Tuesday, April 21, 2020

Seeing Well Without Contact Lenses And Glasses Is The Dream Of Million

Seeing well without contact lenses and glasses is the dream of millions of Americans and modern medical science has enabled that dream to come true (Caster, 8). Since first grade, Dede Head, a 30-year-old fitness trainer in North Carolina, has worn glasses to correct sever nearsightedness and astigmatism. Over the years she became accustomed to wearing glasses and contacts, but this has limited many important aspects of her life, including sports. She then heard of a laser eye surgery that "supposedly", helped to correct a person's vision by means of lasers. She immediately signed up for the procedure and ever since that day, she has not worn glasses or contacts. Dede is just one of the eight hundred-fifty-thousand people who have undergone a procedure by the name of LASIK or Laser In-Situ Keratomileusis. If surgical procedures were movies, LASIK would be this years box office smash as it has received much media coverage and many praises; however, not that many people know what LASIK is, what the advantages and disadvantages are, and most importantly if LASIK is right for them (Buratto, 1). LASIK is basically a type of laser surgery which can help correct nearsightedness (myopia), which is the inability to see distant objects, farsightnedness (hyperopia), which is the inability to see close, and astigmatism, the inability to focus light waves evenly. LASIK has grown greatly in the last year, mostly because of 4 reasons; it is fast (procedure takes about 5-10 minutes), safe, painless, and the results are almost always prolific. The eye is just like a camera because it works by focusing light waves that pass through it. Light rays that enter the eye must first pass through the most outer layer of the eye called the cornea. The cornea performs 2/3 of the focusing process, the remainder of is then completed by the crystalline lens which further focuses the light on the retina. This requires extreme precision in that the focused light must fall exactly at the level of the retina (Gallo, 126). The retina is a nerve tissue that carpets the inner surface of the eye, much like wallpaper covers all aspects of a wall. The retina converts the light into electrical signals, which are transmitted to the brain by the optic nerve. Just as a camera cannot produce clear photographs of the image if the incoming light is not focused on the film, we cannot produce a clear vision if the cornea and crystalline lens do not focus the light precisely on the retina. This is where LASIK steps in. A laser is a device that creates a very special kind of light energy that is usually invisible to the human eye (Caster, 16). In LASIK, ophthalmologists use a certain type of laser called the excimer. By using invisible ultraviolet light, the excimer is able to break covalent bonds between molecules. What sets excimer aside from other lasers used in medicine is the wavelength used. At one-hundred ninety-three nm (nanometers), excimer lasers remove tissue by breaking the covalent without creating much thermal energy (Slade, 25). This allows for precise removal of tissue with minimal surrounding tissue damage. The very thin layer of the cornea that is removed, changes the curvature of the cornea ever so slightly, thus then results in a change in the light focusing ability. In nearsightedness (myopia), light rays from distant objects are not focused on the retina, but instead they are focused in front of the retina (See Figure 1). Therefore to correct nearsightedness in a LASIK procedur e, the curvature of the cornea must be decreased or in another words made flatter by removing corneal tissue in a disc-shaped pattern, or from the central cornea. A computer determines the exact pattern and number of pulses that are needed to do this. In farsightedness (hyperopia), light rays from distant objects are focused not onto the retina, but behind it (See Figure 1). To correct this, the central portion of the cornea must be made steeper; and this is accomplished by removing corneal tissue in a donut shaped pattern, or in another words more from the peripheral areas. Eyes with astigmatisms focus light waves unevenly because of the irregular shape of the cornea; football shaped as opposed

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