Refractive error basics

Courtesy of wader on Flickr

Courtesy of wader on Flickr

What is a refractive error? With refractive errors, the shape of the eye prevents light from focusing on the retina. Factors include the length of the eyeball (either longer or shorter) or changes in the shape of the cornea or lens.

Myopia, otherwise known as nearsightedness, is a vision condition in which you can see close objects clearly, but objects farther away are blurred. Light is focused in front of the retina.

Hyperopia, or farsightedness, is a vision condition in which distant objects are usually seen clearly, but close objects do not come into proper focus. Light is focused behind the retina.

Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or the curvature of the lens inside the eye. The cornea of a normal eye is curved like a basketball. An eye with astigmatism has a cornea that is curved more like a football, with some areas that are steeper or more rounded than others. This may cause images to appear blurry and stretched out. In astigmatism, light is bent differently and is focused at various locations on the retina.

Presbyopia is an age related condition where there is a gradual loss of the eye’s ability to focus on near objects.

Diagnosis of refractive errors can be made by a comprehensive eye examination. Eye examinations are important for all children and adults, starting at 6 months of age. An eye examination will ensure that you can see clearly and comfortably at all distances and detect conditions that may contribute to eyestrain. If needed, glasses, contact lenses or refractive surgery can provide clear and comfortable vision.

~ Melissa Barnett, OD, FAAO
California Optometric Association

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