Eye Trick

American Optical Co. (Southbridge, Mass.) last week announced a new trick to detect fakers who claim eye injuries, expected the trick to be of interest to insurance companies and industrial corporations. The gadget makes use of polarized light, which is light filtered so that it vibrates in only one plane. If light filtered through a polarizing crystal encounters a second crystal whose cleavage plane* is turned perpendicularly, it cannot get through. But if the second crystal is rotated until the cleavage plane is parallel to the light waves, the light is then transmitted.

For a century scientists have been polarizing light with small natural crystals. Lately a synthetic polarizing material called Polaroid has been developed which can be fabricated into large sheets. In American Optical Co.'s gadget, light from an illuminated test chart first passes through a disk of Polaroid. The person being tested looks through a pair of polarizing lenses, one vertical, one horizontal. By rotating the first disk, the examiner can cut out the vision of either eye at will, so that the subject does not know with which eye he is seeing. It is thus impossible for him, if he is faking an injury in one eye or the other, to give a reading which is consistent with the examiner's manipulations.

*The molecules in a crystal are arranged in regular rows. The cleavage planes are tiny gaps between these rows, like the gaps in a picket fence, through which the light passes. If the planes are vertical, for example, only vertically vibrating light will pass through.

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