Editing Refractive error (section)

== Normal refraction ==
In order to see a clear image, the eye must focus rays of light on to the light-sensing part of the eye – the [[retina]], which is located in the back of the eye. This focusing – called [[refraction]] – is performed mainly by the [[cornea]] and the [[Lens (vertebrate anatomy)|lens]], which are located at the front of the eye, the [[Anterior segment of eyeball|anterior segment]].<ref name=":1">{{Cite web |date=2023-04-29 |title=Eye Anatomy: Parts of the Eye and How We See |url=https://www.aao.org/eye-health/anatomy/parts-of-eye |access-date=2023-10-31 |website=[[American Academy of Ophthalmology]] |last1=Boyd |first1=Kierstan |last2=Turbert |first2=David}}</ref>

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. A distant object is defined as an object located beyond 6 meters (20 feet) from the eye.{{cn|date=September 2024}}

When an object is located close to the eye, the rays of light from this object no longer approach the eye parallel to each other. Consequently, the eye must ''increase'' its refractive power to bring those rays of light together on the [[retina]]. This is called [[Accommodation (vertebrate eye)|accommodation]], and is accomplished by the eye thickening the lens.<ref name=":1" />