Difference between revisions of Emmetropia

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{{For|corrective lenses used to get someone to 20/20 vision|20/20 correction}}
{{For|corrective lenses used to get someone to 20/20 vision|20/20 correction}}
'''Emmetropia''' is the zero [[refractive state]] in which an eye is neither [[nearsighted]] nor [[farsighted]] nor [[astigmatism|astigmatic]]. This causes the [[natural focal plane]] to be [[full correction]]. An eye is said to be emmetropic when the image of an object at infinity (parallel light rays) forms on the [[retina]], rather than in front of or behind it, implying it is also free of [[astigmatism]].
'''Emmetropia''' is the zero [[refractive state]] in which an eye is neither [[nearsighted]], [[farsighted]], nor [[astigmatism|astigmatic]]. This causes the [[natural focal plane]] to be [[full correction]]. An eye is said to be emmetropic when the image of an object at infinity (parallel light rays) forms on the [[retina]], rather than in front of or behind it, implying it is also free of [[astigmatism]].


Babies are born [[farsighted]], and become emmetropic over time after birth through [[axial elongation]] during emmetropization.
Babies are born [[farsighted]], and become emmetropic over time after birth through [[axial elongation]] during emmetropization.

Latest revision as of 17:53, 9 March 2022

Emmetropia is the zero refractive state in which an eye is neither nearsighted, farsighted, nor astigmatic. This causes the natural focal plane to be full correction. An eye is said to be emmetropic when the image of an object at infinity (parallel light rays) forms on the retina, rather than in front of or behind it, implying it is also free of astigmatism.

Babies are born farsighted, and become emmetropic over time after birth through axial elongation during emmetropization.

Thresholds

Eyes are generally regarded as emmetropic if their spherical equivalent is between -0.5 and +0.5 D and can achieve 20/20 distance visual acuity without lenses.

This permits some myopia, hyperopia, and astigmatism. However, a truly emmetropic eye would typically achieve 20/8 acuity (no myopia or astigmatism) and be blurred to 20/20 through a +0.25 lens (no hyperopia).

References