The Great North American Eclipse of April 8 will first be visible from land in Mazatlán, Mexico, and from there will travel northeast across the United States and up to Newfoundland, Canada. The path of totality, where the eclipse is fully visible, will span a width of approximately 62 to 71 miles, but a partial eclipse will be visible across much of the continent to varying degrees. This fortuitous route means that upwards of 31 million people will have the opportunity to witness the remarkable event firsthand, but that has the experts worried.

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Ronald Benner, president of the American Optometric Association, warns of the dangers associated with viewing an eclipse without proper protection. Solar retinopathy, a condition resulting from intense light exposure, can cause serious and often permanent damage to the retina, the sensitive layer of cells at the back of the eye. The retina plays a critical role in the process of vision, converting light into neural signals that are then sent to the brain through the optic nerve.

The problem is that eclipses create a false sense of security. We normally don’t stare up at the Sun because it’s really uncomfortable, but this isn’t the case during an eclipse, when the Moon blocks much the Sun. It’s easy to get the mistaken impression that there’s hardly any light that could be damaging our eyes. This misconception leads many to remove their eclipse glasses, not realizing when the full intensity of the Sun will resume—a particularly risky behavior, according to Benner.

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The risks are particularly concerning for children. Parents may be keen to have their children witness an eclipse but to guide and control them effectively. “Where it’s really scary to me is when parents take their children out, because they want their children to experience it. But if you’re trying to manage three, four, five kids at the time, and making sure the kids all follow the instructions of what they’re supposed to do, children don’t always understand the consequences.”

The American Academy of Ophthalmology offers slightly different advice, claiming that observers can safely view the Sun without protection only during a total eclipse when the Moon completely blocks the Sun’s bright face, i.e. during totality. Once the Sun begins peeking out, observers should put their eclipse glasses back on to watch the remaining partial phase of the eclipse. However, it is advisable to follow the advice of experts like Ronald Benner, who urges making the experience positive and safe by wearing proper eye protection throughout the entire event.