Abstract
Purpose: :
To investigate a possible relationship between pupil oscillations and eye movements.
Methods: :
We recorded both pupils and eye movements at 240 Hz. in 6 normal subjects using binocular infra-red video oculography. Each subject was instructed to fixate a 5mm. point in primary position for 40 seconds. This was repeated six times for each subject. For comparison we also recorded a fake eye eight times under different conditions to simulate the small movements of the subjects in primary position. Because of a prominent negative correlation secondary to blinks, trials having 9 or more blinks were eliminated leaving 23 trials for final analysis. Correlations between the pupil size and both horizontal and vertical movements were calculated. The changes in horizontal and vertical position as well as pupil size were broken down by frequency components based on a singular value decomposition and similar bands for eye movements and pupils were also compared using correlation coefficients.
Results: :
The average correlation coefficients of pupil to vertical and horizontal movements for the fake eye were 0.078, and -0.029 respectively. In comparison the correlation coefficients comparing pupil with vertical movements averaged 0.30 and 0.17 and pupil with horizontal movements was -0.0156 and -0.067 for right and left eyes respectively. The correlations between lowest frequency components from the transform matrix generated by a singular value decomposition for pupil and vertical eye movements had an average correlation of 0.34 and 0.19 for the right and left eyes respectively. The average for the fake eyes was 0.11. All values comparing the vertical movements and pupillary oscillations were significantly different for subjects compared to the fake eye while the relationships between subjects’ horizontal movements and those of the fake eye were not significant.
Conclusions: :
This study shows a surprising correlation between pupillary oscillations and vertical eye movements during fixation at primary position. This suggests that the centers controlling spontaneous pupillary oscillations and vertical eye movements during fixation share a common pathway.
Keywords: eye movements • pupil • ocular motor control