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A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | R | S | T | U | V

A

Ablate
In surgery, to remove.

Ablation
The vaporization of tissue with the excimer laser.

Ablation Zone (Treatment Zone)
The area of tissue that is removed during laser surgery.

ALK
See Automated lamellar keratoplasty.

Aniseikonia
A difference in the size of the image between the two eyes, so that the images cannot be seen as one.

Anterior Chamber
The fluid-filled area between the iris and lens.

Ant-inflammatory Medication
A drug that reduces inflammation or the body's reaction to injury or disease.

Aqueous
The fluid in the anterior chamber.

Astigmatism
A refractive error caused by a difference in the amount of the corneal curvature, one axis being steeper than the other at 90° ( like a football). Astigmatism is measured in terms of diopters, cylinder meridian or axis. Uncorrected astigmatism may produce ghosting or double images.

Autoimmune Disease
A medical condition in which the body attacks itself that may result in inflammation or swelling of parts of the body; such as muscles, joints, and blood vessel.

Automated Lamellar Keratoplasty (ALK)
An older refractive procedure in which the surgeon first creates a flap in the uppermost layer of the cornea using a device called a microkeratome. Then the surgeon makes an optical cut after removing additional tissue with a second pass of the microkeratome before putting the two together again.

Axis
In ophthalmology, a line that is the symmetrical center of a curved optical surface. Measurement of astigmatism.

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B

BCVA
See best corrected visual acuity.

Best corrected visual acuity (BCVA)
The best possible vision a person can achieve with corrective lenses measured in terms of the Snellen lines on an eye chart.

Bowman's Membrane
The non-regenerative layer of tissue between the epithelium and the stroma (5-10 microns thick – 05 to .01 millimeters).

Broad Beam Laser
A second-generation laser that produces a powerful beam of light that is focused at close range to remove corneal tissue. A broad beam laser uses a relatively large beam diameter to create a correction zone of approximately 5mm, and a transition zone of 2.5mm using a series of mirrors or masks.

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C

Cataract
A clouding of the crystalline lens inside the eye that can cause a loss of vision. This clouding tends to develop with older age and may affect different parts of the crystalline lens.

Central Islands
A complication of broad beam Lasers related to the ablation they create. These sometimes decrease visual acuity.

Collagen Vascular Disease
A medical condition that may result in inflammation or swelling of parts of the body; such as muscles, joints, and blood vessels.

Conductive Keratoplasty
A procedure that utilizes a controlled release of radiofrequency energy to increase the temperature of corneal tissue. The treatment is applied with a probe that is introduced 8 to 32 times into the cornea in a circular pattern, which results in an increase curvature of the cornea. This procedure was designed to treat farsightedness (hyperopia) without cutting or removing corneal tissue.

Cornea
The outer window of the eye that provides 70% of the eye's refractive power. The cornea is approximately 500 microns thick (.5 millimeter) and consists of 5 layers – epithelium, Bowman's membrane, stroma, Descemet's membrane and endothelium.

Correction Zone
The portion of the ablation providing the visual correction.

Cylinder meridian
In ophthalmology, a line that is the symmetrical center of a curved optical surface. Measure of astigmatism.

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D

Decentration
A complication caused by movement of the eye during laser ablation. The scanning laser is much more forgiving than second-generation machines, so this type of complication is rare, surgeon experience is most important in eliminating this complication.

Descemet's Membrane
The layer of the cornea between the stroma and endothelium. Five microns thick (.005 millimeters), this membrane provides an adhesion layer for the endothelial layer.

Diffused Lamellar Keratitis (DLK)
See Sands of the Sahara.

Diopters
A measurement of refractive error. Hyperopia is measured in terms of positive diopters. Myopia is measured in terms of negative diopters. The most common refractive errors ranged between +6 to -6 diopters with Myopia accounting for close to 85% of refractive errors.

Dry eye
A syndrome characterized by corneal dryness due to chemical imbalances, or deficient tear production

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E

Ectasia
A progressive corneal thinning and bulging caused by the removal of too much corneal tissue during laser ablation. Multiple surgeries greatly increase the chances of this disastrous surgical outcome as more tissue is removed. Corneas average 500 microns in thickness, leaving less than 300 microns can trigger this complication.

Emmetropes
People who have no refractive error (see 20/20 or better).

Emmetropia
The ophthalmic term for a normal refractive state – no nearsightedness, farsightedness or astigmatism.

Endothelium
The innermost layer of the cornea. The endothelium is one cell layer thick (5-10 microns or .005-.01 millimeters) and provides hydration to supply enough oxygen to maintain the cornea's transparency. The endothelium serves three main purposes it regulates the stroma's water content, provides a barrier to several constituents of the aqueous humor, and actively transports glucose.

Enhancement
A secondary refractive procedure performed after the initial one in an attempt to achieve improved visual acuity.

Epithelial in-growth
A complication of LASIK wherein epithelial cells grow underneath the corneal flap. Also known as "the sands of the Sahara". Commonly relieved by medication, but sometimes removed through corneal scraping.

Epithelium
The outermost layer of cells of the cornea. Six cells thick (20 microns), the epithelium is the eye's first defense against infection. Some of the fastest healing tissue in the body. It can regenerate in two to three days if completely removed, as in PRK.

Excimer Laser
A "cool " ultraviolet laser used in refractive surgery to remove microscopic layers of corneal tissue.

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F

Farsightedness
A term for hyperopia

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G

Glare
A complication of refractive surgery in which the patient sees additional luster around lights. Glare is usually associated with pupils that dilate beyond the treatment zone. Some people experience minor glare caused by the healing process immediately following surgery, and it decreases as the eye heals.

Ghosting
A distortion of image due to irregular healing of the corneal surface.

Globe
The eyeball.

