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Q. What is Myopia?
A. Myopia is the medical term for "nearsightedness", a condition wherein the eyes can see close objects but are unable to see distant objects clearly. Compared to the normal eye, a myopic eye is longer from front to back. As a result, light is focused in front of the retina, rather than on the retina, resulting in the perception of a blurred image.
Q. What is Astigmatism?
A. In order to have normal undistorted vision, the cornea should be smooth and spherical or equally curved in all meridians. Some eyes have some degree of astigmatism, or ovalness, to their cornea. Instead of being shaped like a basketball, the astigmatic eye is shaped more like an American football. Therefore, there is distortion or tilting of the images due to asymmetric bending of the light rays. This is sometimes perceived by the individual as a "shadow effect" or a doubling of the image.
Q. What is Hyperopia?
A. Hyperopia is the medical term for "far-sightedness." It is a misnomer, however, in that people do not necessarily see clearly only for far. As opposed to myopia, a hyperopic eye is shorter when compared to a normal eye. This results in light being focused behind the retina causing the perception of a blurred image.
Q. What is Presbyopia?
A. Presbyopia is not an EOR, but rather, an age-related loss of the focusing power for near. It usually sets in as one approaches the age of 40 or thereabouts. Normal and farsighted individuals usually require reading glasses once they reach this age. A presbyopic person with a moderate amount of nearsightedness may need only to remove his corrective spectacles for near work or reading. The Excimer laser does not have any effect on the focusing ability of the eyes. Therefore, it cannot be used to treat presbyopia.
Q. How do we correct errors of refraction?
A. Eyeglasses and contact lenses properly focus the light rays on the retina and thus "correct" EORs. However, as soon as these devices are removed from the eye, the eye is again unable to focus light properly. To permanently correct EORs, the corneal surface must be reshaped: flattened for myopia, steepened for hyperopia, and made more spherical for astigmatism.
Before the advent of Excimer lasers, the option for permanent correction of EORs required incisional surgery in the form of Radial Keratotomy (RK) and Astigmatic Keratotomy (AK).
The effectiveness of these procedures relied on weakening the corneal support to attain the desired change in corneal curvature. This compromised the corneal integrity with a potential danger of ocular rupture following trauma. Furthermore, unpredictability of the attained amount of correction, fluctuation in refraction and impermanence of results were common. These limitations accelerated the development of laser technology for refractive surgery.
Q. What is an Excimer Laser?
A. The Excimer laser is a cold laser which works via photochemical ablation. Unlike other lasers that utilize thermal energy to burn tissue, Excimer lasers make use of an argon-fluoride gas mixture to break the molecular bonds of corneal tissue. As a result, fragments of corneal tissue rapidly expand and are ejected at high speed from the corneal surface. The Excimer laser is computer-controlled, allowing precise removal of tissue to the micron level.
Vision correction by the Excimer laser was approved by the United States Food and Drug Administration (US FDA) in 1995 and is among the most commonly performed outpatient clinical procedures in ophthalmology. Over a million people with myopia (nearsightedness), hyperopia (farsightedness) and astigmatism in over 40 countries worldwide have undergone this procedure and have been enjoying functional vision without glasses and contact lenses ever since. Sight-threatening complications are exceedingly rare. This combination of high success and low complication rates has resulted in exceptional patient satisfaction.
At our Center, we use the Alcon Summit Autonomous LADARVision Excimer laser, which is approved by the US FDA for the correction of nearsightedness (myopia), farsightedness (hyperopia) and astigmatism.
Q. What is Photorefractive Keratectomy (PRK)?
A. In contrast to incisional surgery which works by weakening the corneal structure, PRK corrects myopia and astigmatism by altering the shape of the cornea. Portions of the superficial and middle layers of the cornea corresponding to the degree of myopia and/or astigmatism are photoablated. This alters the curvature of the cornea and allows light rays to properly focus on the retina.
PRK is an out-patient procedure, which takes approximately 5 minutes per eye, but the actual laser exposure lasts less than a minute. It is painless, requiring only topical anesthetic drops. Patients typically regain functional vision in 3 to 7 days.
Q. What is Laser-assisted in situ Keratomilieusis (LASIK)?
A. LASIK works like PRK, except that in LASIK, a special ophthalmic instrument - the microkeratome - is used to create a hinged corneal flap prior to actual photoablation of the underlying corneal tissue. After the laser treatment, the flap is repositioned and adheres spontaneously to the underlying bed. LASIK has been proven to be effective in treating even higher degrees of myopia and astigmatism.
LASIK is also an outpatient procedure that takes 5-7 minutes per eye but the actual laser exposure lasts less than a couple of minutes. However, LASIK requires more technical skill and surgical expertise and is seldom performed by the general eye MD. Because the flap preserves the superficial layer of the cornea, visual recovery and healing are dramatically rapid. Patients regain functional vision in 4 to 12 hours.
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