Refractive error is a problem with focusing light accurately on the retina due to the shape of the eye and/or cornea.

Refractive surgery may consist of either permanently changing the shape of the cornea or, alternatively, implanting intraocular lenses.

[3] The Online Mendelian Inheritance in Man (OMIM) database has listed 261 genetic disorders in which myopia is one of the symptoms.

[23] Many genes that have been associated with refractive error are clustered into common biological networks involved in connective tissue growth and extracellular matrix organization.

[22] In studies of the genetic predisposition of refractive error, there is a correlation between environmental factors and the risk of developing myopia.

[23] Additionally, focusing on near objects for long periods of time - such as when reading, looking at close screens, or writing - has been associated with myopia.

This focusing – called refraction – is performed mainly by the cornea and the lens, which are located at the front of the eye, the anterior segment.

[29] When an eye focuses light correctly on to the retina when viewing distant objects, this is called emmetropia or being emmetropic.

This means that the refractive power of the eye matches what is needed to focus parallel rays of light onto the retina.

[32] When refractive errors in children are not treated, the child may be at risk of developing ambylopia, where vision may remain permanently blurry.

[33] Because young children typically do not complain of blurry vision, the American Academy of Pediatrics recommends that children have yearly vision screening starting at three years old so that unknown refractive errors or other ophthalmic conditions can be found and treated if deemed necessary by healthcare professionals.

[33][34] The management of refractive error is done post-diagnosis of the condition by either optometrists, ophthalmologists, refractionists, or ophthalmic medical practitioners.

Those who possess mild amounts of refractive error may elect to leave the condition uncorrected, particularly if the person is asymptomatic.

Eyeglasses work as an added lens of the eye serving to bend the light to bring it to focus on the retina.

[citation needed] If redness, itching, and difficulty in vision develops, the use of the lenses should be stopped immediately and the consultation of ophthalmologists may be sought.

Full thickness corneal graft may be a final option for patients with advanced kerataconus although currently there is interest in new techniques that involve collagen crosslinking.

[41][42] Strategies being studied to slow worsening include adjusting working conditions, increasing the time children spend outdoors,[23] and special types of contact lenses.

[48] The assessment of refractive error is now done in DALY (Disability Adjusted Life Years) which showed an 8% increase from 1990 to 2019.

[7] Far-sightedness more commonly affects young children, whose eyes have yet to grow to their full length, and the elderly, who have lost the ability to compensate with their accommodation system.