I wonder what the false positive rate is..

This sounds sort of hard to believe, but we are talking Malaysia:

Malaysia will soon begin using eye-scan machines in schools to detect drug usage among teenage pupils after reports that a large number of adult drug users begin their addictions while in school, media reports said yesterday.
Deputy Education Minister Noh Omar said the 200,000-ringgit ($53,333) machines should be able to detect signs of drug use within 24 hours by using light displays to measure eye movement.
A preliminary test of the eye scans is to be conducted next month at a school in
Kuala Lumpur, he said.

Moreover, things have already been just a tad regimented for Malaysian students:

Previously, the government had been conducting random urine tests on teenage students in schools.

Why hasn't at least a private school in Australia tried flying that one?

They also apparently start young in that country:

The government revealed Thursday that a total of 17.7 per cent of drug addicts polled in Kuala Lumpur had started their addictions before the age of 13 with morphine and heroine topping the list of favoured substances.
Authorities said Malaysia has more than 500,000 addicts, but health workers fear the numbers could be much higher.
Despite Malaysia’s tough drug laws, which prescribe a mandatory death sentence by hanging for drug trafficking, drug addiction continues to be on the rise.

I wonder how reliable these figures are. They have a strong smell of 'moral panic' abut them.