Almost half of students who had their eyes tested at Massey University are suffering headaches and vision problems - mainly due to looking at cellphones and computer screens for up to 12 hours a day.
The study of 70 students at the university's Palmerston North campus found that students were spending an average of 6.4 hours a day looking at mobile phones and other digital devices.
Many, such as accountancy student Megan Hislop, 19, said most of their study resources were now online, so they were both reading and writing on screens.
She estimates that she spends seven hours a day working on her studies on her laptop, plus about 10 hours a day checking her cellphone.
"When I get up I check the weather on my cellphone, I check Facebook and Snapchat and emails, and then go to university and look at projector screens," she said.
"By about lunch time I'm on my phone again, then on the computer for studying afterwards, and then the cellphone throughout all that process."
She has been prescribed glasses that have "a very slight prescription element" but are mainly aimed at reducing the "blue light" absorbed from cellphones, computers and television screens.
"My eyes took so much longer to focus, which led to them getting dry, and then I'd get headaches," she said.
"Initially I was thinking oh gosh it's going to be expensive to get glasses, but now that I've got them I can see the benefit of having them. I feel like I'm not so strained throughout the day."
The optometrist who did the study, Maile Tarsau, said teenagers were now having problems reading small print due to the blue light emissions from digital devices.
"Younger people these days are telling me they have problems seeing those types of things, when it used to be a 40- or 50-year-old that was complaining of those things," she said.
"We are talking teenagers here having trouble trying to keep up with things. It just happens a lot earlier."
Tarsau donated her time to test the Massey students for the Essilor Vision Foundation, a charity run by the French-based Essilor Group, the world's largest manufacturer of ophthalmic lenses.
The foundation registered as a charity in New Zealand last year and has done eye tests on 2800 children in low-decile primary schools, finding 31 per cent with previously undiagnosed vision issues.
Although the Massey students self-selected by volunteering to have their eyes tested, Tarsau said the finding that 45 per cent had undiagnosed eye problems confirmed the widespread effects of increased use of digital devices.
"Tired eyes, watery eyes, gritty eyes and headaches are very, very common," she said.
Even major problems such as macular degeneration and cataracts, which used to affect people in their sixties and seventies, are now affecting younger people.
Tarsau said her practice, Visique in Palmerston North, now gave all clients the option of adding filters to reduce blue light for an extra cost of about $20 on top of all prescriptions.
The Essilor Vision Foundation said it planned to screen more students at Massey and other NZ tertiary institutions later this year.