Performed since the early 1970's, refractive surgery procedures improve vision for people with nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. Laser assisted In-Situ Keratomileusis (LASIK) is an excellent technique for reshaping the surface of the cornea (outer window of the eye) to correct these common vision problems.
Essentially, LASIK removes tissue within the cornea to treat low to high levels of nearsightedness, farsightedness, and astigmatism. In normal vision, light enters the eye through the cornea and is focused at a single point on the retina at the back of the eye.
With a refractive error, there is a defect in the way light passes through the eye. Light rays do not refract (bend) properly to achieve a single focus point. Instead, light rays focus in front of the retina (nearsighted), behind the retina (farsighted), or at two different points (astigmatism). Refractive errors usually result from a defect in the length of the eye or shape of the cornea.
Overview of the corrective laser procedures
You may have heard about PRK, which stands for Photorefractive Keratectomy. PRK and LASIK (Laser in-situ Keratomileusis) both utilize a Laser System to remove corneal tissue in order to flatten the cornea. In PRK, the laser works on the surface of the cornea. With LASIK, we first create a flap on the cornea and then use the laser for treatment below the corneal surface. RK (Radial Keratotomy) is a non-laser procedure where we use a knife to make a series of radial cuts into the corneal surface. These cuts are intended to produce a bulging effect in order to flatten the corneal surface.
Both PRK and LASIK have now been approved by the FDA. Over four million patients worldwide have been treated successfully. The FDA has recognized laser vision correction for nearsightedness, farsightedness, and astigmatism, and found the treatment safe and effective for eligible patients.Because of increased patient comfort (the treatment itself is painless), less chance of haze, and faster recovery times, most of our patients choose LASIK.
LASIK is performed on an outpatient basis using an "eye drop" anesthetic to numb the eye for painless surgery. The procedure normally takes less than 30 minutes and the patient leaves shortly after. After LASIK, patients usually return to their normal lifestyle quickly with very few restrictions during the short healing period.
LASIK uses lasers to correct vision. Lasers use light beams that are made from a single color or wavelength of light and which have all of the light rays traveling in the same direction (coherent light). Laser light is not radiation, as are x-rays, cosmic rays, and gamma rays. The light itself is cool, safe, and does not become effective in medical treatment until it becomes highly concentrated through the use of special mirrors and lenses. Laser light reaches its maximum strength at the focal point, the point where all the rays converge. The strength of the beam rapidly diminishes after passing the focal point, and can no longer affect other tissues in the eye.
The Excimer Laser
Instead of using heat to alter tissues like other lasers, an excimer laser beam breaks the bonds that link tissues together with only minimal effect on surrounding tissues. These unique properties allow the excimer laser to be used in the LASIK procedure to reshape corneal tissue. After LASIK, light rays focus more precisely on the retina.
The LASIK Procedure
A special instrument (a microkeratome) is applied to the cornea, creating a thin flap of corneal tissue. The flap remains attached to the eye at one end. Next, the laser is used to reshape the cornea.
Wavefont technology allows surgeons to perform customized LASIK, LASEK, and other refractive surgeries using information gathered from the patient's own eyes. During a pre-operative examination, light is projected onto the retina and a set of measurements called a wavefront is created. Data obtained from the wavefront exam is converted into a waveprint, a unique profile of the patient's optical system that is as personal as a fingerprint. Using the results of the wavefront procedure, surgeons can correct the particular refractive errors that obscure the patient's vision.
During laser vision correction surgery, laser pulses must be accurately placed to reshape the cornea. A challenge to this procedure is the patient's constant eye movement. A person's eyes make small, involuntary movements known as saccadic movements about 100 times per second. Since the saccadic movements will not stop during the surgery, most excimer laser systems use an eye-tracking device that measures the movements and guides the placement of the laser beam.
VISX™'s CustomVue procedure combines the technologies of the WaveFront and STAR S4 Excimer Laser systems for high-definition, high-accuracy LASIK vision correction. Benefits of the CustomVue process include faster treatment time, elimination of need for pharmacological pupil dilation, minimal heating of the cornea, capability of ignoring errors arising from torsional eye movements, variability of beam size and depth during spot scanning, and individualized treatment with images based on hundreds of data points gathered from each patient's pupil.
