Laser Eye Surgery, PRK, LASIK

Glossary Continued - O to Z


OCUFEN® Flurbiprofen sodium 0.03%

Non steroidal anti-inflammatory eyedrop used to reduce pain after PRK. Manufactured by Allergan.

ophthalmic (Gr. ophthalmos =eye )

Anything to do with the eye.

ophthalmologist (Gr. ophthalmos =eye)

A medical doctor who specializes in the eye. To become an Ophthalmologist one must first obtain a Medical Degree (M.D. in North America) and then complete further specialty training. A medical degree typically takes 7 or 8 years university training and a specialist certification an extra 3 years in the USA or 4 years in Canada. Specialist MD's are usually divided into "medical" and "surgical" disciplines and Ophthalmology is technically a "surgical" discipline. Some Ophthalmologists chose not to perform surgery and can be called "medical ophthalmologists".


An expert in the art and science of making and fitting glasses. (I'll have to find out the training time.)

optometrist (Gr. optos =seen + metron =measure)

(or Doctor of Optometry) is an indepedent primary health care provider who specializes in the examination, diagnosis, treatment, management and prevention of diseases and disorders of the visual system, the eye and associated structures as well as the diagnosis of related systemic conditions. Optometrists today most often complete a Bachelor of Science degree (with very specific requirements) followed by the four year Optometry degree program (6-8 years). Patient contact begins in the second professional year with the final year being a full 12 month internship. Most optometrists include provision of Contact Lens and Spectacle devices as part of their daily practice.


A complication of PRK where the expected amount of correction is more than desired. See glossary entry "regression". Overcorrection occurs in the occasional person where healing occurs less vigorously than predicted by the laser computer program, and the planned treatment "overcorrection" persists. Overcorrection can also occur in the uncommon event that the laser is improperly calibrated.

pachymetry (Gr. pachy =thick, thickness + L. meter =instrument used in measurement)

Measuring of the thickness of the cornea with ultrasound machine. The purpose of measuring is to determine the thickness of the cornea prior to PRK or LASIK treatment, so as not to exceed the maximum treatment depth. In RK the radial cuts are usually set at 90% of the depth (thickness). PRK and LASIK treatment depths are dependent upon the ablation diameter. For more information please refer to Table of Ablation Depth vs. Diopters & Diameter of Optical Zone.


An optical instrument containing many lenses which is used to determine the power of glasses or refractive error.

photo (Gr. phos, photos =light)

photoablation (Gr. phos, photos =light + L. ablatio =remove)

The "cold" process of tissue removal which occurs with laser radiation in the 200nm wavelength range. This far-UV wavelength possess light photons so powerful that the molecular bonds of the target tissue both break down and have sufficient extra kinetic energy to fly off the surface; hence ablation. Microscopic pictures show incredibly precise cuts with no evidence of tissue burning in adjacent tissue.

photocoagulation (Gr. photos =light + L. coagulatio =clot)

The process of tissue destruction accomplished by visible light radiation. Tissue is broken down by the light and "clots" as if it were cooked.

photovaporization (Gr. photos =light + L. vapors =steam or gas)

The process of tissue destruction as occurs with infra red light radiation such as with a yag laser. The target tissue is ionized causing plasma formation followed by a shock wave.

pinguecula (L. pinguis =fat)

A yellowish spot seen on the white of the eye at the junction of the clear cornea and white sclera of the eye. These lesions are usually caused by UV radiation. The white surface of the eye cannot "tan" and therefore cannot protect itself from sunburn.

PRED FORTE® prednisolone acetate 1%

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

PRED MILD® prednisolone acetate 0.12%

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

presbyopia (Gr. presbyo =old + opia =eye)

"Old eye" is a condition in which the ability to accommodate for near vision falls off because of loss of elasticity of the crystalline lens of the eye and weakness of the ciliary muscle. The individual is no longer able to read clearly and requires reading glasses.

PRK - Photo Refractive Keratectomy

Sculpting of a myopic or hyperopic lens for refractive reasons on the front surface of the eye with the use of a "cold" laser light.

PTK - Photo Therapeutic Keratectomy

"Cold" laser removal of surface tissue of the cornea such as scar tissue for medical or optical treatment reasons.

ptygeria (Gr. ptergion =wing)

A growth of scar tissue on the cornea. These lesions like pinguecula are caused by an ultraviolet burn to the surface layer or epithelium.


Pertaining to the radius or line from a circle center to the circle itself.

radial keratotomy

A surgical operation where 90% thickness cuts are made in the cornea. These cuts are made in a radial fashion and spare the visual center of the cornea. The intention is to flatten the central cornea.

regression (L. regressio = a return)

A return to the original refractive state. In PRK the surface layer or epithelium is removed prior to or as part of the procedure and then the deeper corneal stroma is reshaped with the cold laser treatment. During healing both the surface epithelium and the deeper corneal stroma can reshape and reform at different rates. Computer generated PRK treatments assume a normal "Bell" curve amount of healing for both layers and thus normally "over correct" the refractive error in order to finally heal with no refractive error and no need for glasses. A small percentage of patients will heal faster and more vigorously than expected and will thus regress or "heal" their planned over correction back past no refractive error to their original type of error. This regression phenomenon occurs with both myopic and hyperopic corrections. It occurs more commonly with smaller ablation diameters and with abrupt transition zones at the edge of the laser treatment areas. Some surgeons have suggested that the epithelium overgrows as if nature abhors a vacuum and overreacts to fill in the space. Steroid medications can usually be used to regulate and control regression.


The light sensitive nerve layer which converts light images into electrical signals for transmission to the brain. The retina can be compared to the film of a camera. See Peter's diagram.


See enhancement.


Abbreviation for Radial Keratotomy.


A large class of pharmaceutical agents that chemically resemble cholesterol. Two better known types are anabolic steroids as used illegally in athletics, and glucocorticoid steroids which are used to reduce inflammation. This latter drug type is used in PRK to regulate regression and reduce post PRK inflammatory haze.


A medical equipment and pharmacological company that markets the argon fluoride excimer laser in North America.


Manufacturer of argon floride excimer laser machines - Excimed UV200 and Omnimed.

topography - (see corneal topography)

The accurate and detailed description or drawing of places or items and their surface details. Used to determine the corneal profile in order to program the PRK computer for refractive correction as well as for post-operative corneal analysis.

UCVA - uncorrected visual acuity

This is the best vision measurement taken without the use of glasses or contact lenses.


A complication of PRK where the expected amount of correction is less than desired. See glossary entry "regression". Undercorrection occurs in the occasional person where healing occurs more vigorously than predicted by the laser computer program. Undercorrection can also occur in the uncommon event that the laser is improperly calibrated.


Manufacturer of argon floride excimer laser machines VisX 2015, VisX 2020, and VisX STAR.

vitreous humor

The jelly like material which fills the space between the lens and retina within the eye. See Peter's diagram.

VOLTAREN OPHTHAx Diclofenac Sodium 0.1%

Non steroidal anti-inflammatory eyedrop used to reduce pain after PRK. Manufactured by CIBA Vision.

wave length

The distance between the top of one wave and the top of the next wave. The argon fluoride excimer wavelength is 193 nm. This wavelength is in the far ultraviolet end of the electromagnetic spectrum.

yag laser

A laser type using an infra red wavelength of 1064 nanometers. The laser material is neodymium Yttrium-Aluminum-Garnet. Yag lasers are used after cataract surgery to photovaporize the residual membrane behind the artificial lens. The commom misconception that "lasers" are used to remove cataracts occurs because c. 75% of post-cataract patients eventually require yag laser capsulotomy.
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)

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