Functional difficulties resulting from traumatic anisocoria.

An abnormal mydriasis of the pupil may be present after blunt contusion of the eye. Pro~ longed mydriasis indicates partial or complete rupture of the iris sphincter and may he permanent. 1 Anisocoria resulting from unilateral mydriasis may be associated with visual difficulties. Difficulties may be expected at nearwork because of the reduced depth of focus of the dilated eye. Other difficulties may result from the different amount of light entering each eye. This difference can distort depth perception of moving objects in a manner similar to the distortion demonstrated by the "Pulfrich phenomenon."2 Increasing the pupil size beyond 2.5 mm increases optical aberrations, thereby decreasing the depth of focus of the eye. The depth of focus depends also on the distance of the target from the eye: the closer the target is to the eye the smaller is the tolerance of the eye to distance changes. Thus, anisocoria that will cause little difficulty for distance vision may result in blurring of the image in the dilated eye at near, simulating unequal accommodation. Different amounts of light entering each eye have an effect on depth perception known as the "Pulfrich phenomenon." If a pendulum bob oscillating in a frontal plane is viewed with a neutral density filter in front of one eye, the bob appears to move in an elliptical path. It seems to be nearer the observer when moving in one direction and further away when movement is in the opposite direction.2 The illusion is caused by the increased latency of impulses from the eye covered with the dark filter_ If the filter is in front of the right eye, the bob will appear to rotate counterclockwise; that is, on its swing from right to left it will appear further from the