Laser Eye Surgery, PRK, LASIK


In this section we have provided a comprehensive glossary of terms used by vision care professionals, as well as some of the products used in the profession. This is provided to assist you in the comprehension of vision correction procedures. If you have any questions or know of a term that is not addressed here, please submit a query on the Guest Book page and we will respond with the information.

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LADARVision Custom Cornea




Ketorolac Tromethamine- non steroidal anti-inflammatory eyedrop used to reduce pain after PRK. Manufactured by Allergan.

ablation (L. ablatio =removed )


acuity (L. acuitas =sharpness)

Clearness as in visual acuity. The most common measure of visual acuity is the Snellen Acuity- completely normal acuity being 20/20 or 6/6 (metric version).

amblyopia (Gr. amblys =dull + Gr. ops =eye)

Poor vision without any visible abnormality of the eye. Synonym= lazy eye.


Abbreviation for Astigmatic Keratotomy


Ophthalmic Equipment and Drug Company. Manufacturer of the LADARVision® System and Custom Cornea®


Abbreviation for Automated Lamellar Keratectomy.


Ophthalmic Equipment and Drug Company.

ametropia (Gr. ametros =disproportionate + ops =eye + -ia )

Any imperfection in refractive state of the eye- i.e. hyperopia, myopia, or astigmatism.

argon laser

Laser light produced from argon gas. The main wavelengths are 488.0 nm blue and 514.5 nm pea green light, but nine separate wavelengths in the blue-green visible light spectrum are produced.

astigmatism ( a=negative + Gr. stigma=point )

A refractive abnormality where light is not focused to a point on the retina. This is often caused by the cornea or front window of the eye being elliptical (shaped more like an egg) rather than spherical (shaped like an orange). Refractive correction includes a lens which has focusing power in one axis and no power in the opposite axis. The amount of astigmatism you have will appear in the second number of most glasses prescriptions ie - 4.00 -1.00 x 30°, or -5.00 +1.00 x 120. In both of the above cases you would have 1.00 Diopter of astigmatism.

Autonomous Technologies Corporation

Manufacturer of the T-PRK® excimer scanning laser.

BCVA Best Corrected Visual Acuity

This is a measure of best corrected acuity or in other words the best acuity while wearing glasses or contact lenses- the best your eye can see.

binocular (L. bini =two + oculus =eye)

Both eyes.


The process of measuring and setting the laser to the needed energy for accurate tissue removal. Some machines sculpt a PMMA plastic button to be measured by optical instruments, and others employ a 1 micron thick foil as a method of calibration.

cataract (L. cataracta =to break down)

A cloudiness or opacity of the normally clear lens of the eye.

central island

A complication of PRK where the laser beam fails to remove a portion of cornea- usually in the center of the area to be removed. If one views the concave area of the ablation like a lake one can imagine an island sticking up in the center- the visual symptoms would be monocular double vision or distortion- just as you would expect if there were an irregularity in the surface of your glasses.


Manufacturer of excimer laser "Technolas Keracor 116".

CIBA Vision Ophthalmics

Ophthalmic Equipment and Drug Company


Manufacturer of argon floride excimer laser machine - Keratom.

concave lens

A lens with a hollow shape like the inside surface of a ball. Concave lenses are - (minus) power lenses and are used to correct myopia or near-sightedness.


The delicate mucous membrane that lines the eyelids and covers the white surface of the eye. The conjunctiva joins the eyeball at the edge of the cornea (limbus).

convex lens

A lens with a bulging surface like the outer surface of a ball. Convex lenses are +(plus) power lenses and are used to correct hyperopia or far sightedness and for reading glasses as needed in presbyopia.

cornea (L. corneus =horny)

The transparent front window of the eye. Light passes into the eye allowing vision and also out of the eye allowing the iris and pupil of the eye to be seen. The cornea can be considered to have 5 layers:
  • 1. the corneal epithelium,
  • 2. Bowman's layer,
  • 3. corneal stroma,
  • 4. Descemet's layer, and
  • 5. the corneal endothelium.

corneal endothelium (Gr. endon =within)

The inner layer of cells on the inside surface of the cornea- like the inside pane of a double pane window.

corneal epithelium (Gr. epi =on)

The outer surface layer of the cornea, like the epidermis or outer layer of the skin.

corneal haze

An opacification or cloudiness of the normally clear cornea. Any build up of inflammatory infiltrates (white blood cells), extra moisture, scar tissue, or foreign substances (like drugs) can cause a clouding of the cornea. Most types of haze will disappear with time or drug treatment but sometimes permanent haze or scars can form.

corneal topography

A process of mapping the surface details of the cornea with a unique camera/computer combination. Used to determine corneal slope and astigmatism for PRK refractive correction. Also used post-operatively to measure the results of PRK treatment. The computer data can manipulated to show the efficacy of ablation and the quality of smoothness of the final refracted surface.

corneal topographical map

The linked map is an example of corneal topography which shows the surface profile of the cornea.


