Some of the students were from remote areas where it takes hours to reach an eye clinic and travel is often unaffordable.
"They learn about the impact of diabetes, some public health work, refraction which is testing eyes for glasses and theoretical work. They were learning refraction while I was there so I was helping them learn and passing on tips about testing eyes.
"When they finish the course they go back to their homes and become eye-care workers for their communities."
Tonga currently has no eye surgeon but a nurse on the course would go back and provide some level of eye care in the country, Russell said.
A simple eye test could make a huge difference to people's lives.
"We had one young 9-year-old whose existing glasses were lost over a year ago. She had astigmatism in each eye so school had been a challenge for her. Between the nursing student and myself, we got her an accurate refraction, chose a nice set of frames and once the glasses arrive in Suva from our Specsavers lab she'll be back to seeing well at school.
"A bunch of people just need reading glasses but they can't access clinics."
It was Russell's fourth charity work trip but the first time he has been involved in training. On the previous trips he was testing eyes and providing glasses.
"Being able to see where the money goes means you can talk to people here about it. I've spoken to Rotary about what I had been doing and St Oswald's Church was already fundraising for Fred Hollows so I had the opportunity to talk to them.
"That's really cool - in a community like Whanganui you have the opportunity to go and talk to people about it."
He has also run a marathon to fundraise for the Fred Hollows Foundation and will take part in October's Auckland Marathon to raise money.
Russell is the co-owner of Specsavers Whanganui. While he was in Fiji, the Whanganui branch donated $5 from every eye exam to the Fred Hollows Foundation NZ, raising $550.