He says it's also generally unwise to put any foreign body in the eye. A concussive blow, he said, could drive it inward.
"Why would anyone want to tempt changes in vision or damage to their vision if it's not necessary?" Rizzuto asked. He's unaware of any other eye jewelry implants in the U.S.
"This behavior is very risky both for the patient and the provider," Glenda Secor, the American Academy of Optometry's communications chair, told U.S. News.
"Risks of complications for the patient can vary from mild to severely sight threatening depending upon the outcome," Secor says. "The choice to have a procedure that has potential significant risk – when safety and efficacy has not been determined – is discouraged."
Chynn says his critics tend to be conservative and timid. He says there are no serious risks from implanting the jewelry.
"I'm not exactly going to do a procedure that has even a tiny, tiny risk of visual loss just to put jewelry in the eye – that would be crazy," he said.
Updated 11/26/13: An update was appended to the beginning of this article.