Urine and blood tests can usually only detect substances consumed in the past two to three days. A new technique, devised by Iritech in San Jose, CA, screens for longer-term drug use-up to two weeks-by looking at eye response. A person looks into a binocular-like camera and is exposed to a flash of light. Software calculates how quickly the pupils shrink and recover, compares this response against pupil records stored in a database, and gauges within seconds whether the subject has taken drugs or alcohol during the past several weeks.

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