Global InformationEmmetropia information
 | This article needs additional citations for verification. (January 2009) |
| Emmetropia | |
|---|---|
 | |
| Specialty | Ophthalmology |
Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle[1] in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision. A human eye in a state of emmetropia requires no corrective lenses for distance; the vision scores well on a visual acuity test (such as an eye chart test).[2]
While emmetropia implies an absence of myopia, hyperopia, and other optical aberrations such as astigmatism, a less strict definition requires the spherical equivalent to be between -0.5 and +0.5 D and low enough aberrations such that 20/20 vision is achieved without correction.
For example, on a Snellen chart test, emmetropic eyes score at least "6/6"(m) or "20/20"(ft) vision, meaning that at a distance of 20 ft (the first number) they see as well as a "normal" eye at a distance of 20 ft (the second number). Eyes that have enough myopia (near-sighted), hyperopia (far-sighted, excluding latent and facultative hyperopia), or optical aberrations would score worse, e.g. 20/40 (visual acuity of 0.5). Typical emmetropic vision might be 20/15 to 20/10 (visual acuity of 1.3 to 2).[3]
Emmetropes with presbyopia might use lenses for near vision.
- ^ Hall, John E.; Michael E. Hall (2021). Guyton and Hall textbook of medical physiology (14th ed.). Philadelphia. ISBN 978-0-323-59712-8. OCLC 1129099861.
{{cite book}}: CS1 maint: location missing publisher (link) - ^ "Eye test chart". Banton Frameworks. 20 December 2022. Retrieved February 11, 2023.
- ^ "We have found also that the best eyes have a visual acuity which approaches 2, and we can be almost certain that if, with a good illumination, the acuity is only equal to 1, the eye presents defects sufficiently pronounced to be easily established." Physiologic Optics: Dioptrics of the Eye, Functions of the Retina, Ocular Movements and Binocular Vision