R R

What Is the Brock String Test?

The Brock string is a primary tool used in vision therapy to develop and refine binocular coordination. Developed by Dr. Frederick Brock, it consists of a white string, typically ten to fifteen feet long, with three or more differently colored beads that can be moved to various positions along the length of the cord. One end of the string is held at the tip of the patient's nose while the other is attached to a fixed point, such as a doorknob. This simple device provides immediate visual feedback to the patient, allowing them to "see" how their eyes are working together in real time.

Link to This Resource Page

Provide a valuable resource to your clients or customers by linking to this resource page. Just place the following link on your website.

To display this...

What Is the Brock String Test?

The Brock string is a primary tool used in vision therapy to develop and refine binocular coordination. Developed by Dr. Frederick Brock, it consists of a white string, typically ten to fifteen feet long, with three or more differently colored beads that can be moved to various positions along the length of the cord. One end of the string is held at the tip of the patient's nose while the other is attached to a fixed point, such as a doorknob. This simple device provides immediate visual feedback to the patient, allowing them to "see" how their eyes are working together in real time.

read more about brock string test ...

Copy this HTML:

Copy HTML Copied!

Mechanism: Physiological Diplopia

The Brock string utilizes the concept of physiological diplopia, which is the normal doubling of objects that are not at the specific distance where the eyes are currently focused. When a patient looks at a specific bead, the brain should ideally perceive a single bead with two strings entering it and two strings exiting it, forming an "X" pattern. This "X" indicates that both eyes are pointing accurately at the same target. If the strings cross in front of or behind the bead, it reveals that the eyes are over-converging or under-converging.

Treating Convergence Insufficiency

The most common use for the Brock string is in the treatment of convergence insufficiency (CI). This is a condition where the eyes struggle to stay turned inward during near tasks like reading or using a computer. Patients with CI often experience "suppression," where the brain ignores the input from one eye to avoid double vision. The Brock string makes this suppression visible; if the patient sees only one string instead of two, they know their brain is "turning off" one eye. This immediate feedback allows the patient to consciously work on re-engaging the suppressed eye.

Advanced Coordination Drills

As a patient progresses in vision therapy, the Brock string is used for more complex "jump" transitions. The clinician will instruct the patient to shift their focus rapidly from a near bead to a middle bead and then to a far bead. The goal is to achieve an instant, stable "X" pattern at each location without the string "shimmering" or one string disappearing. These exercises build the stamina and flexibility of the extraocular muscles and the neural pathways responsible for binocular fusion, which translates to more comfortable and sustained focus during daily activities.

Identifying Common Errors and Suppression

During the test, several visual "errors" can occur that help a therapist diagnose specific binocular issues. If a patient sees only one string, it indicates total suppression of one eye, whereas seeing the strings "flicker" suggests intermittent suppression. If the strings appear to cross at a point closer to the nose than the actual bead, the patient is over-converging, a condition known as an esophoric posture. Conversely, if the strings cross behind the bead, the patient is under-converging, known as exophoria. Correcting these errors through repeated practice helps the brain recalibrate its internal map of where objects are located in physical space.

FAQs on the Brock String

Why do I see the "X" behind the bead instead of at it?

This usually indicates that your eyes are "over-aiming" or converging in front of the actual target. In vision therapy, this is often called being "esophoric" at near. The Brock string helps you learn the internal feeling of relaxing your eye muscles to move the "X" back to the bead.

Can I do this at home?

Yes, the Brock string is frequently assigned as "home reinforcement" vision therapy. However, it should be performed under the guidance of a developmental optometrist to ensure you are not practicing "bad habits" or reinforcing suppression patterns without realizing it.

Does it help with sports?

Many athletes use Brock string variations to improve their depth perception and reaction times. By training the eyes to converge and diverge rapidly and accurately, athletes can better judge the speed and distance of moving objects like baseballs or tennis balls.

When to Discuss the Brock String with Your Doctor

If you or your child experience frequent headaches during reading, blurred vision that comes and goes, or a sensation that words are "floating" on the page, you should seek a binocular vision evaluation. The Brock string is often the first step in a customized therapy plan designed to eliminate these symptoms by training the eyes to work as a synchronized team.

References

https://www.covd.org/page/vision_therapy
https://pubmed.ncbi.nlm.nih.gov/15110668/
https://www.sciencedirect.com/topics/medicine-and-dentistry/binocular-vision-disorder