Laser Eye Surgery, PRK, LASIK

What is PRK and LASIK

In this section you will find out what exactly PRK is, what's involved with the procedure and the results of PRK treatment in terms of safety and history.
Disclaimer - Care and professional advice is required.

Introduction LadarVision Custom Cornea
RK - The Beginning of Eye ReShaping
PRK - The Modern Choice
for Vision Restoration
PRK - Predictability and Safety
NEW!! -
For detailed information with pictures (photos) of an actual LASIK procedure, please visit our sister web site


Throughout history, mankind has experimented with ways to improve vision with external aids and instruments. Although glasses and contact lenses have provided many people with a reasonable quality of life, they still have limitations. Glasses have improved through the use of modern lightweight lenses and grinding techniques - such as bifocals and reading glasses. And designers have improved the look of glasses to the point that now certain types of frames are a required fashion statement. But for many lifestyles, glasses are very inconvenient. And for some people they do not give the quality of vision desired.
The advent of contact lenses in the 50's addressed some of the inconveniences of glasses. The apparent invisibility of contacts was great for people who were self-conscious about wearing glasses. In some cases, people could engage in activities that were previously prohibitive with glasses - such as athletics, physically active careers, or just an intimate evening with a loved one. But wearing contact lenses also has a price. In addition to the purchase price (which have dropped dramatically in the past few years), the wearer now must spend what amounts to considerable time and money both in the maintenance and in the application of their contacts. There still remains a limitation as to the types of activities one can participate in, and lastly, long term lens wearers may develop an intolerance to wearing their lenses as well as long term damage.
As a result of the limitations of both of the above visual aids, ophthalmologists (eye doctors) were keen to come up with better ways to provide improved vision. The last frontier was to make modifications to the eye itself - to correct the actual aberration that was causing poor vision in the first place. And it is this practice that the next section is devoted to explaining.


Before the appearance of computers and laser beams, the main tools available to an ophthalmologist were a scalpel, a steady hand, a medical background and perhaps some engineering knowledge. The premise was that if they could modify the shape of the cornea, then possibly they could effect permanent improvement to their patient's vision. (The cornea is the clear dome on the front of the eye, it is in reality a lens which provides about 80% of the focus power of the eye.) The first procedure to show the possibility of achieving a positive result was called radial keratotomy or RK.

What is RK?

Radial Keratotomy (RK) is described as "a surgical operation to improve myopia by changing the curve of the cornea over the pupil. The surgeon makes several deep incisions in the cornea in a radial or spoke-like pattern." The incisions are intended to flatten out the central cornea to correct the patient's vision."

Myopia, or nearsightedness is caused by your cornea being more domed than necessary - the light enters your eye and focuses at a point in front of your retina. (The retina is the part of your eye that receives visual information and sends it to your brain.)

To put that into layperson's language, the qualified eye surgeon would make a series of cuts (usually 4 to 8) in the cornea with a scalpel, in a pattern that resembles a spoked wheel (pink lines in photo right). These cuts are fairly deep, sometimes to 90% of the thickness of the cornea. As you can see from the diagram below, these "V" cuts cause the central cornea to relax or flatten and the peripheral cornea to steepen, reducing the dome of the central cornea with a resulting improvement in uncorrected vision.

The cuts are created with a special diamond bladed scalpel. Lasers have been used to make these cuts but with little improvement in results.
Even with lasers and computers, the older "standard" type of RK has been found to have major shortcomings and limitations. Firstly, RK can only be used to correct low amounts of myopia. It cannot address the problems of hyperopia (farsightedness). The main drawback is the 90% thickness weakening of the cornea which frequently leads to progressive flattening of the cornea and increasing farsightedness.
There is a school of thought in the USA that newer types of RK with much shorter incisions such as Mini and/or Midi RK do not suffer from the serious structural weakening of earlier forms of RK operations. The more modern operations are said not to have the same risk of future progressive farsightedness.

Complications at the time of surgery are rare, but can be serious. The following is a list of some of the potential long term complications:

  • fluctuating vision, especially the first few months after surgery;
  • a weakened cornea that is more vulnerable to rupture if hit directly;
  • the need for additional refractive surgery;
  • difficulty fitting contact lenses should they be required;
  • glare or starbursts around lights (haze).

It is the opinion of this Webmaster that "standard" RK has too many risks associated with it to consider it a safe alternative to visual aids. The facts that the cornea is seriously weakened and frequently continues to change shape with time, are major detriments to recommending "standard" RK especially now that the technology of PRK is available. It is also believed that despite the better safety and success of "Mini" RK that PRK is now the refractive operation of choice and that the use of RK will rapidly decline. You must obtain thorough professional advice from a qualified eye surgeon or surgeons before proceeding with RK treatment.

