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 Myopia (nearsightedness) is a vision condition affecting nearly a third of people in the United States. A myopic eye focuses properly on nearby objects, but distant objects appear blurry. This imbalance typically occurs because the cornea either has an oblong shape or is excessively curved, so that only some of the light entering the eye focuses on the retina. The most common symptom is difficulty seeing objects in the distance, for example a chalkboard or television screen. The condition usually develops before the age of 20.
Hyperopia (farsightedness) occurs when the cornea is too flat or irregularly shaped, causing nearby objects to appear blurry while objects in the distance are clear. Common signs of hyperopia include difficulty maintaining a clear focus on nearby objects, and eyestrain or headache after close work.
 Presbyopia is a natural change in our eyes' ability to focus. It occurs when the soft crystalline lens of the eye starts to harden. This loss of flexibility affects the lens' ability to focus light in the eye, causing nearby objects to look blurry. Presbyopia happens to everyone starting in about our 40s or 50s -- even in patients who have had laser vision correction. The effects of presbyopia can be corrected with glasses or contact lenses, including bifocals and multifocals; multifocal lens implantation, including Crystalens™, ReZoom® and ReSTOR®; conventional surgery; and monovision LASIK. Laser surgeries such as conventional LASIK, PRK and LASIK cannot correct presbyopia because they reshape the cornea rather than treat the lens.
Astigmatism is the term for when the cornea is oblong rather than spherical in shape. This irregular curvature prevents light from focusing properly on the retina. As a result, objects that are close or at a distance may appear blurry or doubled. Astigmatism can cause headaches, eyestrain and fatigue to blurred or distorted vision. Most people have some degree of astigmatism, which often occurs in combination with myopia or hyperopia. Regular astigmatism is found in 30-40% of people who wear glasses.
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