A Refractive Error is a very common eye disorder that occurs when the eye cannot clearly focus on an image. Refractive errors cause blurry vision, but can be easily corrected with glasses, contact lenses and/or refractive surgery. While refractive errors cannot be prevented, it is important that they are diagnosed and corrected to help patients achieve clear vision.
The four most common types of refractive error are described below.
Nearsightedness (Myopia) is a form of refractive error that focuses light in front of the retina, rather than on the retina. This can be due to too strong of a focusing power of the eye and/or a long length of the eye. A nearsighted person sees near objects clearly, but objects in the distance are blurred. Myopia frequently develops in school-aged children and teenagers and progresses during the growing years. When the growth of the eye is complete, usually by early adulthood, the myopia stabilizes. Myopia can be corrected with glasses, contact lenses and refractive eye surgery (LASIK and PRK).
Farsightedness (Hyperopia) is form of a refractive error that focuses light behind the retina, rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak. Farsightedness is often present from birth, but children can often tolerate moderate amounts without difficulty and most outgrow the condition. As aging occurs, glasses or contact lenses may be required to correct the vision. A family history of farsightedness is a risk factor.
Presbyopia is the age-associated progressive loss of the focusing power of the lens, resulting in difficulty seeing objects close to the eye. The focusing power of the eye, which depends upon the inherent elasticity of the lens, is gradually lost as the eye ages. This results in decreased ability of the eye to change depths of focus. Symptoms of presbyopia usually begin around age 45. Reading glasses, new intraocular lens technologies (that can be implanted during cataract surgery) and even some eye drops can be used to help with symptoms of presbyopia.
Astigmatism is a type of refractive error in which the cornea of the eye is asymmetrically curved, causing out-of-focus vision. The image does not focus on the retina in a sharp point. The cause of astigmatism is unknown. It is usually present from birth, and often occurs together with nearsightedness or farsightedness. A minor degree of astigmatism is considered normal and does not require correction. Astigmatism is very common and can be fixed with glasses, contacts or refractive surgery.