New Zealand has the highest rate of melanoma in the world, but Melanoma New Zealand says more research needs to be done to figure out why some people lose their eyes to it.
John Riley had no idea that a routine eye test would show he needed to have his eye removed.
"The optometrist said, 'Would you like a photo of the back of the eye because it give a bit more detail', and I said, 'Yes, why not', and boom there it was," he told Newshub.
"[There was] this big green thing across my eye and the optometrist was pretty shocked because he didn't know what it was either."
Initially, Mr Riley thought it must've been a scratch. But a few days later, he was told it was a tumour and after more tests, it was found to be ocular melanoma, which attacks the eyes.
"It had pretty much taken up close to three-quarters of my eye and I was getting little black flashes in my eye."
That was two years ago and if he hadn't caught it then, in the early stages, he would've lost more of his sight, and it could've spread.
"it accounts for less than 5 percent of melanomas in New Zealand," Melanoma NZ's Dr Rosalie Stephens told Newshub.
"We think it's a distinct disease from the melanoma that comes from the skin."
More than 4000 Kiwis are diagnosed with melanoma every year and usually, it's caused by extensive UV exposure.
But in Mr Riley's case, it's not clear what caused it and he says he never got a definitive answer.
Because it's so rare, little is known about this form of cancer.
"We never have the resources in a public health system to do the research that's required," Dr Stephens said.
"It certainly does seem to affect people with fair skin and light eyes more. So it is possible that sun exposure has some role to play in causing it."
These days, Mr Riley always wears sunglasses outside to protect his remaining eye.
"You don't realise how precious they are, until you lose them," he said.
All Kiwis know to protect their skin from the sun but his advice is to protect your eyes too.