Certain vision problems such as nearsightedness, farsightedness and astigmatism can be reduced or eliminated surgically. These vision problems occur when the eye is not able to bring images to a proper focus inside the eye.
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.
In nearsightedness (myopia) the cornea is often too steep and light rays focus in front of the retina. Near vision is clear and distant vision is blurry.
With astigmatism the curve of the cornea is irregular and egg shaped, causing light rays to focus at multiple points and resulting in blurred or double vision at all distances.
In farsightedness (hyperopia) the cornea is often too flat and light rays focus behind the retina. Both near anddistant vision are usually blurry.
Vision correction surgery involves techniques that correct or reduce nearsightedness, farsightedness and astigmatism by reshaping the surface of the cornea. To correct nearsightedness, the curvature of the cornea is flattened; to correct farsightedness, the curvature is increased. Techniques that reduce astigmatism reshape the cornea producing a more evenly curved surface.
RK (radial keratotomy), AK (astigmatic keratotomy), PRK (photo-refractive keratectomy), and LASIK (laser assisted in situ keratomileusis) are the most common vision correction surgery techniques used today.
For over 30 years, a technique called radial keratotomy (RK) has been used to reduce or eliminate low to moderate degrees of nearsightedness and astigmatism in millions of people. Using a hand held diamond blade, microscopic incisions are placed in a spoke-like or curvilinear pattern around the outer portion of the cornea to reshape its curvature. This reshaping allows light rays to focus properly on the retina, reducing or eliminating nearsightedness and astigmatism. The incisions are invisible to the naked eye and the procedure only takes minutes to perform.
There are many lasers used in eye care today, but only one particular laser, the excimer laser, is used for vision correction surgery. Unlike other lasers that produce heat and tend to damage surrounding tissue, the excimer laser mixes gases together to produce a cool, non-thermal beam of light. Guided by a sophisticated computer, this cool laser beam can reshape the curvature of the cornea by removing molecules of tissue without damaging or affecting surrounding tissue. The excimer laser is so precise that each pulse can remove 39 millionths of an inch of tissue in 12 billionths of a second. It would take 200 excimer laser pulses to cut through a human strand of hair.
The excimer laser is used for two primary vision correction surgeries, PRK and LASIK. PRK (photorefractive keratectomy) uses the excimer laser to correct low to moderate degrees of nearsightedness. With PRK, the excimer laser is used to delicately reshape the outer surface of the cornea. While the patient is sitting in a reclined position, the excimer laser can precisely reshape the curvature of the cornea in approximately 40 seconds. This reshaping enables light rays entering the eye to focus properly on the retina, resulting in clearer vision. Since the laser removes only a thin layer of the superficial cornea, the cornea retains its original strength.
LASIK (laser assisted in situ keratomileusis) can be used to treat low to high levels of nearsightedness and astigmatism and low to moderate levels of farsightedness. LASIK combines the precision of the excimer laser with a proven procedure that has been performed manually for over 30 years.
While PRK treats the surface of the cornea, LASIK treats the inner tissue of the cornea. Using an instrument called a microkeratome, a small cap is partially lifted from the very top surface of the cornea and hinged to the side, leaving the inner portion of the cornea exposed.
For nearsightedness and astigmatism, the central portion of the exposed cornea is reshaped with the excimer laser, and for farsightedness, the peripheral portion of the exposed cornea is reshaped with the laser. The cap is then placed back in the original position and due to the cornea's extraordinary natural bonding qualities, the cap remains in position without stitches or sutures.
Vision correction surgery has corrected or improved the vision of millions of people. Studies show that over 95% of patients who have had vision correction surgery are able to pass a standard driver's license eye exam (20/40 visual acuity or better) without corrective lenses. Although perfect vision with corrective lenses following surgery may be a likely result, not every patient will be able to achieve the ideal 20/20 vision. The goal of vision correction surgery is to provide functional vision. Since perfect vision is not always achievable, some patients may desire to wear corrective lenses after surgery for some activities.
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