Sun photo

This afternoon, millions of Americans will head outside to witness the total solar eclipse cutting across our country. Luckily, most people who have planned for this event have likely taken the necessary precautions by purchasing a pair of legitimate eclipse sunglasses. By doing so—and by wearing them properly—they’ve given themselves the best chance at avoiding a dangerous side effect to eclipse viewing: solar retinopathy.

This solar eclipse is pretty special, but that does not make it OK to look directly at the sun. No, not even this once. Never stare directly at the sun, even for the 2-3 minutes the moon is, for the most part, blocking it.

How is the sun so damaging? Well, we see images because photoreceptors, cells also known as rods and cones located at the back of the retina, convert the light into electrical impulses that the brain uses to determine the image we see. But when strong light, like the sun’s rays, hits our eyes, a series of chemical reactions occur that damage and often destroy these rods and cones. When this happens, which is known as solar retinopathy, our eyesight becomes blurry. Sometimes, if the damage is too great in one area, our vision can be completely impaired.

On a typical bright day, you almost never have to worry about solar retinopathy. That’s because our eyes have natural mechanisms to ensure that not too much light gets in. When it’s really bright outside, our pupils get really tiny, making the space for the sunlight to hit your photoreceptors smaller. That’s why your eye doctor gives you special dark sunglasses to wear after getting your pupils dilated.

When you stare at the sun directly, though, your pupils’ shrinking power isn’t enough to protect your peepers.

Along with your pupils shrinking, your eyes also have another defensive mechanism. When we look at something bright, we tend to blink our eyes, something known as the corneal or blink reflex. This also prevents us from staring at anything too damagingly bright. But during a solar eclipse, before it has reached totality, the moon is still partially blocking the sun. That means it’s blocking some of that intense light, and it’s a lot easier for us to look up at the sun without blinking. But that doesn’t mean you should. Even that tiny sliver of sunlight is too intense for our sensitive photoreceptors.

So if you do want to watch the eclipse with your own two eyes, wearing those special sunglasses is crucial as they block the sun’s rays enough, allowing you to see the eclipse and not burn your eyes out.

Unfortunately, if you do practice unprotected sun gazing, you probably won’t know the effects of your actions until the next morning, when the damage to your photoreceptors has kicked in.

While solar retinopathy is extremely rare, it is by no means unheard of. If you search the term in medical journals, you’ll find case reports after almost every popular solar eclipse. Let’s try really hard to do better this time, eyeball-havers.

You don’t have eclipse glasses? Check out our live stream of the eclipse here, or else try to whip up your own eclipse projector.