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 a strong refracting power of the cornea and lens and/or a long axial length of the eye. A nearsighted person sees near objects clearly, while 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 the result of the visual image being focused 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 with the aging process. This results in a gradual decrease in the ability of the eye to focus on objects that are close up. It is usually noticed around the age of 45, when you realize that you need to hold reading materials further away in order to focus on them. Presbyopia occurs progressively in everyone during the aging process.
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.