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H

Halos
A complication of refractive surgery in which the patient sees rings around lights at night. Halos are seen when the pupil dilates beyond the correction zone, or when the eye is healing. While healing most people are not bothered by dim halos caused by this process, and they decrease as the eye heals.

Haze
A relatively rare complication of LASIK caused by the deposition of ground substance in the cornea. Outcomes for the patient include– decreased night vision, halos, or loss of best corrected visual acuity. These are caused by the eye's reaction to the laser. Haze often decreases with time and is most common with PRK.

Hyperopes
People who are farsighted.

Hyperopia
The ophthalmic term for farsightedness. In the hyperopic eye, images are focused behind the retina. The hyperopic eye is often described as having a cornea that is too flat or a globe that is too short.

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I

Intraocular Pressure
The pressure the fluid contained within the eye exerts on the globe.

Irregular Astigmatism
A refractive error caused by an irregular shape of the cornea in the optical zone post-surgically. .

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K

Kera
Pertaining to the cornea.

Keratectomy
The portion of the LASIK procedure in which the surgeon creates a corneal flap with an instrument called a microkeratome to expose the layer of the cornea called the stroma.

Keratoconous
A rare inherited condition of the cornea in which it is steepened to the point of being cone-shaped.

Keratoplasty
The replacement (transplantation) of the cornea. Keratoplasty can be lamellar (replacement of superficial layers) or penetrating (replacement of the full thickness of the cornea).

Keratotomy
A surgical incision (cut) of the cornea.

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L

Laser
An acronym for light amplification by stimulated emission of radiation. An instrument that produces a powerful beam of light and can produce intense heat or cool vaporization when focused at close range. Lasers are often used in surgery to remove tissue.

LASIK
The acronym for laser in-situ keratomileusis. The name refers the use of a laser to reshape the cornea without invading the adjacent cell layers.

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M

Meibomian secretions
Oily secretions from the eyelid glands that supply the outer portion of tear film, prevent rapid tear evaporation, and tear overflow.

Micron
One thousandth of a millimeter. The symbol for a micron is µ.

Monovision
The purposeful adjustment of one eye for near vision and the other for distance vision accomplished with either corrective lenses or surgery.

Myopes
People who are nearsighted.

Myopia
The medical term for nearsightedness. The cornea is too steep, or the eye is too long resulting in an image that is focused in front of the retina. (See illustration)

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N

Nomogram
The numbers necessary to refine the laser's computer calculation based upon the history of past clinical study results. These numbers are then further refined by each surgeon to improve his own results.

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O

Off Label Use
The permissible use of an approved drug or instrument in a way that has not been specifically sanctioned by the FDA but is legal since it is at the physician's discretion.

Optic Nerve
The millions of optical nerve fibers connecting to the eye and terminating in the brain where images are created and processed.

Over-correction
The result achieved when the change to refractive error exceeds the attempted correction.

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P

Pachymetry
The process of measuring corneal thickness.

Photorefractive Keratotomy
A procedure involving the removal of the surfaces layer of the cornea (epithelium & Bowman's) by scraping and the subsequent use of a computer-controlled excimer laser to reshape the stroma. Acronym is PRK.

Plano
Characterized by no refractive error.

Presbyopia
The natural deterioration of near vision caused by loss of flexibility in the eye's lens as one ages.

PRK
The acronym for photorefractive keratotomy. A procedure involving the removal of the surface layers of the cornea (epithelium & Bowman's) by scraping, and subsequent use of a computer-controlled excimer laser to reshape the stroma.

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R

Radiofrequency Energy
A form of electrical energy (radio waves) utilized by the ViewPoint CK system and commonly used by other medical devices.

Refraction
The bending of light waves as they pass from one medium to another.

Refractive surgery
Any surgical procedure that attempts to decrease the patient's refractive error. Typically the surgeon alters the shape of the cornea in order to change the focal length of an image projected onto the retina.

Regular Astigmatism
A refractive error caused by the cornea having a steeper and more shallow curve at 90° to one another similar to the shape of a football.

Retina
Light processing membrane; converts light into electrical impulses that are transmitted to the brain via the optic nerve.

RK
Acronym for radial keratotomy. A surgical procedure designed to correct myopia (nearsightedness) by flattening the cornea with incisions. The procedure is called a radial keratotomy because the incisions resemble the spokes in a wheel.

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S

Sands of the Sahara
A term used to describe a sandy, or gritty, looking treatment zone post-operatively. Usually caused by epithelial in-growth.

Slit Lamp
Table-top binocular microscope for examining the eye.

Snellen Chart
An eye chart composed of lines of letters and numbers of diminishing size, used to test a patient's vision.

Snellen line
A line of same-sized letters on an eye chart that is used to test a patient's vision.

Scanning Laser
The Nidek EC-5000: A third-generation laser that uses a beam of light that is moving around the eye in a computer controlled pattern to accomplish the removal of corneal tissue. Scanning lasers use less energy, have a larger zone of correction, and provide faster healing

Stroma
Thickest part of the cornea (450-600 microns– approximately .5 millimeters). Between Bowman's membrane and Decemet's membrane.

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T

Tear Film
A very thin film of eye and related fluids riding on top of the front surface of the eye that lubricates and oxygenates the cornea.

Topical Proparacain Hydrochloride
Anesthetic eye drops.

Treatment Zone
The area of tissue that is removed during laser surgery.

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U

UCVA
See uncorrected visual acuity.

Uncorrected Visual Acuity (UCVA)
A person's vision without corrective lenses measured in terms of Snellen lines on an eye chart. Acronym is UCVA.

Undercorrection
The visual result when desired change in refractive error is not fully achieved.

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V

Vitreous
The gel-like fluid in the main cavity of the eye behind lens and pupil.

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