Using eye movement to detect lies contrasts with polygraph testing. Instead of measuring a person's emotional reaction to lying, eye-tracking technology measures the person's cognitive reaction. To do so, the researchers record a number of measurements while a subject is answering a series of true-and-false questions on a computer. The measurements include pupil dilation, response time, reading and rereading time, and errors.
The researchers determined that lying requires more work than telling the truth, so they look for indications that the subject is working hard. For example, a person who is being dishonest may have dilated pupils and take longer to read and answer the questions. These reactions are often minute and require sophisticated measurement and statistical modeling to determine their significance.[...]
Besides measuring a different type of response, eye-tracking methods for detecting lies has several other benefits over the polygraph. Eye tracking promises to cost substantially less, require one-fifth of the time currently needed for examinations, require no attachment to the subject being tested, be available in any language and be administered by technicians rather than qualified polygraph examiners.
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The only way to go someway towards knowing someone is lying is to know what body-language they used previously whilst lying. Even this will never-ever be 100% right.
I suffer from a form of dyslexia, that makes me slow, and my eyes not to stay still - that means that I'd be guilty of lying - according to this method - even if I told you that earth circles the sun, and that I was born on the planet Earth.
You can't hide your lyin' eyes.
Saying a person who is being dishonest MAY have dilated pupils means that someone may exhibit the same reaction while being honest.
Using statistical modeling means that they can only state the PROBABILITY that someone is lying, not that a person is CERTAINLY lying.
Until there is a way to actually read someone's thoughts, any kind of polygraph or lie-detector will not provide any useful data (meaning it won't be acceptable as legal evidence).
Actual, incontrovertible evidence will always be preferable to interrogating human beings, who are notoriously bad at remembering things accurately.