Eyeglasses remain the most common method of correcting vision for myopia. A concave or "minus" lens causes the incoming light rays to diverge before they reach the cornea.
The cornea, in turn, focuses these divergent light rays directly on the retina, and vision becomes clear once again. In hyperopia a convex or "plus" lens causes incoming light rays to converge and focus misdirected light rays directly on the retina.
Glasses are safe, and usually well tolerated. To correct large myopic refractive errors, glasses may be thick and may reduce the size of the visual image by up to 25%.Contact lenses correct refractive errors much like glasses. Contact lenses rest directly on the cornea. If fitted and used properly, they are effective and relatively safe. However, complications such as allergic reactions, infections, and mechanical injury to the cornea sometimes can occur with the use of hard or soft contact lenses.
Radial Keratotomy (RK) was pioneered in Russia and brought to North America in 1979. Deep (90% of the corneal thickness) radial cuts, like the spokes of a wheel, are made in the cornea. These incisions cause the peripheral cornea to bulge, and the central cornea to flatten, thus correcting the myopia.
RK incisions in the cornea.Photorefractive Keratectomy (PRK) uses an excimer laser to reshape the front surface of the cornea. The outer layer of corneal tissue is removed by hand or by the laser. The excimer laser can be used to remove microscopic layers of tissue from the underlying cornea. The outer layer of corneal tissue grows back in 3-5 days and overall healing occurs within 1-3 months. Complications in PRK are the same as for LASIK, but also include the possibility of delayed healing of the outer layer of corneal tissue and excessive corneal haze.
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