Refractive Errors
Prevent Blindness Mid-Atlantic
Edward H. Titmus, Jr. Center for Sight | 11618 Busy Street | Richmond, VA 23236
(804) 423-2020 | toll-free (888) 790-2020 | fax (804) 423-5409
www.TheEyeSite.org
Washington Area Office | 225 Reinekers Lane, Suite 700 | Alexandria, VA 22314
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A refractive error is a defect in the optics of the eye that results in a lack of precise focus of the light rays of the retina, causing a blurred image.
Light rays entering the eye cannot be brought to a single focus. Instead they may focus in front of, in back of, or irregularly on the retina.
Astigmatism
Astigmatism is a refractive error. The curvature of the cornea and/or lens prevents light rays from focusing on a single point on the retina, resulting in a blurred image.
Visual acuity is poor for near and far objects.
Astigmatism is an overall inability of the eye to focus clearly at any distance, usually because of uneven curvatures of the cornea. Essentially, the cornea is oval, having a surface shaped more like a football or the back of a spoon, rather than being rounded like a basketball.
Virtually all corneas have at least a mild degree of astigmatism. For many, the resulting distortion is not discernible. But as the curvature of the cornea becomes more uneven, image distortion increases.
Astigmatism often is inherited.
Hyperopia (Farsightedness)
Hyperopia is a refractive error. Hyperopia occurs when the eyeball is too short. The reduced length means the point of focus lies beyond the back wall of the eye, and light rays are not yet in focus when they arrive at the retina.
Hyperopic or farsighted people generally can see distant objects clearly, but near objects are out of focus. In more severe cases of hyperopia, even distant objects can be blurred.
Hyperopia usually exists in infancy – as the child grows, so does the size of the eye. Most children lose much of their hyperopia by the time they are teenagers.
Despite having hyperopia, most children can see well at all distances because the accommodation provided by the lens is enough to counteract minor refractive errors.
Myopia (Nearsightedness)
Myopia is a refractive error. Myopic or nearsighted people generally can see near objects clearly, but distant objects are out of focus.
This is the result of a refractive error of the eye in which the image of a distant object is formed in front of the retina and cannot be seen distinctly; near objects are seen more clearly than distant objects.
Myopia is thought to be primarily hereditary in nature.
Myopia, the most common refractive error, affects more than 25 percent of the population.
Myopia usually becomes evident in children between the ages of 8 and 12 and worsens until early adulthood.
Myopia is rare in infants and toddlers.
Myopia that starts in infancy can be more severe than in school-age children.
