Baseline blink rates and the effect of visual task difficulty and position of gaze

Purpose. To compare the baseline blink rates (BBR) measured under different (baseline) conditions, and to compare the blink rates measured when performing two visual tasks of different levels of difficulty at two positions of gaze. Methods. In the first single masked experiment, BBR were measured under three different conditions - (i) conversation with the subjects (ii) taking the visual acuity and (iii) keeping the subjects waiting in an empty examination room. In the second single masked experiment, the subjects were required to perform an easy task treading normal English words) and a difficult task treading mirror-image English words) at primary gaze and down gaze. The orders of the tasks performed were randomly allocated. Results. BBR taken under the three different conditions were significantly different from each other. No significant difference was found between the blink rates measured when performing the two reading tasks if they were performed at the same position of gaze. The mean blink rates were significantly lower when performing the tasks at down gaze than when performing the tasks at primary gaze. No significant differences were found between BBR-waiting and blink rate measured when the subject was doing the easy task at primary gaze, and between BBR-VA and blink rate measured when the subject was performing the difficult task at primary gaze. Conclusions. BBR measured under different (baseline) conditions produced different results so it is important for investigators to describe the baseline condition very clearly in studies where BBR are measured. Our results also indicated that mean blink rate was affected by the position of gaze and not the level of task difficulty.