Visually Evoked Potential Markers of Concussion History in Patients with Convergence Insufficiency

Abstract

Purpose: 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.

FIGURE 1

Receiver operating characteristic curve for diagnosis of concussion history based on the mean P100 latency for (0.25-cycle/degree vertical sinusoidal grating >119 milliseconds or 0.50-cycle/degree vertical sinusoidal grating >113 milliseconds) and mean 0.50-cycle/degree vertical sinusoidal grating amplitude <14.75 μV. Area under the curve = 0.86 (P < .01); sensitivity, 0.92; specificity, 0.80.

FIGURE 2

Receiver operating characteristic curve for diagnosis of concussion history based on at least 2-millisecond latency lag for 0.50- and 0.25-cycle/degree vertical sine wave stimuli compared with checkerboard stimuli. Area under the curve = 0.76 (P < .01); sensitivity, 0.74; specificity, 0.79.

FIGURE 3

The sum of mean amplitudes for visually evoked potential responses to 0.50-cycle/degree vertical sinusoidal grating as a function of response latency for convergence insufficiency patients with and without concussion history.