Brock String Vision Therapy

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There are hundreds of different vision therapy activities, each specifically designed to help a certain ocular condition, one of the most common vision therapy is the Brock string.

Brock String with 5 beads

A Brock string is an instrument used in vision therapy in the eye of a patient having inadequate convergence and other anomalies of binocular vision. It is a simple procedure employing the principle of physiological diplopia which is a fundamental property of normal binocular vision. Whereas all object points lying on the horopter curve (falling within panum’s area) stimulate the corresponding points and are therefore perceived as single.

In order for a patient to perceive physiological diplopia, he or she must exhibit normal sensory fusion without suppression. Therefore, physiological diplopia is an important tool in the orthopic treatment of strabismus.

It consists of a white string approximately 10 feet in length with three (five) small plastic beads of different colors that can be moved to various positions along the length of the string.


Girls doing Brock String vision therapy

Uses of Brock String

In general, Brock string therapy is used for purposes:
1. To assist in the voluntary convergence (Convergence Insufficiency)
2. To train and monitor the binocular fixation (Strabismus)
3. To improve the quality of sensory fusion (suppression)
4. To train the flexibility of vergence( fusional exercise)


  • The patient should be seated or standing in a relaxed, balanced posture.
  • Attach one end of the string to a stationary object at a height slightly below eye level
  • The patient holds the other end of the string just below the nose, exactly on the mid-line procedure.

Recognition of physiological diplopia

  • A bead is positioned on the other end of the string, he or she converge the eye to look at bead with both eye open, the bead should be seen as one and the string should seen as two
  • The string should form an “inverted V” through the bead.
  • If the patient only sees one bead and one string when both eyes are open, he is suppressing one eye. To break the suppression
  • Again slid a bead on the center of the string from both ends and looked at the bead should appear single and the string should form anX” through the bead.
  • Again slid the bead near the nose(6cm from the nose) and looked at the bead should appear single and the string should form a broadV

Brock string

Jumps and introduction of fixation accuracy

  • When he or she is able to perform the single bead procedure (1) without difficulty, then all of the beads are placed on a string at equal distances,
  • He or she shifts his focus from one bead to another in random order, when looking at the far bead, The bead should appear single and the string should form an “inverted V” through the bead and other beads will appear slightly blurred and doubled.
  • Then shift his focus to the next bead which should appear single and the string should form an “X” through the fixing bead, and other beads will appear slightly blurred and doubled.
  • He or she shifts his gaze one by another to a closer bead (close to the nose) should appear single and a broad “V” will be made by the string, and other beads will appear slightly blurry and doubled.
  • Once the correct response is perceived (accurate fixation and no suppression), he or she shifts his or her gaze back and forth between the bead and, obtaining the physiological diplopia response as quickly and as accurately as possible, and near bead moved closer, repeated the procedure

brock string how to use


Bug on string

Push all beads to one end of the string. He or she looks at the far end of the string and obtains a “v” response and visualizes a bug walking slowly up the string toward him, as the slowly follow v should change into “x” and the x should move slowly and smoothly up the string toward him until reaches his nose.


Variation gaze

Repeat the above procedure 2(two) with the head turned to different positions: up, down, right, and left. The string keeps straight.


Accommodation and vergence system

Because the bead is not a critical accommodative target, accommodation can lag or lead to aid fusional vergence without resulting in blur response. At a later point of training (after gross vergence ability improved) a small letter can be taped to the bead. He or she keep the latter clear, in addition to maintaining accurate fixation. This modification is designed to improve the accuracy of both the accommodation and vergence systems.



Brock string exercise is one of the best and most recommended home vision therapy procedures. The duration of therapy differs in each case. While there are many uses for the Brock string, you will have the best success under the supervision of an eye care professional such as an optometrist or vision therapist.


Where to find Brock String in Nepal?

If you’re wondering where to find Brock String in Nepal, we’ve got you covered! Here are a few places where you can get your hands on this valuable tool

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