In perfect centration the center of the PRK corneal ablation exactly coincides with the center of the visual axis and/or pupil. This is like looking through the very center of your spectacle lens. If you look through the periphery of your lens you might end up seeing partly through the lens and partly through the edge of the lens- this is decentration. Decentration can cause various symptoms including edge glare or even monocular double vision. Other factors such as the normal size of the pupil, whether it is dark out (your pupil will enlarge) or the size of the PRK ablation zone will affect the severity or presence of symptoms.

diopter (Gr. dioptra =optical instrument for measuring angles)

The diopter is the unit of measurement for optical lenses. A one diopter lens will focus parallel light rays 1 meter from the lens and a two diopter lens will focus 0.5 meter from the lens. A plus ( + ) 1.0 diopter lens is convex and will converge the light rays so they focus as a visible image 1 meter past the lens. A minus ( - ) 1.0 diopter lens is concave and will diverge or spread light. The minus lens will not actually focus as a visible image on an optics table. Its image is known as a virtual image and if the divergings rays were followed to their point of origin they would focus 1 meter in front of the minus lens.

diplopia (Gr. diplous =double + Gr. ope =sight)

Double vision or seeing double usually with both eyes open as in binocular diplopia, but can be with only one eye as in monocular diplopia.

emmetropia (Gr. emmetros =in proper measure + ope =sight + -ia)

Perfect distance vision without the need of glasses.

endo (Gr. endon =within )

A prefix meaning within or inside.

endophthalmitis ( Gr. endon =within + ophthalmia =eye + itis =inflammation )

An inflammation within the eye. Inflammations may be caused by organisms such as bacteria or may be sterile as in immune disorders. Endophthamistis usually is used to indicate an infectious disease as occasionally occurs as a complication of surgery.


Extra laser treatments made to refine or improve the original visual result. See glossary entry "regression" for discussion of normal, slow, and vigorous healing. It is important to appreciate that although refractive predictability is excellent at lower planned corrections, that predicability is reduced at higher corrections. Higher corrections and wider optical zones require deeper sculpting and consequently undercorrection and overcorrection are more common. Enhancement treatment by contrast is usually a small correction and usually has a highly accurate outcome.

excimer laser

Laser energy produced by several rare gas- halide mixtures. The term excimer comes from the concept of an energized molecule with two identical components or excited dimer (contracted to one word exci-mer). In PRK the term has for practical purposes become synonomous with the argon-fluoride (ArF) gas version. The wave length of an ArF excimer laser is in the far ultraviolet range at 193 nm.

EyeSys Laboratories

Corneal Topographical Mapping Systems

flap & zap

A term meaning LASIK.

far sighted

A refractive abnormality of the eye requiring a plus (positive or convex) lens for correction. The term originated because people who are far or distance sighted can see at a distance more clearly than they can see objects which are closer. The medical term is hyperopia or hypermetropia.

FLAREX® - Fluoromethalone acetate 0.1%

Corticosteroid eyedrop used to reduce corneal haze and regulate healing response after PRK. Manufactured by Alcon.

FML® - Fluoromethalone 0.1%

Corticosteroid eyedrop used to reduce corneal haze and regulate healing response after PRK. Manufactured by Allergan.

FML FORTE® - Fluoromethalone 0.25%

Corticosteroid eyedrop used to reduce corneal haze and regulate healing response after PRK. Manufactured by Allergan.

Humphrey Instruments

Ophthalmic Equipment

hyperopia (Gr. hyper =above + ops =eye + -ia)

A refractive abnormality of the eye requiring a plus (positive or convex) lens for correction. Synonyms: far sighted, hypermetropia. Far or distance sighted people can see at a distance more clearly than they can see objects which are closer.


Ending of word used in names to indicate condition or disease state.

immune (L. immunis =safe)

Protected against a disease or danger.

immune system

The body's internal defense system which defends you from dangers such as infections, cancer, etc. Normal healing is coordinated with the immune system. Occasionally abnormal immunity can cause problems such as iritis or arthritis. These conditiions are referred to as auto-immune conditions meaning your immune system becoming confused and attacking your body.

INFLAMASE® FORTE - Prednisolone Sodium Phosphate 1.0%

Corticosteroid eyedrop used to reduce corneal haze and regulate healing response after PRK. Manufactured by Iolab.

INFLAMASE® MILD - Prednisolone Sodium Phosphate 1/8%

Corticosteroid eyedrop used to reduce corneal haze and regulate healing response after PRK. Manufactured by Iolab.

inflammation (L. inflammatio; inflammare =to set on fire)

A tissue's reaction to trauma often with pain, heat, redness, swelling, and or loss of function. Inflammation may be caused by mechanical trauma, infections by bacteria or viruses, and by immune reactions, and other causes.


An ending term meaning inflammation.


