All the information you should know before going for an Eye Test

An eye test is a basic test undertaken in order to test the vision using a eye charts. In this they measures how you can see from a distance

Visual acuity eye test

Visual acuity test is the basic eye test performed by the ophthalmologist, an optometrist or an optician. It can also be done by a nurse or a technician. In visual acuity test, the ability of a person to see and distinguish between different shapes and details is tested. This eye test also includes other factors including colour vision, peripheral vision and depth perception of the eye. It is a physical eye test and does not require any machines which come in contact with the eyes. It is the most frequently used eye test to determine any vision problem or helps us to know if our vision has changed. There are some organizations which take visual acuity test in order to recruit people for certain jobs. This test helps in the early detection of vision-related problems and can prevent from the situation getting worse.

What does 20/20 means in an eye test result?

Visual acuity test is done by either using a Snellen chart or a random E chart. Visual acuity is measured in the fraction. Having a fraction number of 20/20 is considered as a normal vision which means that if you are standing 20 feet away from an object then you can see it clearly. If you have a fraction number of 20/40 then, it means that for an object placed at a distance of 40feet you need to be at 20 feet away from the object in order to clearly see it as a person with normal vision would be able to see the object when standing 40feet away from the object. This type of fraction indicates that there is a need for you to wear corrective eye lenses to correct your vision. 20/20 is considered as a normal vision fraction number any deviation in this number indicates a vision problem in an individual. The result of the eye test is then used to diagnose conditions like myopia, hyperopia, astigmatism or presbyopia and appropriate corrective lenses are suggested to obtain a 20/20 vision using them.

Procedure of the visual acuity test

The procedure of the eye test is very simple and does not require any physical contact of the machine on the eye. In this test,the person is required to remove any eye glasses or eye lenses and then stand or sit 20 feet or 6meters away from the screen which is used to show the letters and characters. Then you would be asked to put your palm to cover your one of your eye. With the other eye, you would be asked to read the letters present on the screen in front of you. Lines and pictures are used for small children and people who cannot read. This process is then repeated with the other eye and the line till which you can read clearly is noted.

In the second round of tests, a screen would be present 14 inches away from you and you would require to repeat the above-mentioned steps. In this test, your vision for objects placed in the near vicinity is checked. After this, the technician would put on the corrective lenses and check again so that a vision of 20/20 could be obtained.

Charts used in an eye test

The charts used in the eye test are the Snellen chart and the random E chart. When you visit a doctor or optician for your eye check-up then they would ask you to remove the eyeglasses and lenses your wearing. They would then ask you to read from the chart present in front of you. This chart is known as the Snellen chart.

Snellen chart was invented by a Dutch eye doctor named Hermann Snellen in the 1860s. The Snellen chart consists of 11 rows with different alphabets present in capital letters. The first row has the largest sized single capital letter and then as we proceed to the other rows the letters keep reducing in size and the last row has the smallest sized letter placed in them. If your vision test results come out with a fraction number of 20/20 then it is considered as a normal vision. If the fraction number deviates from the normal value then the corrective lenses are used to enhance the vision and make it normal vision by the help of eye lenses.

Dr. Snellen also created the random E or the tumbling E chart. This chart was specially designed for the eye test of people who didn’t know how to read. In this type of chart capital letter, E is used. The person taking the eye test is asked to point out the direction in which the arms of E are projected. The same calculation of fraction number is done as in the Snellen chart.

The jaeger eye chart is used to test the near vision of the person. In this eye test, a small hand-held chart is put up in front of the person approximately 14inches away from them. The chart contained paragraphs written in different font sizes ranging from J10 to J1. J10 is considered to have the largest font size and J1 is considered to have the smallest font size. The size may vary from person to person using different cards as the standardized sized chart is not available till now. The result of the eye test is similar to the distant vision test. In this the chart can be moved in front of the person or away from them till particular font size becomes visible to them.

Limitations of the eye charts

The eye charts used in the visual acuity test are considered as reliable method for testing as they do not require physical contact of any machine in the eye. The eye test can be done physically and the vision can be evaluated easily. But they only provide results based on the distance related problems of the vision. The eye charts can’t be used for measuring colour perception, peripheral vision and depth perception. They are also not helpful in determining the health of the eyes. It is unable to detect various eyes related problems and injury. It can’t determine the condition and shape of the retina. Eye charts are considered as one part of the complete eye test due to their limitations mentioned above.

In order to have a complete eye test one should get the following tests done. The first is the visual acuity test which was discussed earlier. Then comes the colour blindness test which detects the colour vision deficiencies in a person. Ocular motility test is done in order to determine the movement of the eyes when objects is passed quickly. Stereopsis test is done to determine the depth perception of the eyes. Retinoscopy is done to correctly measure the power of lenses that would be required to correct the vision. Glaucoma test is performed to measure the pressure inside the eyes. These all test are included in the comprehensive eye test exam. The contact lens prescription is done when there is no dilation of the pupil. It is not included in the complete eye test but is done separately by the same or different doctor or eye specialist. The test results can be used for making the eye glasses but are not used for making the contact lenses.