye drops to allow examination of the interior of the eye.

Diopter: A unit of measurement used to describe the degree of refractive error with respect to nearsightedness, farsightedness and astigmatism.

Drusen: Tiny yellow or white deposits in the retina or optic nerve head.

Dry Eye Syndrome: A condition caused by the reduction in quality and quantity of tears. For additional information on Dry Eye Syndrome, please see the Dry Eye topic under About Your Eyes.

Ectropian: A condition that occurs when the lower eyelid turns outward, which may result in dry eye symptoms and excessive tearing.

Endothelium: A thin layer of cells lining the under surface of the cornea that pump fluid from the cornea, keeping it clear.

Entropian: A condition in which the lower eyelid turns inward, causing irritation.

Flashes and Floaters: A condition that occurs when the back of the eye is filled when a jelly-like substance (vitreous gel) becomes increasingly more liquid-like in nature, causing small particles, called floaters, to become visually evident. Flashes originate from the tugging on the retina as the vitreous gel liquefies.

Fluorescein Angiography: A test to examine blood vessels in the retina, choroid and iris in which a special dye is injected into a vein in the arm and images are captured as the dye passes through blood vessels in the eye.

Focal Point/Focus: The refraction of light rays by the cornea and the inner lens to a focal point on the retina in a precise, natural manner that produces sharp, clear and colorful images.

Fovea: The central part of the macula that provides the sharpest vision.

Fundus: The interior lining of the eye, including the retina, optic disc and macula, which can be seen during an eye examination by looking through the pupil.

Glaucoma: A vision-threatening disease that can cause optic nerve damage, most often from high pressure caused by poor drainage of a fluid (aqueous humor) which supplies nutrients to the cornea and lens.

Herpes Zoster (shingles):An infection, produced by the same virus that causes chicken pox that may reactivate on the skin or in the eye, causing inflammation and scarring.

Hordeolum (stye): A red, painful, swollen, cyst-like bump of the eyelid caused by a localized inflammatory process.

Hyperopia (Farsightedness): A condition that occurs when the cornea is too flat and/or the eye is too short, which causes light to be focused behind the retina, leading to blurred vision.

IOL: Intraocular lens implant.  An artificial lens that is implanted inside the eye.

Intraocular Pressure: Pressure of the fluid inside the eye, which varies among individuals.

Iris: The colored ring of tissue, suspended behind the cornea and immediately in front of the lens, which regulates the amount of light entering the eye by adjusting the size of the pupil.

Iritis: An inflammation of the colored part of the eye, or iris, resulting in an eye that is red, painful and sensitive to light.

Keratoconus: This condition arises when the middle of the cornea thins and gradually bulges outward, becoming cone shaped, producing moderate to severe astigmatism and blurriness. Click here for more information on Intacs for the treatment of keratoconus.

Keratometer: A sophisticated instrument that measures the frontal curvature, or steepness of the cornea, comparing high and low points to determine if a refractive problem exists.

Lacrimal Gland: The small, almond-shaped structure, located above the outer cornea of the eye, which produces tears.

Laser: The acronym for Light Amplification by Stimulated Emission of Radiation, which is used in vision correction procedures and refractive surgery.

LASIK: The acronym for Laser In Situ Keratomileusis, which is a revolutionary vision-correction procedure for the treatment of nearsightedness, farsightedness and astigmatism.

Legal Blindness: Visual acuity of 20/200 or worse in the better eye with corrective lenses, or a visual field restriction of less than 15 degrees.

Lens: The transparent, double convex structure suspended between aqueous and vitreous, which helps to focus light on the retina.

Lensectomy: A procedure that replaces the natural lens of the eye with a prescription lens for cataracts and severe cases of nearsightedness and farsightedness.

Limbus: The outer perimeter of the cornea which joins the sclera.

Low Vision: Visual loss, which cannot be corrected with eye wear or contact lenses and interferes with daily living activities.

Macula: The small, sensitive area of the central retina that provides vision for fine work and reading.

Macular Degeneration: A condition caused by the breakdown of the macula, the center part of the retina, resulting in gray, hazy or blocked vision.

Microkeratome: A sophisticated surgical instrument that is used in LASIK and refractive surgery to sculpt micro-thin layers of corneal tissue.

Micron: A unit of length equal to one-thousandth of a millimeter.

Monovision: A refractive correction, achieved with lenses or LASIK, which uses one eye for distance and one eye for near vision.

Myopia (Nearsightedness): A condition that occurs when the cornea is too steep and/or the eye is too long, causing light to be focused in front of the retina, which results in blurred vision.

Nevus: A benign, pigmented lesion that can occur in the eye.

Nomogram: A procedure that uses instruments to measure the contour of the eye, the internal pressure and other refractive factors.