An FDA clinical study reports that six months after the VISX CustomVue™ procedure:
-- 100% of participants could pass a driving test without glasses or contacts
-- 94% of participants could see 20/20 or better without glasses or contacts
-- 74% of participants could see better than 20/20 without glasses or contacts.
20/20 is the current standard for excellence in vision. But, with the CustomVue™ procedure, individuals have the potential to see even better than 20/20. In fact, six months after the CustomVue procedure more than 74% percent of clinical study participants saw 20/16 or better. Many patients even found their night vision was improved after this procedure. In fact, in the clinical study, four times as many participants were very satisfied with their night vision after the procedure as compared to their night vision before with glasses or contacts.
PRK or Photo-Refractive Keratectomy treats refractive errors by removing tissue from the surface of the cornea. First, the epithelium, a thin layer of protective skin on the front of the cornea will be removed. Next the Excimer Laser, usually in less than a minute, will remove the proper amount of tissue thus reshaping the surface of the cornea. A bandage contact lens is then placed on the eye for 2 to 3 days until the epithelium heals. Patients often experience discomfort and a watery eye for the first 24-72 hours after their procedure. Vision may take up to three months to stabilize.
Possible risks and complications include infection (very rare and usually treated with eye drops), over or under correction, glare, or post-operative haze.
A computer, programmed by the doctor for each person's own correction factors, controls the laser and the reshaping of the cornea. The procedure is performed while the patient lies on her/his back. In treating myopia the laser segment of the procedure starts with a narrow diameter beam. As the laser beam expands or moves, a tiny lens-shaped disc is created. The focal point of the beam only penetrates the cornea about two-thousandths of an inch (about half the thickness of a human hair). Only a small area in the center of the cornea is treated, essentially producing a concave lens over the visual axis. Finally, the corneal flap is replaced without stitches and the LASIK procedure is complete.
With hyperopia, the shape of the cornea is essentially steepened to allow images to correctly focus on the retina. For astigmatism, the laser beam scans back and forth along the cylindrical axis to reshape the eye.
After LASIK, the majority of people are able to pass a drivers license test without glasses or contacts. Many patients report an immediate improvement within the first day. For others, vision may be blurry during the healing period. Since an individual's situation, healing powers and tissues are unique, not everyone should expect to achieve full visual correction. People with high to severe levels of myopia or astigmatism may require another procedure to achieve the desired results. People with extremely strong glasses for example, may end up with significant correction, but still need mild to moderate strength lenses part of the time for some activities.
Is LASIK for Everyone?
To be eligible for LASIK the eye must be in good health and vision must be stable. However, some people are better candidates than others and consultation with the doctor prior to surgery is important to determine estimated benefits and possible complications.
Reading Glasses after Age 40
As the body matures, about the age of 40, the normally soft, flexible, focusing lens becomes hard and has difficulty focusing on close objects. Reading vision becomes blurred and difficult. Called presbyopia, bifocals and reading glasses, which aid the eye in focusing on close objects, are used to treat this condition. Since the laser has no effect on the lens of the eye and cannot improve vision due to presbyopia, people who have had LASIK and have or develop presbyopia will need reading glasses for small print. However, a procedure called MONOVISION may be used for people with presbyopia that corrects one eye for distance and leaves the other eye corrected for reading.
Mark D. Fromer, M.D., board certified ophthalmologist in surgery and treatment of eye diseases, has the distinction of being the eye surgeon for the New York Rangers hockey team. Dr. Fromer specializes in laser vision correction procedures, lectures extensively throughout the U.S., and maintains a very active role in teaching advanced surgical techniques and laser vision correction surgery to fellow ophthalmologists. Fromer Eye Centers, with three offices in NYC, is one of only four beta sites worldwide for the latest diagnostic software developed by Heidelberg instruments for the early detection and treatment of diabetic macular edema. For more information on this and other forms of advanced vision care, visit http://www.fromereye.com.© 2007 Dr. Mark Fromer
The views and opinions expressed in these articles do not necessarily reflect those of College Central Network, Inc. or its affiliates. Reference to any company, organization, product, or service does not constitute endorsement by College Central Network, Inc., its affiliates or associated companies. The information provided is not intended to replace the advice or guidance of your legal or medical professional.