ht 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 procedure, 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 centra...
