Solar eclipse: Dangers to avoid while watching

Eye-care and astronomy experts are cautioning solar eclipse watchers to protect their eyes with specialized solar filters, handheld solar viewers or eclipse glasses.

Eye-care and astronomy experts are cautioning solar eclipse watchers to protect their eyes with specialized solar filters, handheld solar viewers or eclipse glasses.

People in Canada's eastern provinces and parts of the United States and Mexico will have the chance to witness a rare total solar eclipse on Monday, April 8.

Eclipse glasses, and other safe solar viewers, use special filters made of black polymer or aluminized polyester to reduce the intensity of the sunlight. They block virtually all light and are thousands of times darker than regular sunglasses, according to NASA and other astronomy experts. People should use International Organization for Standardization’s certified glasses, labelled ISO-12312-2, which meet international safety requirements.

Dr. Shaina Nensi, vice-president of the Ontario Association of Optometrists in Toronto, recommends people get their eclipse viewers or glasses from the list of suppliers provided by the American Astronomical Society.

"If there are scratches or dents on them, then there's a chance the protective properties could've decreased," she said in a phone interview with CTVNews.ca.

The solar filter or glasses should only allow users to see the sun or light equally bright as the sun, not ordinary objects. "If you can see ordinary light through eclipse glasses or filters, then they're not safe and put you at high risk of damaging your eyes," Nensi said.

Eclipse glasses should fit snugly enough that wearers can shake their head without them falling off, according to Robert Cockcroft, assistant professor at the department of physics and astronomy at McMaster University in Hamilton, Ont., and secretary of the Canadian Astronomical Society. People who wear prescription glasses should make sure they fit underneath.