Visual acuity test is one of the most common tests used to examine a person’s visual acuteness or clearness of vision or simply the eye sight. This test helps in measuring a person’s visual ability towards objects at near and far distances. The test is done with the help of a standardized eye chart. The visual acuity test can also be defined as a test that helps in detecting a person’s ability to recognize or read the smallest letters on a standardized eye chart held 14-20 feet away. In this test each of the two eyes are first tested separately and then together. If you are a person who already uses a corrective lens, then the test will be performed wearing that.
Alternative names of visual acuity test are Vision test- acuity and Eye test- acuity.
As mentioned earlier, the visual acuity test is done using a standardized eye chart. This is a simple test and can be done at hospitals, eye clinics, schools, health camps and at almost all places under the supervision of experts in the related field. The most commonly used eye chart is the Snellen eye chart. This eye chart consists of series of letters or letters and numbers which is larger in size at the top and gradually decreases towards the bottom. The patient will be asked to stay back about 20 feet away from the eye chart. The patient will then be asked to open both the eyes and then would be made to cover one eye with the help of a paper cup or with the help of palm. The patient will then be made to read all these letters or numbers from top to bottom loudly. The smallest line of letters or numerals that the patient can read detects the visual power of that eye. This is then repeated with the other eye. Patients who wear corrective glasses or contact lenses will be asked to read by wearing that. To test a patient’s near vision, the patient will be asked to read the letters and numerals written on the eye chart held about 14 inches away from the patient.
Different versions of this chart exists where each of these have specific characteristics. One such version is the Tumbling E chart which has the alphabet E written on it in four different directions. The patient standing at a specific distance from the chart must be able to recognize in which direction the alphabet E is facing.
The visual acuity of a person is expressed in fractions or Snellens fractions. Here, foot is used as the unit of measurement. As per this notation the normal vision is expressed as 20/20 vision where the numerator or the top number represents the testing distance in feet and the denominator number represents the visual acuity or the ability of patient’s eye to recognize the smallest line of letters on the chart. The patients visual acuity may be 20/30, 20/40, 20/60 etc. Greater the value of denominator, worse the vision will be. Surprisingly, if a patient’s visual acuity found is 20/10, then his visual ability is perfect than the normal. A patient with visual power of 20/200 is generally considered as blind.
The visual acuity can also be measured in meters and a visual acuity of 6/6 in meters is equivalent to the 20/20 vision in foot.
If the visual acuity test is done without wearing corrective glasses or contact lenses, then such a type of vision is referred to as Uncorrected Vision and if the test is performed wearing best glasses or lenses, then the vision is referred to as Best Corrected Vision.
An abnormal visual acuity result indicates that the patient needs further eye evaluation or the patient needs the use of corrective lenses and glasses to view normally.
The visual acuity test is usually done either as a part of general health check up or to detect any visual defect. Visual acuity test is used to detect the special resolving power of the visual processing system.
In children, the visual acuity test is used to screen any problem with vision so that it could be corrected or improved early. In many cases, the undetected or untreated visual problems may lead to permanent vision impairment.
For a patient suffering from vision impairment, his visual acuity test helps in determining the corrective lens power required to obtain the normal vision.
Even though no special preparations are required for this test, some of the points to be noted are: the patient should be cooperative and he should be able to understand the ototypes. The patient should also be able to communicate about the viewed ototypes to the physician. Thus, as the visual acuity test is a subjective test, a proper result cannot be obtained unless and until the patient cooperates with the physician. If the patient is under a condition that affects his mental consciousness like, if he is intoxicated, if he is in a sleepy mood or suffering with any health problems etc., then the visual acuity test may give a false result.