26 Facts About Visual acuity

Visual acuity commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision.

Visual acuity is dependent on optical and neural factors, i e the sharpness of the retinal image within the eye, the health and functioning of the retina, and the sensitivity of the interpretative faculty of the brain.

Common cause of low visual acuity is refractive error, errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain.

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, Visual acuity can be considered a measure of neural well-functioning.

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Visual acuity is typically measured while fixating, i e as a measure of central vision, for the reason that it is highest in the very center.

Visual acuity is a measure of the spatial resolution of the visual processing system.

Precise distance at which Visual acuity is measured is not important as long as it is sufficiently far away and the size of the optotype on the retina is the same.

Visual acuity is measured by a psychophysical procedure and as such relates the physical characteristics of a stimulus to a subject's percept and their resulting responses.

In many vertebrates, such as cats, where high visual acuity is not a priority, there is a reflecting tapetum layer that gives the photoreceptors a "second chance" to absorb the light, thus improving the ability to see in the dark.

Optical aberrations of the eye that decrease visual acuity are at a maximum when the pupil is largest, which occurs in low-light conditions.

Visual acuity cortex is the part of the cerebral cortex in the posterior part of the brain responsible for processing visual stimuli, called the occipital lobe.

Proper development of normal visual acuity depends on a human or an animal having normal visual input when it is very young.

The decreased acuity is reflected in various abnormalities in cell properties in the visual cortex.

Common causes of decreases in visual acuity are cataracts and scarred corneas, which affect the optical path, diseases that affect the retina, such as macular degeneration and diabetes, diseases affecting the optic pathway to the brain such as tumors and multiple sclerosis, and diseases affecting the visual cortex such as tumors and strokes.

Visual acuity is often measured according to the size of letters viewed on a Snellen chart or the size of other symbols, such as Landolt Cs or the E Chart.

In some countries, Visual acuity is expressed as a vulgar fraction, and in some as a decimal number.

When visual acuity is below the largest optotype on the chart, the reading distance is reduced until the patient can read it.

Visual acuity measurement involves more than being able to see the optotypes.

Visual acuity is a subjective test meaning that if the patient is unwilling or unable to cooperate, the test cannot be done.

VEP testing of Visual acuity is somewhat similar to preferential looking in using a series of black and white stripes or checkerboard patterns .

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.

The reason visual acuity is very widely used is that it is easily measured, its reduction often indicates some disturbance, and that it often corresponds with the normal daily activities a person can handle, and evaluates their impairment to do them .

Normally, visual acuity refers to the ability to resolve two separated points or lines, but there are other measures of the ability of the visual system to discern spatial differences.

Stereoscopic Visual acuity is the ability to detect differences in depth with the two eyes.

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Motion Visual acuity limit affects radial motion in accordance to its definition, hence the ratio of the velocity to the radius must exceed :.