Ophthalmologist: A physician who has received advanced training to specialize in the medical science that deals with the structure, functions and diseases of the human eye.

Optic Cup: The white, cup-like area in the center of the optic disc.

Optic Disc/Optic Nerve Head: The circular area (disc) where the optic nerve connects with the retina.

Optic Nerve: The bundle of over a million nerve fibers that carry visual messages from the retina to the brain.

Optical Zone: The central area of the cornea that performs a majority of the refractive functions of the eye.

Optometrist: A professionally licensed doctor who prescribes eye wear, contact lenses, low vision aids and vision therapy for adults and children. They also may treat eye diseases, such as infections, allergic conditions and glaucoma, as well as providing pre- and post-operative care for surgical patients.

Peripheral Vision: Side vision; ability to see objects and movement outside of the direct line of vision.

Phoropter: An instrument used to determine the degree of myopia, hyperopia or astigmatism present in the eye.

Pinguecula: A slightly raised, yellowish thickening of the white part of the eye (conjunctiva) adjacent to the cornea, typically caused by repeated sun and wind exposure.

Phakic: Refers to an eye that possesses its natural lens.

Posterior Chamber: The space between the back of the iris and the front face of the lens that is filled with aqueous fluid.

Presbyopia: A condition, becoming symptomatic around age 40, in which the focusing muscles of the eye become fatigued and, in time, become unable to focus up close.

Pterygium: A wedge-shaped growth on the cornea that can cause irregular astigmatism, warping of the cornea, and possibly potential vision loss.

Ptosis: A condition, attributed to age, trauma, a neurological disorder and/or lid manipulation, such as contact lens wear, that causes the upper eyelid to droop.

Pupil: The adjustable opening at the center of the iris that allows varying amounts of light to enter the eye.

Radial Keratotomy (RK):A surgical procedure to correct mild to moderate cases of nearsightedness and some cases of astigmatism that involves placement of patterned surgical incisions in the peripheral area of the cornea to correct nearsighted refractive errors.

Refraction: A test to determine the best eye wear or contact lenses to correct a refractive error (myopia, hyperopia or astigmatism).

Retina: The light-sensitive layer of tissue that lines the back of the eye and sends visual messages through the optic nerve to the brain.

Retinal Detachment: A potentially vision-threatening condition that occurs when the retina separates from the supporting structures in the rear of the eye.

Retinal Pigment Epithelium (RPE): The pigment cell layer, located just outside the retina and attached to the choroids, that nourishes the retina cells.

Rods and Rod Cells: Specialized light-sensitive cells (photoreceptors) in the retina that provide side vision and the ability to see objects in dim light (night vision).

Schlemm's Canal: The passageway in which the aqueous fluid leaves the eye.

Sclera: The tough, white outer layer of the eye that, with the cornea, protects the eye.

>Strabismus (Crossed Eyes): Misaligned eyes, not only crossed, but an eye that may gaze outward, upward or downward in the relaxed position.

Stroma: The third and thickest layer of tissue of the cornea.

Subconjunctival hemorrhage: A condition that occurs when a blood vessel of the white part of the eye (conjunctiva) breaks and bleeds, resulting in a reddened eye.

Suture: A surgical strand used to close an incision.

Systemic Disease: A disease that affects the body in more than one specific area.

Thermokeratoplasty: A refractive procedure that uses a laser to heat and shrink tissues in the peripheral area of the cornea in order to change the shape and correct cases of farsightedness and/or astigmatism.

Tonometry: The means to determine the fluid (intraocular) pressure inside the eye.

Topography: An advanced test that maps the curvature of the cornea to evaluate it for irregularities.

Trabecular Meshwork: The spongy, mesh-like tissue near the front of the eye which allows the aqueous fluid (humor) to flow to Schlemm's canal and out of the eye through ocular veins.

Ultrasonic Pachometer: The instrument used to measure the thickness of the cornea.

Uvea, Uveal Tract: The middle coat of the eye, consisting of the choroids in the rear and the ciliary body and iris in front of the eye.

Visual Acuity: The ability to distinguish details and shapes of objects.

Visual Field: The entire area that can be seen with the eye, including peripheral vision.

Vitreous: The transparent, colorless mass of gel that lies behind the lens and in front of the retina.

Wavefront: The use of light images to evaluate the way that waves of light pass through the visual system to detect problems with the way in which the eye handles light.

Wavescan Systems: New technology that records a "fingerprint" or precise, detailed analysis about the visual characteristics of the entire optical system. The information is integral to planning a more personalized approach to LASIK laser vision correction.

Yag Capsulotomy: A quick, painless laser procedure to treat the posterior capsule, which improves cloudy vision by allowing light to more effectively reach the retina.

Zonules: The fibers that hold the lens suspended in position and enable it to change shape during accommodation.

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