NASA is warning consumers to beware of unsafe, counterfeit glasses sold for viewing the Aug. 21 eclipse.
Only glasses marked ISO 12312-2 are recommended.
Some counterfeit glasses are simply marked with ISO.
"It now appears that some companies are printing the ISO logo and certification label on fake eclipse glasses," the space agency said.
Some sellers are displaying fake test results on their website to support a bogus claim of compliance with the ISO safety standard, NASA said.
Experts warn that looking at the sun without protection or inadequate protection, such as using sunglasses, can cause lasting vision problems.
"The only safe way to look directly at the uneclipsed or partially eclipsed sun is through special-purpose solar filters, such as 'eclipse glasses' ... or hand-held solar viewers," according to NASA. "Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the sun; they transmit thousands of times too much sunlight."
NASA recommends purchasing the glasses from vendors supported by the American Astronomical Society.
Detailed safety information and a link to reputable vendors can be found on nasa.gov.