Emmetropia is associated with
Correct Answer: Absence of refractive error
Description: Emmetropia (optically normal eye) is a state of refraction when the parallel rays of light coming from infinity are focused at the sensitive layer of the retina with accommodation at rest. At bih, the eyeball is relatively sho and thus most infants are born with +2 to +3 D hypermetropia. This is gradually reduced and by the age of 5 to 7 years usually, the eye becomes emmetropic in a person with absent refractive error. Ametropia (a condition of refractive error), is defined as a state of refraction when the parallel rays of light coming from infinity (with accommodation at rest), are focused either in front or behind the sensitive layer of the retina, in one or both the meridians. The ametropia includes myopia, hypermetropia, and astigmatism. Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the eye lens in a neutral or relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfect vision. A human eye in a state of emmetropia requires no corrective lenses; the vision scores well on a visual acuity test (such as an eye cha test). For example, on a Snellen cha test, emmetropic eyes score at "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). Either myopic (near-sighted) eyes or hyperopic (far-sighted) eyes would score worse, e.g. 20/40 (visual acuity roughly half normal). Exceptionally acute vision (excellent cornea and lens and better than standard retina) might be 20/15 Emmetropia is the state of the eye in which no refractive error is present, there is no need for glasses or contact lenses. In emmetropia, the curvature of the cornea, the shape of the lens and their distances from each other all work together to focus the rays of light to create a sharp image on the retina Reference : Khurana comprehensive ophthalmology; 4th edition; P: 28,29
Category:
Ophthalmology
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