Evaluation of quantitative head impulse testing using search coils versus video-oculography in older individuals

Abstract

Objective: To evaluate the validity of 2D video-oculography (VOG) compared with scleral search coils for horizontal AVOR gain estimation in older individuals.

Study design: Cross-sectional validation study.

Setting: Tertiary care academic medical center.

Patients: Six individuals age 70 and older.

Interventions: Simultaneous eye movement recording with scleral search coil (over right eye) and EyeSeeCam VOG camera (over left eye) during horizontal head impulses.

Main outcome measures: Best estimate search coil and VOG horizontal AVOR gain, presence of compensatory saccades using both eye movement recording techniques.

Results: We observed a significant correlation between search coil and VOG best estimate horizontal AVOR gain (r = 0.86, p = 0.0002). We evaluated individual head impulses and found that the shapes of the head movement and eye movement traces from the coil and VOG systems were similar. Specific features of eye movements seen in older individuals, including overt and covert corrective saccades and anticompensatory eye movements, were captured by both the search coil and VOG systems.

Conclusion: These data suggest that VOG is a reasonable proxy for search coil eye movement recording in older subjects to estimate VOR gain and the approximate timing of corrective eye movements. VOG offers advantages over the conventional search coil method; it is portable and easy to use, allowing for quantitative VOR estimation in diverse settings such as a routine office-based practice, at the bedside, and potentially in larger scale population analyses.

FIG. 1

Correlation between search coil and VOG HIT gains. Search coil gains are calculated based on the best estimate of gain in the 30-ms window preceding peak head velocity, whereas VOG gains are calculated based on the best gain between 30 and 60 ms after onset of head movement. Search coil and VOG gains are significantly correlated (r = 0.86; p = 0.0002), and the slope of the regression line is y = 0.84x + 0.22, where x corresponds to search coil gain and y corresponds to VOG gain.

FIG. 2

Head and eye movement traces during head impulse testing on a single individual using search coils (A) versus video-oculography (B). In all panels, head movements are in red, and eye movements are in blue. The x-axis corresponds to time in milliseconds (ms); the axes for search coil and VOG are somewhat offset, given differences in the systems regarding when the first head impulse occurs relative to time 0, that is, the offset does not represent real-time latency differences. Note the covert saccades (occurring during head movement) and overt saccades (occurring after head movement stops) present in both the search coil and VOG data for both right- and leftward head impulses.

FIG. 3

Individual head velocity traces in red (A and B) and eye velocity traces in blue (C and D) for the first 6 consecutive head impulses using the search coil (A and C) and VOG (B and D). The x-axis corresponds to time in seconds; the axes for search coil and VOG are somewhat offset, given differences in the systems regarding when the first head impulse occurs relative to time 0, that is, the offset does not represent real-time latency differences. The EyeSeeCam records head movements in 3D (yaw, pitch, roll) and eye movements in 2D (yaw and pitch); these same axes were used for search coil recording also.

FIG. 4

Head and eye movement traces during head impulse testing on a single individual using search coils (A) versus video-oculography (B). In all panels, head movements are in red, and eye movements are in blue. The x-axis corresponds to time in milliseconds (ms); the axes for search coil and VOG are somewhat offset given differences in the systems regarding when the first head impulse occurs relative to time 0, that is, the offset does not represent real-time latency differences. Note the anticompensatory saccade present in both the search coil and VOG data for both right- and left-ward head impulses.