Whether passing someone on the highway or cruising at 30,000 feet in a plane, several times a day we entrust our health -- and sometimes our lives -- to the judgment of others. Alcohol or drug abuse can betray that trust, putting us in danger. Ross Campesi, president of Labor Station National Inc., provides labor for construction, for warehousing and, occasionally, for the US Longshoreman and Harbor Workers. To test employees' suitability for employment, he previously relied on urinalysis. "There were a lot of tricks being played in that game," he said. In one memorable incident involving a male employee, the test positively identified him as being pregnant. Campesi now uses a photonic device called SafetyScope, which determines intoxication by monitoring tiny changes in the eye. SafetyScope gauges intoxication by using a CCD camera to measure eye movement and pupil changes. The device provides instantaneous pass/fail results, so users can save money by limiting urinalysis to verifying SafetyScope "failure" results. Eye Dynamics Inc. developed the instrument, which measures the eyes of the subject in a dark-field environment using miniature 512 x 512-pixel CCD cameras and off-the-shelf video equipment. The test administrator instructs the subject to follow a point of light that moves across a horizontal plane. The administrator sees an image of the eye in monochrome. Intoxicants break down a person's ability to smoothly track an object, producing a jerking movement, called nystagmus, in the horizontal plane. Nystagmus typically occurs in response to central nervous system depressants. Another measurement involves watching the eye at the periphery of vision. Alcohol tends to produce large-amplitude tremors that persist for at least four seconds. If the instrument indicates the possibility of intoxication, urinalysis is used to verify the suspicion. This saves the expense of performing a urinalysis on every employee. Although he didn't want to give precise dollar figures, Campesi said that the device had reduced his cost of testing employees by 75 percent. Another benefit of SafetyScope is that the result is specific to the individual. Campesi said he can run the SafetyScope 24 hours a day, and the results are instantaneous. "It certainly is a vast improvement," he said. "It gives me the edge over my competition.