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LASIK, which stands for Laser Assisted In-Situ Keratomileusis, is currently the most commonly performed type of laser vision correction. LASIK eye surgery is a safe and effective treatment for a spectrum of frequent vision problems.
The LASIK procedure involves two steps designed to permanently alter the shape of the cornea, the transparent tissue covering the front of the eye.
First, the LASIK surgeon must create a thin flap near the surface of the cornea. Traditionally this step was done by using a microkeratome, however recent technology allows our doctor to create the flap using the precision of a laser. This technology, called IntraLase, is quickly becoming the preferred method of creating a flap. Once a flap is created, it is gently lifted to grant access to the corneal tissue underneath.
The second step involves using an excimer laser to reshape the cornea. The laser ablates, or removes, predetermined amounts of tissue from the center of the corneal stroma. New custom technology allows more precision in the laser pattern and for those who qualify it is the preferred method. The surgeon then carefully replaces the flap to complete the LASIK procedure.
LASIK eye surgery is a quick and typically painless procedure. For most patients, LASIK surgery improves the vision enough to eliminate the need for corrective lenses. However, it is important that LASIK candidates understand that all surgeries entail a certain amount of risk. Patients should be counseled on the potential risks and benefits of LASIK, then make an informed decision. It is also important for those who undergo LASIK eye surgery to have realistic expectations regarding the results of the procedure.
The eye works in a similar fashion as a camera. Incoming light enters the eyeball through the transparent cornea. As they pass through the cornea, rays of light are bent. This is known as refraction. This refracted light then goes through the pupil and the lens. The lens fine-tunes the light, so that it focuses on the retina. The retina reacts to the light, sending electrical impulses to the brain via the optical nerve. The brain interprets these signals and creates an image.
In people with a refractive error, the light does not focus properly on the retina. One solution to this problem is to have refractive surgery. Laser vision correction procedures like LASIK eye surgery involve using a laser to reshape the cornea so that light focuses onto the retina correctly. Eyes that may have had a focal point in front or behind the retina can be adjusted, resulting in much clearer vision. Although no refractive surgery procedure guarantees 20/20 vision, the vast majority of patients show dramatic eyesight improvement.
Myopia - nearsightedness
Experts agree the most widespread vision problem is myopia. In some parts of the world, the incidence of nearsightedness is close to fifty percent. In the United States alone, as many as seventy million people are believed to be afflicted with myopia. Additional estimates by the National Institutes of Health report that as many as one adult in four suffers from myopia.
An ordinary eyeball is a perfect sphere, and the cornea and lens act to focus incoming light onto the retina, the back inside surface of the eye. In myopic – or nearsighted – patients, the curvature of the cornea is too steep for the shape of the eye. Inbound light is focused in front of the retina, causing distant objects to appear blurry.
To learn how LASIK eye surgery can correct myopia, contact Shiley Eye Center.
Hyperopia - farsightedness
Farsightedness, also known as hyperopia, causes light to focus at a point beyond the retina, resulting in blurry vision. This condition results from an eye that is shorter than normal, or a cornea that is flatter than normal. Nearby objects appear out of focus for these patients, while distant images appear more clear. Hyperopia is different from presbyopia, the difficulty one experiences reading as part of the aging process. Depending on the degree of refractive error, some people with hyperopia may be candidates for LASIK surgery.
To find out if your hyperopia can be corrected through LASIK, contact our office in San Diego, California.
What is astigmatism?
In a person with astigmatism, the cornea has an oblong shape, oval rather than circular. This causes light entering the eye to focus on multiple points rather than one. LASIK eye surgery can accommodate people with astigmatism, so that they too can enjoy clear, comfortable vision.
If you suffer from astigmatism, contact us to see if LASIK eye surgery is the solution for you.
Presbyopia refers to the loss of close up vision associated with getting older. This happens because the protein composition of the lens changes over time, becoming less flexible. As the lens hardens, it makes it more difficult for the eye to focus on objects up close. Presbyopia usually starts between the ages of forty and fifty and continues to progress until approximately sixty-five. This may cause some people who already wear glasses to switch to bifocals. Those who never needed glasses previously, may require ones for reading.
It is important to realize that LASIK eye surgery does not affect the eye's lens, so it cannot be uses to treat presbyopia. So, if you only need reading glasses, refractive surgery is unlikely to be of any help.
Monovision - The LASIK strategy to compensate for presbyopia
Monovision is a strategy in which one eye is corrected for distance vision and one is corrected for near vision. Because monovision breaks with traditional concepts of binocular vision by creating two eyes with unequal correction, skepticism and controversy have surrounded this approach since its inception. Monovision was first described 40 years ago. However, monovision achieved by LASIK surgery has seen dramatically higher percentages of patient satisfaction in the last three years. A recent study performed in 1999, demonstrated an 86% satisfaction rate.
