Visual pursuit of one’s own face in disorders of consciousness: a quantitative analysis

Background: Eye behaviour is important to distinguish minimally conscious state (MCS) from vegetative state (VS). Objective: To search for conditions most suitable to characterize patients in MCS and in VS on quantitative assessment of visual tracking. Design: This is a cross-sectional study. Participants: In total, 20 patients in VS, 13 in MCS plus and 11 in MCS minus participated in this study. Setting: Neurorehabilitation Unit. Methods: Evaluation of eye behaviour was performed by infrared system; stimuli were represented by a red circle, a picture of a patient’s own face and a picture of an unfamiliar face, slowly moving on a personal computer (PC) monitor. Visual tracking on the horizontal and vertical axes was compared. Main outcome measures: The main outcome measures were proportion of on-target fixations and mean fixation duration. Results: The proportion of on-target fixations differed as a function of the stimulus in patients in MCS plus but not in other groups. Own face and unfamiliar face elicited a similar proportion of on-target fixations. Tracking along the horizontal axis was more accurate than that along the vertical axis in patients in both MCS plus and MCS minus. Fixation duration did not differ among the three groups. Conclusions: Horizontal visual tracking of salient stimuli seems particularly suitable for eliciting on-target fixations. Quantitative assessment of visual tracking can complement clinical evaluation for reducing diagnostic uncertainty between patients in MCS or VS