Ophthalmic Equipment and Drug Company

kerato (Gr. keras =horn , cornea)

A prefix indicating relationship to the cornea or window of the eye. Kerato also can indicate a relationship to horny tissue.

keratitis (Gr. keras =horn , cornea + itis =inflammation)

An inflammation of the cornea. Inflammation may be caused by trauma as in an abrasion, RK, or PRK; or be caused by infections by bacteria or viruses; or be caused by immune disorders.

keratoconjuntivitis (Gr. keras =horn , cornea + conjuntiva + itis =inflammation)

An inflammation (infectious or auto-immune) of the cornea and conjunctiva.

keratoconus (Gr. keras =horn , cornea + knous =cone)

An abnormality of the eye where the cornea becomes deformed in the shape of a cone. This condition is a contraindication to (or strong reason against having) refractive surgery such as PRK or RK.

keratomileusis (Gr. keras =horn, mileusis =chiselling)

A refractive surgical technigue where a partial thickness circular flap of cornea is removed, frozen, lathed to a new shape and replaced upon the cornea. The lathe can shape either a convex or concave lens.

keratectomy (Gr. keras =horn, cornea + ektome =excision)

Surgical excision (removal) of any portion of the cornea. In a penetrating keratectomy (or PK) a button-like full thickness segment of the cornea is removed and replaced with a donor cornea from another person.

keratotomy (Gr. keras =horn, cornea + temnein =to cut)

Surgical incision of the cornea as in radial keratotomy ie. a radially or clock hour aligned incision in the cornea.

laser An acronym for Light Amplification by the Stimulated Emission of Radiation.

Laser light is different from ordinary light in that it is:
  • 1. composed of one color ( wavelength ) and
  • 2. traveling in one direction and each light wave is
  • 3. traveling in step with the adjacent wave making the laser light
  • 4. more powerful by a factor of millions of times over light energy produced by non laser sources.

Energy is carried by the wave in "packets" of energy called Photons. Albert Einstein's Quantum theory helps to explain the physics of lasers. Albert Einstein received his Nobel Prize for the Quantum theory (rather than the theory of relativity).

Lasersight Technologies, Inc.

Manufacturers of the Lasersight(SM), Compak-200 Mini-Excimer(TM) and Laserscan 2000(TM) Photopolishing System. These are 193nm excimer scanning systems.

LASIK An acronym for Laser in Situ Keratomileusis.

A surgical operation where a flap of surface cornea is cut and rolled aside in order that a laser beam can remove internal tissue from the inside (stroma or body) of the cornea. Following removal of tissue the surface layer is reattached. The amount and shape of the removed tissue is determined by the preoperative refractive error i.e. myopia, hyperopia or astigmatism.

limbus (L. limbus =border)

The visible borderline between the clear window (cornea) and the white globe (sclera) of the eye. The conjungtival layer which covers the globe also joins at the limbus. (see illustration x)

masks (Fr. masque =to cover or conceal)

Masks are used in PRK surgery to modify the removal of surface tissue by the laser. PRK surgery involves the removal of or fashioning of concave (myopic) or convex (hyperopic) lenses on the corneal surface. Most refractive errors also include some element of astigmatic irregularity. Most excimer laser machines employ different kinds of masks to customize, refine and smooth the corneal surface. Many machines have an internal constricting diaphragm (like a camera f-stop mechanism) as an internal mask for use in treating Myopia. One manufacturer uses an extra material applied unto the cornea (an ablatable or destroyable mask) for treating astigmatism. Another manufacturer uses a different shaped metal mask for treatment of hyperopia or myopia. Variable rotation of the masks is used to deal with astigmatism.


A shortened name for the Aesculap-Meditec excimer laser company.

micrometer abbrev.: um = 10 to the -6 power meter.

The term micrometer has replaced the term micron which was used prior to 1967.

micron A micrometer or 10 to the -6 power meter.

The term micron was used prior to 1967.

millimicron A nanometer or 10 to the -9 power meter.

The term millimicron was used prior to 1967.

myopia (Gr. myein =to shut + ops =eye + ia)

A refractive abnormality of the eye requiring a minus (negative or concave) lens for correction. Synonyms: near sighted or short sighted. People who are near sighted can see objects up close or at near without glasses.

nanometer abbrev.: nm = 10 to the -9 power meters

The term nanometer has replaced the term millimicron which was used prior to 1967.

near sighted

A refractive abnormality of the eye requiring a minus (negative or concave) lens for correction. The term originated because people who are near sighted can see up close more clearly than they can see objects which are in the distance. The medical term is myopia.

Nidek Technologies

Manufacturer of argon floride excimer laser machine - EC-5000.


Manufacturer of solid state laser machine - Lightbladex.


Abbreviation for non steroidal anti-inflammatory drug.

Glossary Continues - O to Z
For detailed information with actual photos of the LASIK procedure, please visit our sister web site

For more information contact:
Dr. Murray McFadden
(BSc, MD, FRCS(C), Diplomate of the American
Board of Ophthalmology)

© Copyright 1996-2005 Murray McFadden MD, Inc.

Telephone: (604) 530-3332
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This page last updated on November 9, 2004.
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