In general, the dominant eye is corrected for distance and the nondominant eye is corrected for near. Strong sighting preference reduces the success of monovision.
The findings of this study indicate that monovision following LASIK is an excellent option for patients older than 40 years. Patient selection and patient education are critical elements in monovision success. When counseling patients preoperatively, it is important to consider occupation, sports, hobbies, and the need to maintain uncorrected near vision.
The results demonstrate that women chose monovision two to one over men, which was statistically significant at the highest confidence level. The primary reason is freedom from glasses for both distance and near. This benefit is reduced by considerations of occupational need, sports, hobbies, and depth perception. Monovision is not recommended for law enforcement officers, airplane pilots, and truck or taxi drivers. While monovision LASIK is more ambitious, requiring careful patient selection and counseling, it can offer excellent visual outcomes for both distance and near. At present, monovision LASIK is the best surgical option to manage presbyopia.
If you are interested in LASIK monovision treatment, contact the Shiley Eye Center.
What Is Refraction?
When light reaches an angled surface it will bend. Convex surfaces bend light toward the center, and concave surfaces bend light away form the center. This phenomenon of bending light is called refraction. Your eye has many different angles that refract light to focus on the retina in the back of your eye.
In a perfect eye, the cornea refracts about 80% of light onto the crystalline lens. The crystalline lens then refracts about 20% onto the retina. If light does not refract onto the retina correctly, a person may suffer from near or far-sightedness. This problem is called a refractive error.
How does the laser work?
Some patients wonder how a laser can correct their vision. The primary function of the laser in LASIK eye surgery is to ablate or remove corneal tissue, thus altering the shape of the cornea, and changing the refraction of light as it passes through. In myopic patients, the curvature of the cornea is flattened. For hyperopic patients, the laser is used to steepen the curvature of the cornea. In essence, the laser is used to reshape the front surface of the cornea. To reach the stroma (the portion of the cornea that is shaped), the corneal epithelium must be removed (as in PRK) or a flap must be created (as in LASIK). A corneal flap can be created using a microkeratome or a special laser.
A number of lasers can be used to perform different types eye surgery. The Argon laser heats tissue and can be used to treat glaucoma and diabetic retinopathy. YAG lasers create a shock wave, which breaks tissue bonds. They can be used to treat some kinds of glaucoma and are sometimes used following cataract surgery.
In laser vision correction, the goal is to alter the shape of the cornea, so that light passing through is properly focused on the retina. An Excimer laser emits a cool, ultraviolet beam (193 nanometers long) that actually vaporizes tissue by breaking carbon-to-carbon bonds. Corneal tissue can removed with phenomenal precision without harming adjacent tissue. Excimer laser vaporization is technically termed photoablation.
The unmatched precision that can be achieved using the Excimer laser makes it the tool of choice for sensitive laser vision correction procedures such as LASIK eye surgery. Each pulse removes approximately 0.25 microns of tissue. This can be compared to slicing 1/200 of a human hair, 1/28 of a red blood cell, or 1/39 millionth of an inch – this is achieved in 4 billionths of a second. This accuracy allows the refractive surgeon to sculpt the cornea gently yet effectively, producing a cornea that properly focuses light onto the retina.
To learn more about the Excimer laser used for LASIK eye surgery, contact us.
Microkeratomes in LASIK Eye Surgery
Jose Barraquer, M.D. from Bogota, Columbia, originally developed the microkeratome, a medical instrument used to make the flap in LASIK surgery. The development and refinement of the microkeratome began in the 1950's and continues to this day. While there are a number of these devices on the market today, all follow the basic design set forth by Dr. Barraquer, who is recognized as the father of refractive surgery.
Microkeratomes work in a fashion similar to that of a carpenter's plane. All of the latest designs feature a suction ring, which is attached to the eye to keep the cornea firm. Microkeratome have a plate that flattens the cornea while an oscillating blade incises the flap at a predetermined depth. Stopping the blade at the appropriate point leaves a hinge.
There have been a number of attempts to improve upon Dr. Barraquer's original microkeratome design. Some newer versions use high-speed gas motors that produce smoother flaps more consistently. Although it is believed that smoother flaps produce better results, this has not been proven in any scientific paper. Some microkeratome manufacturers are developing disposables. These may prove to be the wave of the future, however clinical experience with disposable microkeratomes has been limited. There have also been some ideas advanced regarding flap placement, but clinical experience has yet to prove these alternate techniques are superior.
The laboratory at the Shiley Eye Center in La Jolla, has been involved in many of these microkeratome developments. Due to the Center's involvement in initial clinical testing, the best microkeratome designs are available at our refractive surgery facility near the University of California at San Diego.
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