Synonyms for emmetropic or Related words with emmetropic
Examples of "emmetropic"
Newborns begin hypermetropic and then undergo a myopic shift to become
Corrective eye surgery such as LASIK and PRK aims to correct anemmetropic vision. This is accomplished by ensuring the curvature of the cornea, the shape of the lens and their distances from each other and the retina are in harmony. By shaping the cornea,
vision can be achieved without corrective lenses. The correction for only
vision is often why patients are still advised to wear glasses to read as they age due to presbyopia.
For an unaccommodated
eye, the far point is at infinity, but for the sake of practicality, infinity is considered to be 6 m because the accommodation change from 6 m to infinity is negligible.
50. LASIK for the correction of presbyopia in
patients using aspheric ablation profiles and a micro-monovision protocol with the Carl Zeiss Meditec MEL80 and VisuMax. Journal of Refractive Surgery. 2012 Aug;28(8):531-541. "Dan Z. Reinstein, Glenn I. Carp, Timothy J. Archer, Marine Gobbe"
Concomitant esotropia – that is, an inward squint that does not vary with the direction of gaze – mostly sets in before 12 months of age (this constitutes 40% of all strabismus cases) or at the age of three or four. Most patients with "early-onset" concomitant esotropia are
, whereas most of the "later-onset" patients are hyperopic. It is the most frequent type of natural strabismus not only in humans, but also in monkeys.
An eye that has no refractive error when viewing distant objects is said to have "emmetropia" or be "
" meaning the eye is in a state in which it can focus parallel rays of light (light from distant objects) on the retina, without using any accommodation. A distant object in this case is defined as an object 8 meters or further away from the eye.
Age and refractive error play a role in determining the onset of PVD in a healthy person. PVD is rare in
people under the age of 40 years, and increases with age to 86% in the 90s. Several studies have found a broad range of incidence of PVD, from 20% of autopsy cases to 57% in a more elderly population of patients (average age was 83.4 years).
Emmetropia (from Greek "emmetros", "well-proportioned" or "fitting", + "-opia") describes the state of vision where a faraway object at infinity is in sharp focus with the eye lens in a neutral or relaxed state. This 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 chart test). For example, on a Snellen chart test,
eyes score at "6/6"(m) or "20/20"(ft) vision, whereas myopic (near-sighted) eyes might score at 20/40 and hyperopic (far-sighted) eyes might score at 20/15.
Acuity is a measure of visual performance and does not relate to the eyeglass prescription required to correct vision. Instead, an eye exam seeks to find the prescription that will provide the best corrected visual performance achievable. The resulting acuity may be greater or less than 6/6 = 1.0. Indeed, a subject diagnosed as having 6/6 vision will often actually have higher visual acuity because, once this standard is attained, the subject is considered to have normal (in the sense of undisturbed) vision and smaller optotypes are not tested.
subjects with 6/6 vision or "better" (20/15, 20/10, etc.), may still require an eyeglass correction for other problems related to the visual system, such as astigmatism, ocular injuries, or presbyopia.
Visual acuity depends upon how accurately light is focused on the retina, the integrity of the eye's neural elements, and the interpretative faculty of the brain. "Normal" visual acuity (in central, i.e. foveal vision) is frequently considered to be what was defined by Herman Snellen as the ability to recognize an optotype when it subtended 5 minutes of arc, that is Snellen's chart 6/6 meter, 20/20 feet, 1.00 decimal or 0.0 logMAR. In young humans, the average visual acuity of a healthy,
eye (or ametropic eye with correction) is approximately 6/5 to 6/4, so "it is inaccurate to refer to 6/6 visual acuity as "perfect" vision". 6/6 is the visual acuity needed to discriminate two contours separated by 1 arc minute- 1.75 mm at 6 meters. This is because a 6/6 letter, E for example, has three limbs and two spaces in between them, giving 5 different detailed areas. The ability to resolve this therefore requires 1/5 of the letter's total size, which in this case would be 1 minute (visual angle). The significance of the 6/6 standard can best be thought of as the lower limit of normal or as a screening cutoff. When used as a screening test, subjects that reach this level need no further investigation, even though the average visual acuity with a healthy visual system is typically better.
A-scan ultrasound biometry, commonly referred to as an A-scan (short for Amplitude scan), is routine type of diagnostic test used in optometry or ophthalmology. The A-scan provides data on the length of the eye, which is a major determinant in common sight disorders. The most common use of the A-scan is to determine eye length for calculation of intraocular lens power. Briefly, the total refractive power of the
eye is approximately 60. Of this power, the cornea provides roughly 40 diopters, and the crystalline lens 20 diopters. When a cataract is removed, the lens is replaced by an artificial lens implant. By measuring both the length of the eye (A-scan) and the power of the cornea (keratometry), a simple formula can be used to calculate the power of the intraocular lens needed. There are several different formulas that can be used depending on the actual characteristics of the eye. All the information here is not valid for medical purposes.
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