Samuel Woodhead, 18, disappeared on Tuesday after he set out for a jog from a cattle station in Queensland, Australia.
However, the chance discovery of packets of lenses in his rucksack apparently sustained him in the scorching heat.
These had previously been placed in the bag by Mr Woodhead's father, Peter.
The teenager was said to be a little sunburned following his ordeal, but was hydrated and otherwise well.
His relieved mother Claire, 54, described how her son survived in the 40C heat. She said: "His father had packed boxes of contact lenses in his rucksack in an outside pocket and he'd forgotten to take them out.
""He's lived on the fluid that the contact lenses – you know the little packs of contact lenses? He's lived on those packs of contact lenses for three nights."
Relatives said the teenager, a keen long-distance runner, owed his life to rescue workers who launched a helicopter search of the desolate region after he was reported missing from Upshot Station, near the town of Longreach, on Tuesday.
Mrs Woodhead, who travelled to Australia, said: "I've spoken to Sam on the phone and I'm flying out to Longreach."
She added: "I'm very, very relieved indeed. I've just had the worst three days of my life, and when I got the message from the pilot on the plane), I just cried."
The former Brighton College student, from Richmond upon Thames, in Surrey, was taken for a medical assessment before being transferred to a hospital in Longreach.
News of his survival came as it emerged another man who went missing in the same area for a shorter period of time had died of dehydration.