Laser Vision Correction
The physicians of the Doctors Eye Institute have been involved in refractive surgery since the 1970's. Originally, the shape of the cornea was altered using surgical radial incisions to correct for myopia or near-sightedness. The result was flattening of the central cornea, to bring light rays into focus on the retina. This is known as Radial Keratotomy, and is effective for certain levels of myopia.
More recent techniques for correcting refractive errors utilize the Excimer laser. This laser is unique in the way it reacts with tissues. The light beam from the Excimer laser breaks the bonds that link cells together with only minimal effect on surrounding tissues. In this way, the laser can be used to precisely reshape the surface of the cornea so that light rays come into focus at the retina.
The LASIK and PRK procedures make use of the Excimer laser technology. For each laser procedure, the computer is programmed for the patient's individual correction factors and controls the reshaping of the cornea. In treating myopia with the Excimer laser, for example, an expanding aperture is used so that more tissue is removed from the center of the treated optical zone than from the periphery. Only a small area in the center of the cornea is treated, essentially producing a flattening of the corneal lens over the visual axis. The laser penetrates the cornea about 2 thousandths of an inch. Try the links for more information regarding the specific procedures
To correct nearsightedness, the surgeon makes radial incisions into the cornea, while looking through a high power surgical microscope. The incisions are made in a pattern similar to the spokes on a wheel, with the central optical zone as the hub. The pattern of the incisions is modified to achieve astigmatic correction (AK).
(Automated) Lamellar Keratoplasty ( ALK or LK):
With lamellar keratoplasty a special instrument called a microkeratome is applied to the cornea. This instrument separates the tissue, creating a thin flap of corneal tissue that remains attached to the eye. With hyperopia ( a flat cornea ) the flap is put back into position and the procedure is complete. Normal pressure inside the eye causes the eye to bow increasing the curvature of the cornea. With myopia, a second pass of the microkeratome is made and a thin section of corneal tissue is removed. When the flap is replaced, the curve of the cornea is reduced allowing light rays to focus more precisely on the retina.
Due to presbyopia, myopic people over 40 who choose the refractive surgery to adjust their vision to see distant objects clearly without glasses will probably require glasses for reading. However, one of the procedures described previously may be used to correct one eye for distance and leave the other eye slightly nearsighted for reading. The result is called monovision. Refractive surgery techniques have corrected or improved the vision of hundreds of thousands of people. "Perfect vision" cannot be guaranteed however, and some people are better off staying with corrective lenses. If you are interested in improving your vision without glasses or contacts, a discussion with the doctor and an eye examination will help you decide if refractive surgery is right for you.
Lasik & PRK:
Lasik and PRK are both forms of laser vision correction to reduce refractive errors and reduce or eliminate the need for glasses. In both procedures, the central cornea is reshaped by a precise amount using the Excimer laser. An Excimer laser is a concentrated beam of cool light that can be precisely focused to remove a precise amount of tissue with minimal inflammation or surrounding effect. The laser treatment usually takes less than one minute.
PRK is photo-refractive keratectomy, in which Excimer laser is performed to the surface of the cornea. This means that only the surface epithelium of the cornea needs to be removed. This is effective for low and moderately near-sighted people. Since the surface epithelium has many sensory nerves, there tends to be more pain and tearing as the eye heals following PRK. This is one reason why we use LASIK as the procedure of choice for many patients. LASIK (Laser Assisted In-Situ Keratomileusis) is a procedure for the correction of refractive errors.
LASIK differs from PRK in that a small corneal flap is created with a micro-keratome to allow laser treatment to the deeper part of the cornea. This improves healing time and recovery, and makes for better first day comfort and earlier vision stability since the surface epithelium is not disrupted. As with PRK, the Excimer laser is used to reshape the cornea. Once the laser treatment is completed, the thin corneal flap is laid back into place where it seals to the eye without the need for sutures. With PRK, a contact lens is placed for comfort and to assist healing. We do still recommend PRK for some patients, such as persons with low corrections or certain corneal problems that would make LASIK less safe. In our preliminary examination and consultation, we will perform tests to evaluate your eyes and discuss the treatment recommendations with you.
Many patients want to know how the procedure will feel, what to expect on the day of the treatment:
During the actual procedure, the patient is awake, and the eye is numbed with eye drops. The eye is held open with a spring clip while the patient sits in a reclining chair. Specific refractive information is entered into the computer, and the tissue depth and pattern are calculated. During the actual treatment, the eye is centered as the patient focuses on a small light. The laser then delivers a programmed number of overlapping light pulses, each pulse removing a microscopic layer of the cornea.
With LASIK a few moments are needed to prepare the flap with the microkeratome before the laser treatment. The doctor will check your eyes the following day and usually a week later. Frequent follow up checks are important to ensure normal healing response. Although the vision is often clearer immediately following the procedure, different eyes heal differently. Vision may be blurry at first but it should start to clear in less than 24 hours. We expect maximum improvement in vision in about one month after LASIK. After PRK, vision will be blurry at first, but it should start to clear in three to four days. To protect the cornea as it heals, we recommend using an eye shield at night for two weeks. It's important to use the eye drops as directed and by following a few instructions.
What are the potential risks of LASIK and PRK?
No surgical procedures are without some potential risks. Laser vision correction is no exception. Fortunately, risks are low with LASIK and PRK and serious problems are rare. There is a possibility of over correction or under correction, depending on the healing properties of your cornea. It is possible to repeat or enhance the procedure and this is necessary about 5% of the time.
As with any eye procedures, there is a small risk of infection, which could scar the cornea and decrease vision. Some people experience glare or halos around lights. This is because the edge of the treated zone may come into the edge of the vision axis when the pupils are widely dilated at night. We will measure your pupil sizes to see if you are at particular risk for this. Dry eye condition has been reported among LASIK patients. This is usually temporary, lasting several weeks to months as the corneal flap heals and the nerves regenerate.
Eye drops are usually sufficient to reduce the symptoms of dry eyes following LASIK. With PRK specifically, haze may develop in the cornea a few weeks after surgery. This often clears and responds to treatment. If it does not, vision can be cloudy for months. Only rarely is the haze permanent. LASIK involves the formation of a corneal flap, thus there are some risks associated with this anatomic change. Rarely, inflammation can develop within the flap space, requiring treatment with intensive drops or the flap may heal abnormally, requiring repositioning.
We measure the cornea to ensure that the flap creation will not create a thin cornea, at risk for future thinning. Eye drops themselves have some small risk also. Steroid eye drops can create high pressure in the eye or enhance cataract development. We recommend close follow up, with several visits to ensure that the health of the eye is not compromised, to watch closely for signs of any complications, to treat any problems early to obtain the best possible results for the patient.