Blog: The Clinical Utility of Objective Convergence Measures in Concussion Assessment
This month, we’ll be introducing our newest concussion product feature, the objective convergence assessment. This paradigm features automated measures of both eyes as they follow a target as it moves from distance to the Near Point of Convergence (NPC) and back to the position of origin. Convergence measures have been demonstrated to be one of the single most sensitive measures of concussion visual subtypes, and have become a central aspect of vestibular and ocularmotor assessment. In recent years, assessing for abnormal convergence has become more common among neurological and TBI specialists, particularly for those treating adolescents with concussion.
Convergence Insufficiency (CI) is a binocular vision disorder that impacts the ability of the eyes to converge together at the same location on a near visual target. After concussion injury, this can manifest in symptoms such as headache, double vision, eye strain and difficulty with every day activities such as reading and writing. Many neurological clinical specialists are relying on the measurement of NPC to identify the severity of this dysfunction, although Convergence Insufficiency may not be solely linked to receding NPC measures. As a result, additional studies are underway to further investigate the increase in eye jitter that occurs during vergence movements in patients with confirmed CI. Some specialists believe these subtle eye movements may also hold relevant clinical utility to the identification of CI, in addition to current practices involving NPC measures.
The EYE-SYNC convergence assessment consists of three critical measures, and can be completed as a single trial or as an average of three continuous trials. Objective data is gathered during the assessment, with the following variables included in the report:
Near Point of Convergence (NPC)
Near Point of Convergence is a measurement of the point at which visual axes are maximally converged while producing a single binocular image of an object in focus. Beyond this point, exophoria of one eye (typically) is observed, and double vision is produced. The measurement of NPC is measured in centimeters from the nose to this “break” point.
Figure 1. The EYE-SYNC Convergence Assessment.
Near Point of Convergence Recovery
The NPC recovery distance is a measurement of the point at which double vision resolves and a single binocular image is restored. This is also measured in cm from the nose and is often referred to as the “break” recovery point.
Figure 2. Capturing of exophoria at the NPC.
Variance measures refer to the amount of gaze error present, in comparison between each eye and eye to target. The variance measure is a standard deviation of error and includes the precision and accuracy of gaze positions that occur during the assessment and at the moment of exophoria. These measures can be utilized to determine the amount of fixation disruption present during the assessment duration, as well as to identify the severity of exophoria that occurs at the NPC (Figure 2).
Figure 3. Eye jitter captured during a convergence assessment after concussion.
It is our hope that with the addition of Convergence measures, clinicians will develop a more comprehensive picture of the type and severity of ocularmotor dysfunction. In doing so, even more specific and targeted therapies can be applied sooner, enabling the objective monitoring of recovery. For patients, initiating the correct therapy for convergence insufficiency can improve outcomes and limit lost time away from school, sports and work.