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visual acuity

Visual acuity is the ability of the eye structure to clearly identify the images and Appreciate its details in a properly lit environment.

Given this definition, many may think that those who enjoy excellent visual acuity do not present any refractive defect, and this is not so.

It should not be confused with prescription, as a person can enjoy good visual acuity by wearing glasses or contact lenses.

En Área Oftalmológica Avanzada We explain below what visual acuity is and how it can be measured.  

What is visual acuity?

Visual acuity is the ability of the visual system to identify stimuli that become images and to be able to appreciate details and characteristics of them. 

In the case of people with myopia, farsightedness o astigmatism, visual acuity will be the maximum vision they can get with the adjusted graduation. 

For a person to enjoy good visual acuity, many factors are involved such as the proper functioning of the eye, the state of the optic pathway, the retina, the visual cortex, if the patient suffers myopia, farsightedness o astigmatism, the illumination of the environment and the distance to which the objects are ... 

There are also factors that can make a person significantly compromised his visual acuity:

As measured?

Visual acuity can be measured in both eyes, even if they have or do not have refractive defects from near, far, separately or in both eyes at the same time.

All this is carried out through the optotypes, which are no more than the instruments that the ophthalmologist or optometrist used to test visual acuity. 

The measurement can be done through letters, numbers, words, symbols, figures or drawings.

The most used is the arithmetic scale or Snellen type.

To perform the measurement, the patient must be without glasses or contact lenses, sit 20 meters away from the Snellen table and start reading the lines of letters, numbers or words that the specialist indicates.

The test is first done on one eye while the other is covered with the hand, a splint, or opaque glass.

The visual acuity test is the Ophthalmological examination best known, lasts a few minutes and does not require any prior preparation.

Visual acuity values

The results of the test are obtained immediately and have values ​​in decimal scale or in fraction form.

The values ​​of a person with 100% visual acuity would be 1.0 in decimal scale and 20 / 20 in fraction.

In the scale of visual acuity expressed in fraction, the upper number represents the distance the patient is at the time of the test (20) while the lower number indicates the distance in which a person with normal vision can read the letter that would correspond to a vision of the 100%.

Therefore, under the Snellen fractions, if we have a visual acuity half as good as we consider normal, we will have a visual acuity of 20 / 40 or, in decimal system 20 / 40 = 0,5

A person can also present values ​​of more than one 20 / 20 or 1.0 in the vision. It is the case of those patients who see better than the average, in these cases, if we have a vision of 20 / 10 or on the decimal scale 2.0 we will see twice as much as a normal person.

In case of having a visual acuity better than normal, the usual values ​​are 20 / 15 or an 120% acuity vision.

Abnormal results may indicate that a person needs to use glasses or contact lenses in order to correct their visual acuity.

They can also be a sign of some type of more important condition that suggests more in-depth analysis.

If you have any questions or need to perform a Snellen test, contact us. In Área Oftalmológica Avanzada we will be happy to assist you. 

Summary
Visual acuity
Article name
Visual acuity
Description
Visual acuity allows us to clearly identify the images. We tell you what is in detail and how it is measured.
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Name of the editor
Área Oftalmológica Avanzada
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Synonyms:
visual acuity
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