Millions of people are expected to watch the total solar eclipse that will cross North America next week, with some locales so worried about hordes overrunning the best viewing sites that they've declared states of emergency ahead of the sky-darkening event.

But lawsuits filed in 2017 — shortly after the annular "Eclipse Across America" created a dramatic ring of fire around the moon — provide a stark warning for those who plan to turn their gaze to the heavens on Monday, April 8.

Plaintiffs in at least three states said they suffered a range of injuries because sustandard solar eclipse glasses they wore on Aug. 21, 2017, failed to protect their eyes from the sun's damaging rays.

In their suit, Thomas Corey Payne and Kayla Harris of Charleston, South Carolina, said that shortly after watching the eclipse, they "began to experience pain and discomfort, headaches, eye watering and other symptoms."

"Thereafter, both Plaintiffs began to see dark spots in their line of vision, suffered vision impairment, including blurriness, a central blind spot, increased sensitivity, changes in perception of color, and distorted vision," according to the complaint.

Steven and Susan Levine of Boca Raton, Florida, said they were left with "headaches and other physical injuries, including temporary and/or permanent vision loss and/or impairment."

Dr. Purnima Patel, clinical spokesperson for the American Academy of Ophthalmology, told HNGN that looking at an eclipse without proper protection can cause burning of the retina known as solar retinopathy.

"The damage can happen in a matter of seconds," Patel said in an email. "Symptoms may not appear until a few hours after exposure and include blurry vision and blind spots in one or both eyes."

Patel added: "Unfortunately, there is no treatment for solar retinopathy."

The various plaintiffs said they either bought their eclipse glasses from Amazon or, in the case of Kendall and Kim Heise of Castle Rock, Colorado, got them for free by purchasing eyeglasses at a local optical store.

After their suit was filed, defendant Europtics told the Denver Post that it bought the eclipse glasses from Amazon.

In each case, the plaintiffs alleged that their eclipse glasses didn't meet an international standard known as ISO 12312-2, which covers non-prescription lenses or filters used for "direct observation of the sun, such as solar eclipse viewing."

It ensures that eclipse glasses are "about 100,000 times darker than ordinary sunglasses and block nearly all visible light as well as all infrared and ultraviolet light," according to the nonprofit Planetary Society.

About a week before the 2017 eclipse, Amazon recalled some of the eclipse glasses sold on its site and offered refunds to buyers, saying it couldn't confirm the products were safe to use, PBS reported at the time.

On Monday, an Amazon spokesperson told HNGN that the company has since "implemented new controls" to ensure all eclipse glasses sold on the site comply with ISO 12312-2 and that "if we discover a product was undetected by our automated checks, we address the issue immediately and refine our controls."

On its website, NASA says eclipse glasses "ought to comply with the ISO 12312-2 international standard" but notes that it "does not approve any particular brand of solar viewers."

The nonprofit American Astronomical Society Solar Eclipse Task Force, however, has compiled a list of retailers that sell "ISO-compliant safe eclipse glasses and/or handheld viewers."

On March 22, it also issued a warning about how "counterfeit and fake eclipse glasses are polluting the marketplace."

"With millions of North Americans only now becoming aware that a solar eclipse is imminent and seeking to get their hands on eye protection, it is critical that everyone understand how to spot unsafe products," the AAS said.

Although the lawsuits over faulty eclipse glasses were filed as class-action complaints, none were certified to cover anyone other than the named plaintiffs and none went to trial.

The South Carolina case was dismissed and the claims were sent for arbitration, while the ones in Florida and Colorado appeared to have been dismissed following settlement deals.

Lawyers on both sides didn't return requests for comment or couldn't be reached by HNGN on Monday.