Refractive Correction of the Eyes
by: Kathy Miller (11/24/03)
Refractive error is the term used to describe a condition where light entering the eye does not focus directly on the retina therefore producing a blurred image. Light entering the pupil is focused by the bending power of the cornea and lens and directed to the retina. If a sharp focus on the retina is not achieved, a blurred image results.
The common refractive states of the eye are termed myopia, hyperopia, and astigmatism. Myopia (nearsightedness) refers to the condition where light entering the eye is focused in front of the retina. In hyperopia (farsightedness), the image is focused optically behind the retina. In astigmatism, the entire image is not focused at the same point. As an example, one part of the image is focused closer to the image than orthogonal parts. This results in selective blur of parts of the object being viewed. (Refer to the diagram below)
Eye doctors are trained to measure (refract) the eyes to determine the ophthalmic lenses that put a clear focus on the retina. The procedure for measurement is performed in the office by projecting a light into the eye and assessing the reflection of light from the retinal surface. A series of lenses are introduced in front of the eye until the proper retinal focus is achieved. This test may require the instillation of drops prior to testing. Eyeglass prescriptions are based on the results of these measurements.
Significant refractive errors are common in children with vision impairment, but are often overlooked as a means of improving vision. Refractive errors are frequently found in children with retinopathy of prematurity, albinism, chromosome abnormalities and syndromes with retinal degeneration as a feature (i.e., Bardet-Biedl, Alstrom, Cohen syndromes).
There are often challenges faced in achieving compliance with eyeglass wear. Some children are tactile defensive and do not like the feeling of glasses on the face. Others do not recognize the clear benefit glasses provide because the activities they perform may not require glasses. In young children with significant refractive errors however, the concern is to wear the glasses to prevent the possible development of amblyopia (lazy eye).
The appropriate correction with eyeglasses is imperative in maximizing a child's visual performance.
Site
updated:
May 1, 2007
© 2004 The ADVISOR