Laser Vision Correction - PRK and LASIK Procedure         

Using an excimer laser we are able to reshape the surface of your cornea so that light rays entering the eye will now be in focus on the retina.  In PRK (photorefractive keratectomy) the treatment occurs on the surface of the cornea.  With LASIK (Laser In-Situ Keratomileusis) the treatment occurs under a flap cut in the cornea.  Both procedures are performed on an outpatient basis in a laser clinic.  As a patient, you will lie on your back on a moveable bed with your head positioned under the laser system (laser, microscope and computer screen).  Your eye will be numbed with a few drops of topical anaesthetic and a lid speculum is placed between your eyelids to hold them open and prevent blinking of the eyes during the procedure.  One eye is done at a time and the eye which is not being treated will be patched to better align the eye being treated.  Both procedures are painless and require 10-15 minutes to perform.

 

Photorefractive Keratectomy (PRK):

In PRK the surgeon first removes the covering layer of the cornea (the epithelium) and then applies the laser energy to the underlying corneal surface.  A red blinking light is used as a fixation target during the laser procedure.  The procedure is divided into 4 or 8 steps as determined by the laser computer with each step lasting from 3 to 12 seconds depending upon your prescription.  Your surgeon will monitor your eye through the microscope at all times.  The eye tracker on the laser will follow your eye and should your gaze shift more than 1.5 mm, the laser will automatically turn off.  A bandage soft contact lens is placed on the cornea at the conclusion of the procedure to promote healing.  The epithelium grows back over 3-4 days and the vision gradually improves once this protective layer has healed.

Removal of the surface corneal epithelium is associated with increased ocular discomfort in the post-operative period, a longer time for vision recovery, and increased incidence of regression (loss of effect - a return of some myopia, hyperopia and/or astigmatism), an increased risk of infection and the potential to develop haze or scarring.
 

Laser In-Situ Keratomileusis (LASIK):

LASIK was conceived to address the drawbacks of PRK.  In the LASIK procedure, a flap of cornea is created using a specialized automated surgical cutting instrument called a microkeratome.  The flap is approximately 30% of the thickness of the cornea.  A suction ring is used to hold the eye and microkeratome in appropriate alignment.  The suction ring, in place during the cutting of the LASIK flap (20-30 seconds), is responsible for the pressure sensation that patients feel and also causes vision to dim and go gray or white.  Once the flap is cut the suction ring is removed and the vision returns.  The corneal flap is then folded back blurring the vision.  You will stare at a red blinking fixation light as your eye is positioned under the laser.  The laser treatment is then commenced.  The laser portion of the treatment is identical to that of PRK.  The corneal flap is then replaced and the natural suction within the cornea keeps the flap in its place.  Vision immediately after LASIK is very blurred (like looking through smoke or water) but clears dramatically in a few hours.  Patients undergoing LASIK are given 10mg of Valium one half hour before the procedure to ensure relaxation. 

The creation of the LASIK flap preserves the surface corneal epithelium and is therefore associated with significantly reduced ocular discomfort, a more rapid visual recovery, reduced regression and no haze.  The intraoperative risks associated with LASIK are greater than with PRK because of the possible complications related to creation of the corneal flap.