WordNet
n. sharpness of vision; the visual ability to resolve fine detail (usually measured by a Snellen chart) [syn: acuity, sharp-sightedness]
Wikipedia
Visual acuity (VA) commonly refers to the clarity of vision. Visual acuity is dependent on optical and neural factors, i.e., (i) the sharpness of the retinal focus within the eye, (ii) the health and functioning of the retina, and (iii) the sensitivity of the interpretative faculty of the brain.
A common cause of low visual acuity is refractive error (ametropia), or errors in how the light is refracted in the eyeball. Causes of refractive errors include aberrations in the shape of the eyeball, the shape of the cornea, and reduced flexibility of the lens. In the case of pseudomyopia, the aberrations are caused by muscle spasms. Too high or too low refractive error (in relation to the length of the eyeball) is the cause of nearsightedness (myopia) or farsightedness (hyperopia) (normal refractive status is referred to as emmetropia). Other optical causes are astigmatism or more complex corneal irregularities. These anomalies can mostly be corrected by optical means (such as eyeglasses, contact lenses, laser surgery, etc.).
Neural factors that limit acuity are located in the retina or the brain (or the pathway leading there). Examples for the first are a detached retina and macular degeneration, to name just two. A common impairment amblyopia caused by incorrect nerve pathway function connecting eye with brain is involved. In some cases, low visual acuity is caused by brain damage, such as from traumatic brain injury or stroke. When optical factors are corrected for, acuity can be considered a measure of neural well-functioning.
Visual acuity is typically measured while fixating, i.e. as a measure of central (or foveal) vision, for the reason that it is highest there. However, acuity in peripheral vision can be of equal (or sometimes higher) importance in everyday life. Acuity declines towards the periphery in an inverse-linear (i.e. hyperbolic) fashion.
Usage examples of "visual acuity".
In order for us to see two separate objects actually as two and ijot have them blur together into one object (and this is what is meant by visual acuity), the light from the two objects would have to fall upon two separate photoreceptors with at least one unstimulated photoreceptor in between.
So there you have a three-step process -- increased visual acuity means increased success at getting food, further doses of psilocybin mean more sexual activity with more instances of successful impregnation and birthing of offspring and, finally, contact with the language-catalysing psychedelic tremendum that even for people as sophisticated as ourselves looms as the most tremendous, shocking and challenging mystery in our world.
But, so far as Adrian could telleven with the visual acuity Center gave himDemansk's expression never changed at all.
Dinosaurs have excellent visual acuity, but they have a basic amphibian visual system: it's attuned to movement.
Optical concerns were seeking species with innate visual acuity, and acoustical concerns sought species with expanded ranges of hearing.
Blueberries had been fed to fighter pilots during World War II, they were filled with an enzyme that temporarily increased visual acuity.
Center's visual acuity gave Adrian a degree of accuracy which was far greater than that of any normal slinger, even an expert one.
Poor reading and writing skills are due to fundamental differences in visual acuity –.
Here, visual acuity is not so sharp, nor is our ability to judge distances so good.