A technique for determining convergence in human subjects undergoing rotational acceleration using a binocular eye-tracking system.
BACKGROUND
This report describes the measurement of convergent eye movements and calculation of the spatial convergence point from the angular eye position data. These measurements were made in the dark while the subject experienced inertial motion aboard a centrifuge. This was an exploratory experiment with the goal of evaluating the eyes' convergence in the dark, and to see if this convergence point is dependent on inertial motion.


METHODS
The subject was rotated in the dark on NAMRL's Coriolis Acceleration Platform in Pensacola, FL. The pupil positions were tracked by two helmet-mounted infrared cameras connected to a computer-controlled data acquisition system. We used the position data to calculate the angles through which the eyes rotated, and then applied trigonometric principles to construct the line of sight for each eye for any instant in time. The intersection of these two lines of sight was the convergence point.


RESULTS
With the binocular eye-tracking system, we could accurately determine an accelerating subject's convergence point to within 10%, if the point was less than 1.5 m away from the subject. At convergence distances greater than 1.5 m, the angular movements of the two eyes became so small that determining a convergence point was difficult.
Fajardo
A B
AB
Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219, USA.
Luke
B L
BL
Grant
J W
JW
D000054:Acceleration; D002138:Calibration; D003290:Convergence, Ocular; D004867:Equipment Design; D005240:Feasibility Studies; D006801:Humans