A rough estimate of convergence at reading distance is the String Test. The string test measures convergence or the eyes' ability to team together and focus in on a point at the normal reading distance. This test is not designed to replace an examination by an optometrist. We recommend that if the test is positive, to seek the services of an optometrist.

The string test is very simple and only requires about a minute of time. We feel it can provide much information. It only requires a four foot piece of string with a knot in the middle.

Step by Step Instructions: The String Test.

1. Obtain a four foot long piece of string and put a knot in the middle of the string so that the string looks something like this:

2. Tell the participant to make a fist with the dominate hand and measure from the middle knuckle of the middle finger to the elbow. The measurement is to be made with the string by placing the knot of the string at the person's middle knuckle of the middle finger when the hand is made into a fist. The string is to follow the curvature of the hand, down the arm to the elbow.

3. Have the person hold the string at the place where the string touched the elbow. This is the correct distance that a person should read from (the length from one's elbow to the middle knuckle when the person is making a fist). The person takes the string at that point and puts it onto their nose.

4. The participant looks down the string to the knot. The examiner holds the other end of the string. The knot will be between the participant and the examiner.

5. The participant is asked to notice what they see when they look at the knot. Do they see one string or two? Do they see one knot or two? If they see two strings, is one string brighter than the other or are they the same brightness?

6. The participant is then asked to draw what was seen.

7. The examiner interprets the participant's drawing and seeks clarification about the drawing. A correct drawing looks like this:

8. Anything other than this could indicate a problem with convergence (the test is positive) and the participant should be given a referral to a developmental optometrist.

Additional comments: This is a simple screen and should yield much information. Some people may need to do the string test once or twice before they understand what they are supposed to look at. The Brock String Exercise is a good remediation for those who fail (positive screen) the string test. We recommend that exercises be conducted under the direction of an optometrist.

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