The upcoming total solar eclipse promises to be a once-in-a-lifetime experience, but viewing the celestial spectacle without proper eye protection can cause irreversible damage. Here’s what experts say about the risks and how to watch safely.
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. (Be sure to check out our eclipse viewing guide here.) 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.
The risk of permanent eye damage from looking at a solar eclipse
Watching a solar eclipse is a rare and stunning event, but it poses significant risks to our eyes. 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.
“People want to go out and watch it, but there’s some bad information out there about how to watch the eclipse,” Benner explained to me. Some of the dangerous advice includes wearing dark sunglasses, doubling up on dark sunglasses, or using a welder’s mask. “But none of that’s true,” he cautioned.
When selecting eclipse glasses or hand-held solar viewers, it’s essential to ensure they adhere to the global standard ISO 12312-2 and clearly display this certification for safe and reliable use. “Solar filters that provide safe, comfortable, unmagnified views of the Sun generally transmit between 1 part in 100,000 (0.001%) and 1 part in 2,000,000 (0.00005%) of its visible light,” explained Rick Fienberg, project manager of the American Astronomical Society Solar Eclipse Task Force, in a statement. “Such filters are at least 1,000 times darker than even the darkest sunglasses.”
Regular sunglasses, even when doubled, or welder’s masks, don’t come remotely close to these filtration levels.
False sense of security
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.
The retina, a very sensitive part of our eye, is at risk during these events. “The retina is an extension of the brain—it’s a pure neural network back there. And when we typically look at light, we get a chemical reaction that turns into an electrical reaction that sends a signal to the brain,” he explained. Unfortunately, this delicate structure can be irreparably harmed by intense light. Incoming rays can “burn out” this tissue, leading to inflammation and impaired function of the rods and cones, which are crucial light-sensing cells in the retina. This damage can be permanent, as these cells may die off, especially affecting color vision if the cones are damaged.
According to a 2013 study published in Case Reports in Ophthalmological Medicine, solar retinopathy often goes unnoticed initially because its symptoms are subtle and can easily be overlooked. This makes diagnosis challenging, as the damage from light or heat doesn’t always appear severe at first. Despite its deceptive mild presentation, it’s a serious condition for the eyes. And unlike skin or the corneal epithelium, which can regenerate, the retina’s damage doesn’t show immediate symptoms, often leading to a delayed realization of permanent vision loss or changes such as distorted color perception.
“Most people who have solar retinopathy don’t really know when they got it,” Benner said. Damage isn’t instantly painful, leading to delayed awareness. He likened it to a sunburn where it’s not clear that damage has been done until several hours later. When medical help is sought, doctors might identify inflammation and assess potential nerve tissue recovery, but the neural network of the eye might only partially recover, if at all. Over time, this unresolved damage can lead to scarring, resulting in visual impairments like “holes” in vision.
The most severe consequence of solar retinopathy is the loss of central vision. Benner likens this to creating a hole in an old photographic negative with a paper hole punch. Other effects include permanent changes in color perception, distortion of vision, light sensitivity, and headaches.
“Once that tissue has been damaged, it’s up to the body to try to repair it. There is no medication, there is no treatment, there are no workarounds. And that’s why we take this so seriously, because once it’s done, it’s done,” he said.
‘Not worth the risks’
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.” Indeed, these guidelines are complicated enough for adults, let alone children.
A significant concern is for those outside the path of totality who may underestimate the harm of looking at the eclipse without proper protection. For those observing the eclipse from within the path of totality, they too might not fully grasp the potential hazards, Benner warned. “It’s challenging to determine at what point the sunlight becomes harmful. Therefore, avoid taking any risks,” he said. “If you’re keen on observing the eclipse closely, it’s safer to watch it on TV or online.” He urges making the experience positive and safe, rather than a regrettable one, and advises against observing the eclipse with unprotected eyes even during totality.
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.
That said, Benner’s advice is clear and sensible: “Don’t let it become a negative experience that you have to live with for the rest of your life.” So enjoy the upcoming eclipse, but remember to do so safely by using proper eye protection without risking your vision. And remember that critical string of letters and numbers: ISO 12312-2.
A version of this article originally appeared on Gizmodo.