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Brock String Exercise

A Brock string is a common tool used in vision therapy. It’s made up of a flexible white rope or string that’s about 10 to 15 feet long, that is lined up with colored wooden beads that move along the length of the string. Patients with convergence insufficiency, amblyopia (lazy eye) and strabismus (eye turn) commonly use the Brock string to strengthen specific visual skills.

There are two types of problems with the vergence system: those at close range and at a distance. To maintain clear, single vision, convergence and divergence skills must be quick, accurate, and consistent. Symptoms of a vergence dysfunction include double vision, blurred vision, headaches, and visual discomfort. Furthermore, vergence dysfunction impairs the visual-vestibular pathway, resulting in dizziness and balance issues.

What Is the Purpose of the Brock String Exercise?

The goal of the Brock string exercise is to help patients with vergence problems develop convergence skills and disrupt suppression.

Moreover, this exercise can be used as a diagnostic tool, providing instant feedback on whether their eyes are working as a team to focus on an object at various distances.

The Brock string is made up of two strings (each of which has beads affixed to them) that enter a central bead and two strings that leave it, creating a large“X”. As part of the exercise, patients are requested to alternate fixation and focus from one bead to the next while maintaining awareness of physiological diplopia. For example, patients may be instructed to fixate on a near bead, and if they see double, this indicates a problem with eye teaming. At this point, the patient will be instructed to move the bead closer or further away until he or she sees only one bead. To strengthen the visual skill, the patient will repeat this exercise several times over.

The activity can be altered to make it easier or more difficult by bringing the beads closer/further to the nose and/or by employing lenses and prisms.

Why is the Brock String Important in Vision Therapy?

The Brock string exercise can be used to diagnose and treat visual problems, including lazy eye, convergence insufficiency and other deficiencies in a person’s visual skills. This is critical since these issues can cause eye strain, headaches, blurry vision, balance issues and other problems. A concussion or other type of brain injury can also induce these same symptoms.

The Brock string exercise is divided into two parts: convergence and suppression.

Convergence occurs when both eyes are not focused correctly; they focus behind an object rather than directly on it. So in this context, a person with convergence insufficiency may struggle to maintain their focus on a single bead. If this is one of your issues, you may be experiencing eye strain or double vision.

Suppression occurs when the brain disregards the signals that one of the eyes sends to the brain. When looking at a Brock string you may only see one string instead of two, or one string may appear and then disappear. You will only see one field of vision, which may affect your balance and peripheral vision.

While the Brock string has numerous applications, it is not a do-it-yourself project; you will have the best results under the supervision of a vision therapy optometrist. Contact Grand Developmental Vision Institute to learn more about the Brock string exercise and vision therapy.

Our practice serves patients from Winnipeg, Selkirk, Portage La Prairie, and Brandon, Manitoba and surrounding communities.
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