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Brock String

Draftsensory70%beginnermoderate evidence
View FHIR resourceFHIR R4 ActivityDefinition — the interoperable form of this exercise

Positions & Range of Motion

Start
Seated upright, string held from the bridge of the nose to a fixed anchor point, gaze fixating the nearest bead
End
Gaze converged sequentially onto each bead along the string so the fixated bead appears single with two strings crossing through it (physiological diplopia of the others)
Range of Motion
No joint motion — ocular vergence and accommodation excursion only; head held still

How to Perform

A string with 3–5 colored beads is held from the bridge of the nose to a fixed point. The user fixates each bead in sequence; correct fixation produces a single bead with two strings crossing through it (physiological diplopia of the un-fixated beads).

Watch on YouTube

Opens a YouTube search for “Brock String

Equipment:brock string
Starting position: seated

Coaching Cues

  1. 1

    When fixating the bead, the other beads should appear doubled — that's the X pattern of physiological diplopia

    (verbal)
  2. 2

    If one string disappears, that eye is suppressing — close the other and reopen to re-engage

    (verbal)

Evidence-Based Dosing & EMG Data

Recommended Dosing

5–10 minutes/day as part of an office-based vergence program (CITT pattern).

Muscles Involved (0)

No muscles linked.

Easier Variations ↓

1

Two-Bead String

Reduce to two beads at fixed distances to simplify the vergence task.

Harder Variations ↑

1

Jump Vergence with String

Alternate fixation between far and near beads without smooth scan.

Research Notes

Develops fusional vergence awareness and helps suppress suppression. Evidence sits within the broader CITT vergence/accommodative therapy program rather than as an isolated intervention [Scheiman 2020 Cochrane; Chang 2021 Ophthalmology].