What is PRK?

The most recent development in vision correction is a procedure called Photorefractive Keratectomy or PRK. Although the approach is similar to RK, in that the cornea is modified to correct vision, the process is vastly different with remarkable improvements in patient risk and correction capabilities.

Rather than making cuts in the cornea, the PRK process uses an excimer laser to sculpt an area 5 to 9 millimeters in diameter on the surface of the eye. As you can see from the diagram, this process removes only 5-10% of the thickness of the cornea for mild to moderate myopia and up to 30% for extreme myopia - about the thickness of 1 to 3 human hairs. The major benefit of this procedure is that the integrity and the strength of the corneal dome is retained. The excimer laser is set at a wavelength of 193nm, which can remove a microscopic corneal cell layer without damaging any adjoining cells. This allows the practitioner to make extremely accurate and specific modifications to the cornea with little trauma to the eye.

This ability to sculpt, rather than cut, opens up the arena for treating additional vision conditions. At this stage, there are excimer laser machines that with a combination of masks and computer controls, can reliably treat myopia, hyperopia and now astigmatism.

PRK- Predictability and Safety

Although PRK sculpts only a tiny amount of tissue from the cornea, it is a surgical procedure and thus the outcome cannot be guaranteed. Any surgical procedure should be undertaken only after careful consideration of the likelihood of success and consequences of any possible risks or side effects. Thorough professional advice from a qualified eye surgeon or surgeons is required before any eye treatment is undertaken. Predictability can be defined in several ways- we favor a percentage approach to achievement of visual goals, with 20/20 uncorrected vision being ideal and 20/40 uncorrected vision being okay or acceptable. Uncorrected vision of 20/40 still allows driving without glasses. Most PRK facilities and machines report that 65-70% of patients with correction up to -6.00 diopters can expect 20/20 uncorrected vision post operatively. The percentage with 20/40 uncorrected acuity is 90-95%. Corrections less than -6.00 diopters will have better odds and corrections greater than -6.00 will have lower odds. The safety of the procedure is judged on the basis of the chance of a possible complication. Serious complications are extremely rare. Infection is the most worrisome complication and fortunately it can usually be eliminated with antibiotic medications. Other possible problems include delayed surface healing, corneal haze and or scarring, over or undercorrection, and the development of astigmatism. Some individuals can have a poor or excessive healing response. Again most complications remain treatable with medications or further surgery.

It is also important to separate the normally expected side effects of surgery and healing from real complications. Immediately after surgery some people have discomfort, although the use of bandage contact lenses and medications usually control this nicely. Light sensitivity is almost universal and halos and other unusual light effects can occur. Vision can be reduced while healing and from the normally planned overcorrection. Medical professionals and their associates consider this treatment as experimental as longterm side effects are not yet known. You must discuss and fully understand all of these possible side effects and problems prior to surgery. Hopefully, the information here will assist you in that process.

Murray McFadden MD., Inc. provides Online information by way of Internet for communication and review purposes only. Murray McFadden MD., Inc. does not have editorial control over and has not participated in the development of the materials provided here, other than those materials copyrighted in favour of Murray McFadden MD., Inc. himself, nor has Murray McFadden MD., Inc. exerted any control or participated in the development of other Internet sites which may contain informational materials of a similar nature to those found here. Murray McFadden MD., Inc. disclaims any and all liability for any injury or other damages which may result from the communication or review of information contained here.

Materials produced here are not intended to provide medical information. Rather, the materials are presented for informational purposes only. None of the materials presented may be relied upon by any person for any medical, diagnostic or treatment reasons whatsoever. None of the materials presented here may be relied upon by any person for purpose other than informational purposes without the express written consent of Dr. Murray McFadden or the person indicated as the owner of the relevant materials. Dr. Murray McFadden disclaims any liability for any injury or other damages resulting from the review or use of the information obtained here. Dr. Murray McFadden asks that any person reviewing the materials presented here obtain specific medical advice and answers to specific medical questions, by a qualified eye doctor.
For detailed information with actual photos of the LASIK procedure, please visit our sister web site

PRK & LASIK Today Home Page

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
Fax: (604) 535-6258
SnailMail: 20434 64th Avenue, Unit #201,
Langley, BC Canada V2Y 1N4

This page last updated on September 29, 2004.
Web Page Programmer Turnaround Type and Graphics