There is now a special tool that can directly measure visual acuity or your eyesight. This tool, called the autorefractometer, is already widely available in various eye clinics and optical stores. However, the traditional visual acuity examination should not be forgotten. How, though, is the traditional visual acuity examination procedure?
Eye examination with a Snellen (Snellen chart) card
Examination of eye acuity is generally carried out with the help of a Snellen or Snellen chart. This card was developed by an ophthalmologist from the Netherlands, Herman Snellen, in the 1860s. There are many variations of this Snellen card. However, in general there are eleven capital letter lines containing several types of letters. The lower the writing size will be smaller.
The meaning of the numbers on the Snellen card
You may have wondered what the numbers on each row of Snellen cards mean. This number has a special meaning. So, each line is equipped with a number which is the distance (usually in feet) where the eyes of normal and healthy people can read the letters on that line.
For example if there is a number 20/200 next to the first row of letters. The first number, which is 20, represents the distance between you and the Snellen card. Usually your distance with a Snellen card is indeed 20 feet or 6 meters away.
While the second number, which is 200, represents the distance at which your eyes are still able to read the letters in that line clearly. The number 200 means 200 feet or 60 meters.
Eye vision assessment
The sharpness of visual vision of a normal human eye is 20/20 or in meters 6/6. This means that within a distance of 20 feet or 6 meters, your eyes are still sharp enough to see the writing that can normally be read from that distance.
However, if your vision is 20/40, it means that your eyes with a distance of 20 feet or 6 meters can only read large enough letters that can be read at a distance of 40 feet or 12 meters.
Eye examination procedure with Snellen card
Now you understand the basis of visual acuity. Well, here is a discussion about eye examination procedures with Snellen cards.
- Make sure the room has enough light.
- You will be asked to sit or stand at a distance of 6 meters from the Snellen card.
- Cover one of your eyes with your hand. If available, you might be wearing special glasses with an eye patch.
- Check your left and right eyes separately. Eyes with a more opaque view will be tested first.
- Start reading from the top row to the bottom, so you are no longer able to read the letters on that line. Read in a loud and clear voice.
- If the results of the examination do not reach the letter line 20/20 or 6/6, the procedure will be repeated using pinhole glasses. If the pinhole visus is repaired, then vision problems can be caused by refractive abnormalities such as nearsightedness (myopia).
- Repeat this procedure for the next eye.
Another way to check eye vision
Usually using a Snellen card is enough to assess a person's visual acuity or vision. However, in certain cases where you are completely unable to read letters that are too opaque, the examiner or ophthalmologist will use your hands.
First, you will be asked to count the number of examiner's fingers from one to six meters. If you cannot calculate it, the examiner will move his hand. If you still can't see clearly, the examiner will use lights or lighting.
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