Visual acuity definition: Visual acuity (VA) commonly describes the clearness 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 professors of the brain.
What Causes Loss of Visual Acuity?
A typical 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 versatility of the lens. Expensive or too low refractive error (in relation to the length of the eyeball) is the reason for nearsightedness (myopia) or farsightedness (hyperopia) (normal refractive status is described as emmetropia). Other optical causes are astigmatism or more intricate corneal irregularities. These abnormalities can mainly be corrected by optical ways (such as eyeglasses, contact lenses, laser surgery, etc.)
Neural elements that limit acuity are located in the retina or the brain (or the path leading there). Examples for the first are a removed retina and macular degeneration, to call just two. Another common disability, amblyopia, is triggered by the visual brain not having established properly in early childhood. In many cases, low visual acuity is triggered by brain damage, such as from traumatic brain injury or stroke. When optical factors are corrected for, acuity can be considered a procedure of neural well-functioning.
Visual acuity is usually measured while fixating, i.e. as a step of main (or foveal) vision, for the reason that it is highest there. Nevertheless, acuity in peripheral vision can be of equal (or in some cases greater) value in everyday life. Acuity declines to the periphery in an inverse-linear fashion (i.e. the decrease follows a hyperbola).
Visual Acuity Test
The visual acuity test (alsoknown as Eye test – acuity; Vision test – acuity; Snellen test) is used to identify the tiniest letters you can keep reading a standardized chart (Snellen chart) or a card held 20 feet (6 meters) away. Unique charts are used when screening at ranges shorter than 20 feet (6 meters). Some Snellen charts are in fact video screens showing letters or images.
How the Visual Acuity Test Is Performed
This test might be done in a health care service provider’s office, a school, work environment, or in other places.
You will be asked to eliminate your glasses or contact lenses and stand or sit 20 feet (6 meters) from the eye chart. You will keep both eyes open.
You will be asked to cover one eye with the palm of your hand, a paper, or a little paddle while you read out loud the tiniest line of letters you can see on the chart. Numbers, lines, or images are used for people who can not read, particularly children.
If you are not exactly sure of the letter, you may guess. This test is done on each eye, and one at a time. If needed, it is duplicated while you use your glasses or contacts. You might also be asked to read letters or numbers from a card held 14 inches (36 centimeters) from your face. This will test your near vision.
- No special preparation is necessary for this test.
- There is no pain during the Visual Acuity Test.
The visual acuity test is a routine part of an eye evaluation or basic health examination, especially if there is a change in vision or an issue with vision.
In children, the test is performed to evaluate for vision issues. Vision issues in kids can typically be fixed or improved. Undiscovered or neglected issues may lead to permanent vision damage.
There are other ways to inspect vision in really young kids, or in people who do not know their letters or numbers.
What Is Normal Results for Visual Acuity Test?
Visual acuity is expressed as a fraction.
The leading number refers to the distance you stand from the chart. This is frequently 20 feet (6 meters).
The bottom number shows the range at which a person with normal vision could check out the same line you properly check out.
For instance, 20/20 is considered normal. 20/40 shows that the line you correctly check out at 20 feet (6 meters) away can be read by a person with normal vision from 40 feet (12 meters) away. Outside of the United States, the visual acuity is revealed as a decimal number. For instance, 20/20 is 1.0, 20/40 is 0.5, 20/80 is 0.25, 20/100 is 0.2, and so on.
Even if you miss out on one or two letters on the smallest line you can read, you are still considered to have vision equal to that line.
What Abnormal Results of Visual Acuity Test Mean
Abnormal results might be a sign that you need glasses or contacts. Or it might mean that you have an eye condition that needs further assessment by a supplier.