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Refractive Error

A defect in the focusing of light on the retina.

PubMed Health Glossary
(Source: NIH - National Cancer Institute)

About Refractive Errors

Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina. The length of the eyeball (longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors.

What is refraction?

Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see.

What are the different types of refractive errors?

The most common types of refractive errors are myopia, hyperopia, presbyopia, and astigmatism.

More about Refractive Errors NIH - National Eye Institute

What works? Research summarized

Evidence reviews

Screening school aged children and adolescents for reduced vision caused by the need for glasses

Worldwide, the leading cause of reduced vision in children is an unidentified need for them to wear glasses. The reduced vision that results from abnormal focusing (refractive error) can cause the children to screw up their eyes and complain of headaches. Reduced vision may affect academic performance, choice of occupation and socio‐economic status in adult life. Genetic and environmental factors are known to affect the development of refractive error; it is also more common in certain racial groups. Short sightedness has become the commonest eye condition. The need to correct refractive error is determined by its effect on vision. Normal vision can usually be restored by wearing corrective glasses or contact lenses. However, there is some evidence that correction may cause an error to persist where it might otherwise have resolved or reduced naturally. Vision screening is used widely but is concentrated in developed countries; in developing countries it may serve the purpose of providing access to health care. The value of screening after school entry has been queried. Programmes vary with regard to testing personnel, set threshold for failure, frequency and setting. The disability caused by a vision deficit has not been quantified and the optimum age and number of occasions for screening have not been established. The aim of this review was to find studies that evaluated the effectiveness of school vision screening programmes in first identifying children with reduced vision. No eligible randomised studies were found. There is a clear need for reliable evidence to measure the effectiveness of vision screening. A narrative synthesis of other retrieved studies was undertaken in order to explain current practice.

Treatment for lazy eye caused by a need for glasses

Children who have amblyopia due to a need for glasses in one eye only are often asked to wear a patch over the good eye, in addition to wearing their spectacles, to improve their vision. This review found that for some children with this type of amblyopia a period of glasses wear alone can restore normal vision. For those children for whom glasses wear alone does not improve vision there is evidence that wearing a patch can further improve vision. At present it is not possible to tell at the start of treatment which children will respond to glasses alone and which ones will need a patch as well. The amount of patching needed for an individual child cannot yet be predicted. This is because the effects of factors such as age are not fully understood. These findings are based on the results of eleven high‐quality trials.

Glaucoma: Diagnosis and Management of Chronic Open Angle Glaucoma and Ocular Hypertension

This guideline covers adults (18 and older) with a diagnosis of chronic open angle glaucoma or ocular hypertension and those with chronic open angle glaucoma or ocular hypertension associated with pseudoexfoliation or pigment dispersion. In addition, the guideline will cover populations who have a higher prevalence of glaucoma and may have worse clinical outcomes including people with a family history of glaucoma, younger people (<50 years) and people who are of black African or black Caribbean descent. Options for pharmacological, surgical, laser and complimentary or alternative treatments are considered in terms of clinical effectiveness and cost effectiveness.

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Summaries for consumers

Screening school aged children and adolescents for reduced vision caused by the need for glasses

Worldwide, the leading cause of reduced vision in children is an unidentified need for them to wear glasses. The reduced vision that results from abnormal focusing (refractive error) can cause the children to screw up their eyes and complain of headaches. Reduced vision may affect academic performance, choice of occupation and socio‐economic status in adult life. Genetic and environmental factors are known to affect the development of refractive error; it is also more common in certain racial groups. Short sightedness has become the commonest eye condition. The need to correct refractive error is determined by its effect on vision. Normal vision can usually be restored by wearing corrective glasses or contact lenses. However, there is some evidence that correction may cause an error to persist where it might otherwise have resolved or reduced naturally. Vision screening is used widely but is concentrated in developed countries; in developing countries it may serve the purpose of providing access to health care. The value of screening after school entry has been queried. Programmes vary with regard to testing personnel, set threshold for failure, frequency and setting. The disability caused by a vision deficit has not been quantified and the optimum age and number of occasions for screening have not been established. The aim of this review was to find studies that evaluated the effectiveness of school vision screening programmes in first identifying children with reduced vision. No eligible randomised studies were found. There is a clear need for reliable evidence to measure the effectiveness of vision screening. A narrative synthesis of other retrieved studies was undertaken in order to explain current practice.

Treatment for lazy eye caused by a need for glasses

Children who have amblyopia due to a need for glasses in one eye only are often asked to wear a patch over the good eye, in addition to wearing their spectacles, to improve their vision. This review found that for some children with this type of amblyopia a period of glasses wear alone can restore normal vision. For those children for whom glasses wear alone does not improve vision there is evidence that wearing a patch can further improve vision. At present it is not possible to tell at the start of treatment which children will respond to glasses alone and which ones will need a patch as well. The amount of patching needed for an individual child cannot yet be predicted. This is because the effects of factors such as age are not fully understood. These findings are based on the results of eleven high‐quality trials.

Amblyopia in children: Overview

In some children one eye is favored by the brain because it provides a better image. If this happens, the other eye is neglected from childhood on, and it does not get the chance to fully develop. This is known as amblyopia or “lazy eye.”

See all (13)

Terms to know

Astigmatism
A disorder of the vision, usually due to a misshapen cornea, such that light does not focus correctly on the retina causing a blurred image.
Cornea
The transparent part of the eye that covers the iris and the pupil and allows light to enter the inside.
Farsightedness (Hyperopia)
A disorder of the vision where the eye focuses images behind the retina instead of on it, so that distant objects can be seen better than near objects.
Lens
Nearsightedness (Myopia)
The condition in which the individual does not see far distances clearly.
Presbyopia
Presbyopia is a slow loss of ability to see close objects or small print. It is normal to have this as you get older. People with presbyopia often have headaches or strained, tired eyes. Reading glasses usually fix the problem.
Retina
The light-sensitive tissue lining at the back of the eye. The retina converts light into electrical impulses that are sent to the brain through the optic nerve.

More about Refractive Error

Photo of a young adult

See Also: Comprehensive Dilated Eye Examination

Other terms to know: See all 7
Astigmatism, Cornea, Farsightedness (Hyperopia)

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