Brock String / Convergence Training

A Brock string is the simplest way to begin training your vision. It consists of a string with colored balls. The athlete has the string in front of him or her at nose level and parallel to the ground. The athlete then practices focusing on each ball, one at a time, from front to back and back to front. This helps improve the speed at which the eye adjusts. Both the eye muscles and muscles inside the eye can be trained.

How to Use the Brock String

Set Up:

  1. Make a loop at the end of both of the white string.
  2. Affix one end of the string to a doorknob.
  3. Position the far bead near the end of the string closer to the doorknob. This is the far fixation bead.
  4. Place the middle fixation bead about 2 ft -5 ft from you.
  5. Place the near fixation bead about 6 inches from your nose.
  6. Stand or sit directly in front of the doorknob facing it. Put the loop around your index finger and hold the white string under your nose like a mustache, 
  7. Hold the cord up to the bridge of your nose so that the cord is stretched tight between your nose and the doorknob.

Brock String Vision Therapy Procedure:

  1. Look at the near fixation bead. Keep this bead single as you look directly at it. If the near bead is double this indicates an eye teaming problem. if this occurs, move the near bead closer or further away until you see it as a single bead. The near bead should be moved closer and closer as the task becomes easier. 
  2. Eventually, the near bead should be only one inch from the bridge of your nose.
  3. As you look at the near fixation bead you should see two strings, each of which appears to come from your eyes. if your fixation of the bead is accurate, the two strings should appear to meet exactly at the bead forming an “X”. As the bead is moved into one inch from your nose, the two strings should appear to meet exactly at the bead forming a “V”.
  4. Shift your eyes to the middle fixation bead and then to the far fixation bead and repeat. if your fixation of the far bead is accurate, the two strings should appear to meet exactly at the bead forming a “V”.
  5. Change the location of the fixation beads and again repeat.

Try to be aware of other objects periphery or in your field of view as you practice.

Below is a series of examples. The string on the right side shows the actual “top-down” location of the green, yellow, and red beads. The image to the left shows what you would see if both eyes are focusing on a single bead. Notice that double vision, in this case, is normal – this is called physiological diplopia.

Brock String 1

In this first example, look at the nearest (green) bead. The green bead should appear single and a broad “V” will be made by the string. Both the yellow and red beads will appear slightly blurry and doubled.

Brock String 2

In the second example, look at the middle (yellow) bead. The yellow bead should appear single and the string should form an “X” through the yellow bead. Both the green and red beads will appear slightly blurred and doubled.

Brock String 3

In the third example, look at the far (red) bead. The red bead should appear single and the string should form an “inverted V” through the red bead. Both the green and yellow beads will appear slightly blurred and doubled.

Brock String 4

Let’s look at one final example. Here the left eye is turned outward in a condition called exotopia. This is an example of strabismus – many athletes with strabismus also suppress images from the turned eye so that the person doesn’t see double constantly. In this example, the an athlete suppresses the left eye’s images and would not see the “X” that a trained athlete would see.

What does the Brock String do?

The purpose of this training exercise is to optimize an athletes abiity to see with both eyes simultaneously. When you look at the first bead should see one bead with two short strings leading toward it and two longer strings leaving it. Additionally you should see two strings entering the bead and two strings leaving it, making a large“X”. The beads that are not being looked at will appear in the distance on each of the white strings you see coming out or in from that fixation bead.

Why is the Brock String important in sports vision?

The Brock string is a great detection tool to help identify if you may have problems with convergence (such as convergence insuficency or Convergence Excess) or suppression. The Brock string is also used therapeutically in vision therapy to help any athlete develop skills of convergence as well as to disrupt suppression.

After you complete this basic level of trying, we can advance your training by altering your gaze, the range or by employing lenses and prisms, but we’ll get to that a bit down the road.

But wait, there’s one more important point. As with all training; “Form Matters”, so maintaining proper posture, whether sitting or standing will help you get the most from your time on the string.