Laser Eye Surgery

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Refractive Errors The cornea is a part of the eye that helps focus light to create an image on the retina (figure1). It works in much the same way that the lens of a camera focuses light to create an image on film. The bending and focusing of light is also known as refraction. Usually the shape of the cornea and the eye are not perfect and the image on the retina is out-of-focus (blurred) or distorted. These imperfections in the focusing power of the eye are called refractive errors. There are four primary types of refractive errors: myopia, hyperopia, astigmatism and presbyopia. Persons with myopia (figure 2), or nearsightedness, have more difficulty seeing distant objects as clearly as near objects. Persons with hyperopia (figure 3), or farsightedness, have more difficulty seeing near objects as clearly as distant objects. Astigmatism (figure 4) is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye. Combinations of myopia and astigmatism or hyperopia and astigmatism are common. Presbyopia affects people as they enter their 40s. Caused by changes within the eye's crystalline lens as one ages, presbyopia affects everyone, and eventually everyone will need to wear reading glasses or bifocals[i]. Presbyopia is not affected by the laser treatment. Glasses or contact lenses are designed to compensate for the eye's imperfections. Surgical procedures aimed at improving the focusing power of the eye are called refractive surgery. In LASIK surgery, precise and controlled removal of corneal tissue by a special laser reshapes the cornea changing its focusing power. [pic] [pic] Figure 1: Normal eye where image forms on retina[ii] Figure 2: Image forms in front on retina[iii] [pic] [pic] Figure 3: Image forms behind retina[iv] Figure 4: Astigmatism:

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