serraolaser – Pathologies
Vision repair surgery, also called refractive eye surgery, is any surgical procedure used to correct vision problems. In recent years, tremendous advancements have been made in this field. After refractive surgery, many patients report seeing better than they had at any other time in their lives.
An excimer laser is a form of ultraviolet chemical laser which is commonly used in eye surgery and semiconductor manufacturing typically uses a combination of an inert gas (Argon, krypton, or xenon) and a reactive gas (fluorine or chlorine). Under the appropriate conditions of electrical stimulation, a pseudo-molecule called a dimer is created, which can only exist in an energised state and can give rise to laser light in the ultraviolet range. This light is exceptionally well focussed and capable of very delicate control, and is well absorbed by biological matter and organic compounds. These properties make excimer lasers well suited to precision micromachining organic material (including certain polymers and plastics), or delicate surgeries such as eye surgery (LASIK).
Rather than burning or cutting material, the excimer laser adds enough energy to disrupt the molecular bonds of the surface tissue, which effectively disintegrates into the air in a tightly controlled manner through ablation rather than burning. Thus excimer lasers have the useful property that they can remove exceptionally fine layers of surface material with almost no heating or change to the remainder of the material which is left intact.
The first excimer laser was invented in 1971 by Nikolai Basov, V. A. Danilychev and Yu. M. Popov, at the P. N. Lebedev Physical Institute in Moscow, using a xenon dimer (Xe2) excited by an electron beam to give stimulated emission at 172 nm wavelength. A later improvement was the use of noble gas halides (originally XeBr), invented (and patented) in 1975 by George Hart and Stuart Searles of the United States Government’s Naval Research Laboratory.
In 1980 – 1983, Dr. Samuel Blum was working with Dr. Rangaswamy Srinivasan and James Wynne at IBM’s T. J. Watson Research Center when they observed the effect of the ultraviolet excimer laser on biological materials. Intrigued, they investigated further, finding that the laser made clean, precise cuts that would be ideal for delicate surgeries. For their work, they were awarded patent #4,784,135 and Dr. Blum and Dr. Rangaswamy Srinivasan were elected to the National Inventors Hall of Fame in 2002.
All vision correction surgeries work by reshaping the cornea, or clear front part of the eye, so that light traveling through it is properly focused onto the retina located in the back of the eye. There are a number of different surgical procedures used to reshape the cornea, including:
LASIK: Short for laser in-situ keratomileusis, this procedure is used to correct vision in people who are nearsighted, farsighted, and/or have astigmatism. During LASIK, vision is corrected by reshaping underlying corneal tissue so that it can properly focus light into the eye and onto the retina. This procedure differs from others in that a flap is made in the outer layer of the cornea so that the underlying tissue can be accessed.
PRK: Short for photorefractive keratectomy, this procedure is used to correct mild to moderate nearsightedness, farsightedness, and/or astigmatism. During PRK, an eye surgeon uses a laser to reshape the cornea. This laser, which delivers a cool pulsing beam of ultraviolet light, is used on the surface of the cornea not underneath the cornea, like in LASIK. Therefore, no cutting is required.
LASEK: Short for laser epithelial keratomileusis, this is a newer form of laser vision correction that combines many of the benefits of LASIK and PRK. However, unlike LASIK and PRK, there is no cutting or scraping of the eye, instead an epitheal flap is created using a 20% alcohol solution. It is used to treat nearsightedness, farsightedness, and astigmatism.
ALK: Short for automated lamellar keratoplasty, this procedure is used to correct vision in people with severe nearsightedness and slight degrees of farsightedness. As in LASIK, a flap is created in the cornea so that the doctor can reach the underlying tissue. However, during this procedure, a laser is not used to correct vision. Instead, another incision is made on the sub layer of the cornea to reshape the cornea.
LTK: Short for laser thermokeratoplasty, this is a new procedure used to treat farsightedness and astigmatism. During the procedure a laser beam uses heat to shrink and reshape the cornea. Vision is corrected in a matter of seconds, without any cutting or removal of tissue.
AK: Short for astigmatic keratotomy, this is a surgical procedure used to correct astigmatism. The cornea of people who have astigmatism is shaped like a football. AK corrects astigmatism by making one or two incisions at the steepest part of the cornea. These incision(s) cause the cornea to relax and take a more rounded shape. This procedure may be used alone, or in combination with other vision repair procedures such as PRK, LASIK, or RK.
RK: Short for radial keratotomy, this procedure was once one of the most frequently used surgical procedures to correct nearsightedness. However, since the development of more effective vision repair procedures, such as LASIK and PRK, RK is rarely used today.
Are these procedures safe and effective?
While the results of corrective surgeries have been promising, there are possible side effects. It is important to keep these side effects in mind when considering vision correction surgery.
- Infection and delayed healing: Infection resulting from PRK occurs in one-tenth of one percent of patients. For LASIK, this number is even smaller. If an infection does result from surgery, it generally means added discomfort and a longer healing process.
- Undercorrection or overcorrection: It is difficult to accurately predict the success of eye surgery until the eye has healed properly. Patients may still need to wear corrective lenses even after surgery. Often surgeries resulting in undercorrections can be adjusted with a secon surgery.
- Worse vision: Occasionally the vision through corrective lenses is actually worse after the surgery than it was before surgery. This may be a result of irregular tissue removal or excess corneal haze.
- Excess corneal haze: Corneal haze occurs as a part of the natural healing process after some of these procedures, including PRK. It usually has no effect on the final outcome of vision after surgery and can only be seen through an eye examination. Occasionally, however, this haze may affect a patient’s vision. A second surgery may be needed to correct it. The risk of corneal haze is much less with LASIK than it is with PRK.
- Regression: Sometimes the effects of surgery gradually disappear over a period of several months. When this happens a second surgery is often recommended to achieve permanent results.
- Halo effect: The halo effect is an optical effect that occurs in dim light. As the pupil enlarges, the untreated area on the outside of the cornea produces a second image. Occurring sometimes in patients having LASIK or PRK, this can affect and interfere with night driving, especially in patients who have big pupils in dark conditions.
- Flap damage or loss: This is a risk factor with the LASIK procedure only. Instead of creating a hinged flap on the central cornea that can be closed, the entire flap may detach, risking permanent damage to the cornea.
Refractive surgeries require healthy eyes that are free from retinal problems, corneal scars, and any eye disease. Beyond side effects, there are other questions to ask before deciding on refractive surgery, such as:
- Will your insurance cover the cost?
- How long will recovery take?
- Will there be any activity restrictions after surgery?
As technology progresses more and more, it is very important that you explore all options and possibilities before deciding which vision repair treatment is right for you.