As the rush to grab a pair of eclipse viewing glasses before they sell out ahead of the April 8 total solar eclipse heats up, experts so far have welcome news for those worried about potential glasses' scams.

"We have not seen any glasses or heard of any glasses that are demonstrably unsafe," Rick Fienberg, the project manager of the American Astronomical Society's solar eclipse task force, told USA TODAY.

Gazing at the bright rays from the eclipse without protective eyewear can cause serious damage the retina of the eye, so wearing a pair of safe glasses is paramount. With online platforms like Amazon listing thousands of eclipse viewers, fears of fake or counterfeit glasses have grown.

While Fienberg isn't worried about a flood of unsafe glasses on the market, some glasses for sale display false or misleading information on their packaging or design.

"We do see glasses coming from China that have printing on them that say they're made in the U.S. or that they are made by one of the American manufacturers," Fienberg said.

When in doubt, buyers should refer back to the list of official sellers and manufacturers maintained by the AAS, which communicates directly with sellers and manufacturers and checks test reports. Manufacturers need to have their glasses tested independently at two top labs in the U.S. to secure a spot.

The list includes well-known North American manufacturers like American Paper Optics, as well as several large grocery and retail chains in the U.S. like Walmart, Lowe's, and Kroger.

NASA has also shared an easy method to vet eclipse glasses at home.

Buyers should put on their glasses and look at a bright light, like a flashlight. If the light is "extremely dim," or doesn't appear at all, the glasses are safe, Susannah Darling, of NASA's Goddard Space Flight Center, said in an instructional video. Viewers should be able to see the filament of the lightbulb, not the glow surrounding the bulb.

Glasses can only be safely tested with a home lightbulb, and should never be tested with the sun, Darling said. Eclipse glasses with scratches or damage are not safe to use.

More:What does a total solar eclipse look like? Photos from past events show what to expect in 2024

What is the standard for eclipse glasses?

The current international standard for solar eclipse viewers, called ISO 12312-2 after the International Organization of Standardization, was adopted nine years ago, according to the AAS.

"Before 2015, there were a hodgepodge of standards for solar viewers," Fienberg said. After gaining signatures from almost every country in the world, ISO 12312-2 "became the global standard for safety for viewers meant to be used for direct viewing of the sun," he said.

The new standard also changed NASA's official guidance, which previously "insisted that the only safe way to observe an eclipse was through pinhole projection or optical projection, no direct viewing at all," Fienberg said.

Amazon recalls eclipse glasses ahead of 2017 eclipse

But problems with verifying the standard emerged in the leadup to the 2017 solar eclipse. As eclipse viewing supplies ran short, the market was suddenly flooded with Chinese-manufactured eclipse viewers primarily for sale on Amazon that claimed on the label to be ISO certified without solid proof.

"Anybody can print that on anything," Fienberg said. "It doesn't mean it's true."

In the weeks before the eclipse, warnings of counterfeit eclipse glasses set off a panic that saw some people dump their glasses and miss out on the entire experience, Fienberg said.

More:Total solar eclipse will be visible to millions. What to know about safety, festivities.

Meanwhile, Amazon issued full refunds to customers who bought some eclipse glasses that the shipping giant determined were not up to "industry standards."

Fienberg got involved when a certified vendor reached out because Amazon had taken down their listings.

"I got this panicked phone call from a vendor I've known for years saying, all our stuff just got pulled from Amazon, and apparently they're pulling everybody," Fienberg recalled.

Fienberg said he contacted Amazon directly and persuaded the company to put the products back up, but he now fears some vendors with sketchy documentation for their eclipse glasses might have also ridden the wave and had their products relisted.

Fienberg believes some vendors submitted documents as proof of certification to Amazon in the years since that look legitimate to an untrained eye, but are missing quantitative results of a safety test. He receives his own share of similarly fraudulent documents from manufacturers requesting a spot on the AAS list.

Fienberg said "countless" sellers on Amazon don't provide evidence that their glasses come from an approved manufacturer. Although many listings include the same pictures of the ISO 12312-2 test reports as manufacturers on the list, AAS surveyors have no way to tell.

"I'm still seeing people write in and say, 'I'd like to get on your list. Here's the certification from my manufacturer in China,' and it's the same bogus report that I've seen 20 times already," he said.

A spokesperson for Amazon told USA TODAY, "We ensure our selection meets industry-accepted standards, and we develop innovative tools to prevent unsafe products from being listed. We continuously monitor our store, and if we discover a product was undetected by our automated checks, we address the issue immediately and refine our controls."

More:How long will the solar eclipse darkness last in your city? Explore these interactive maps.

Tests show most glasses are safe

In hindsight, alarm about the Chinese-made glasses might have been overstated, Fienberg said. Testing after the fact revealed that the majority of the glasses, including from the Chinese manufacturers, seem to be safe.

"We've seen a few, slight outliers," he added. "They fail to meet the standard by a small amount."

Those tests led AAS regulators to relax their safety requirements ahead of this year's eclipse. Fienberg and two colleagues also submitted a proposal to loosen the international standards that he hopes to see passed by next year.

Although the AAS hasn't encountered any severely faulty glasses, Fienberg still recommends against buying any old pair off of Amazon.

"There is no way for an ordinary citizen to confirm that eclipse glasses are safe," he said. "We have no reason to suspect that the stuff is unsafe, but we don't want to promote it without certainty."

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at [email protected]. Follow her on X @CybeleMO.