Visually Evoked Potential Markers of Concussion History in Patients with Convergence Insufficiency
We investigated whether differences in the pattern visual evoked potentials exist between patients with convergence insufficiency and those with convergence insufficiency and a history of concussion using stimuli designed to differentiate between magnocellular (transient) and parvocellular (sustained) neural pathways.Methods
Sustained stimuli included 2-rev/s, 85% contrast checkerboard patterns of 1- and 2-degree check sizes, whereas transient stimuli comprised 4-rev/s, 10% contrast vertical sinusoidal gratings with column width of 0.25 and 0.50 cycles/degree. We tested two models: an a priori clinical model based on an assumption of at least a minimal (beyond instrumentation’s margin of error) 2-millisecond lag of transient response latencies behind sustained response latencies in concussed patients and a statistical model derived from the sample data.Results
Both models discriminated between concussed and nonconcussed groups significantly above chance (with 76% and 86% accuracy, respectively). In the statistical model, patients with mean vertical sinusoidal grating response latencies greater than 119 milliseconds to 0.25-cycle/degree stimuli (or mean vertical sinusoidal latencies >113 milliseconds to 0.50-cycle/degree stimuli) and mean vertical sinusoidal grating amplitudes of less than 14.75 mV to 0.50-cycle/degree stimuli were classified as having had a history of concussion. The resultant receiver operating characteristic curve for this model had excellent discrimination between the concussed and nonconcussed (area under the curve = 0.857; P < .01) groups with sensitivity of 0.92 and specificity of 0.80.Conclusions
The results suggest a promising electrophysiological approach to identifying individuals with convergence insufficiency and a history of concussion.