An Evaluation of Proximal Convergence by the Use of Infra-red Photography

Elaine Cornell, DOBA

Reg Mitchell, B.Sc., M.Sc, M.Ed., (Hons)

Convergence of the eyes was measured photographically in two situations:

i.         In normal illumination, at distances from 50cms to 10cms.

ii.         In the dark, by use of infra-red photography. The subjects were instructed to hold the target at the above distances and imagine that they were looking at it.

It was demonstrated that the measurements obtained in the light approximated well with the predicted hyperbolic curve, the formula C=2D being adequate enough to account for 98%of the variability in the measurements.

Measurements in the dark also resulted in this high degree of agreement with the theoretical curve. However, comparison of the measurements taken in the dark with those in the light showed that convergence response in the absence of visual clues is strong and is frequently in excess of the required convergence. It is suggested that this is due to proximal convergence which may play a greater role in the position of the eyes for near then has been demonstrated previously.