Total Solar Eclipse 2017: What Happens to Your Eyes If You Look Directly at the Sun?

the sun
An X3.1-class flare erupting from the sun on October 24, 2014. If you don’t use proper protection when viewing the upcoming total solar eclipse, you could burn your eyes. NASA/SDO

A total solar eclipse will plunge parts of the U.S. into darkness on August 21, as the moon passes directly in front of the sun. The event, which Bill Nye, the so-called Science Guy, calls "exciting and profound," will be watched by millions of people across the nation, as its path runs from Oregon to South Carolina.

To help watch the solar eclipse safely, NASA and other experts have published tips and guidelines. But what happens if you do look directly at the sun? Dr. Christopher Quinn, the American Optometric Association's (AOA) president, tells Newsweek about the damage you can do—and how to avoid it.

What actually happens to your eyes if you look directly at the sun?

solar eclipse
A solar eclipse is seen from the beach on Indonesia’s Ternate island in 2016. An intricate dance leads to a total solar eclipse. Beawiharta Beawiharta/Reuters

The AOA strongly recommends using special-purpose solar filters or other ISO-certified filters, such as "eclipse glasses" or handheld solar viewers, to view the uneclipsed or partially eclipsed sun [outside the 70-mile path].

If your eyes are exposed to excessive amounts of ultraviolet radiation over a short period of time, such as during the eclipse, you could experience photokeratitis, essentially a sunburn of the eye. Symptoms include red eyes, a foreign body sensation or gritty feeling in the eyes, extreme sensitivity to light and excessive tearing.

Unless you take proper precautions, looking directly at the sun during a partial eclipse can also cause solar retinopathy, which can result in permanent damage to your eyes. This is caused by light from the sun flooding the retina on the back of the eyeball. This exposure to solar radiation on the retina causes damage to its light-sensitive rod and cone cells by igniting a series of complex chemical reactions within the cells.

Related: Total solar eclipse—where to buy glasses and how to make a homemade viewer

total solar eclipse
Lebanese women use special sunglasses to watch the partial solar eclipse in downtown Beirut on March 29, 2006. Joseph Barrak/AFP

How long would you have to look at the sun to go blind?
Length of time doesn't matter. Even looking directly at the sun for a short duration can actually burn the retina. Eye damage, including solar retinopathy—a serious injury in which the eye's retina is damaged by solar radiation—and photokeratitis can all occur while viewing an eclipse, and injuries can be temporary or permanent. If one is worried that accidental exposure has occurred, they should visit a local doctor of optometry.

Just a few seconds can cause damage.

Is there normally a spike in eye-related injuries after a solar eclipse?
It's been 99 years since a coast-to-coast eclipse. I think that people will see the advice and professional guidance widespread throughout the media and will hopefully take our advice into consideration and take the necessary precautions while viewing the eclipse.

What should people do if they think they have damaged their eyes during the eclipse?
If you are exposed to the sun during an eclipse and think there is potentially something wrong, it is best to visit a doctor of optometry immediately to ensure there is no serious or permanent damage. Since damage can occur without any sensation of pain, it's better to be safe than sorry.

What is the best way, in your professional opinion, of watching the eclipse?

solar eclipse
Map showing the U.S. path of the total solar eclipse on August 21. Wolfgang Strickling/CC

The only safe way, and therefore the best way, to directly view the eclipsed or partially eclipsed sun [outside the 70-mile path] is through special-purpose solar filters or other ISO-certified filters, such as "eclipse glasses" or handheld solar viewers.

Also, be sure to follow any instructions printed on or packaged with the filter, and inspect your filter before use to ensure it isn't damaged or scratched. The AOA encourages ordering solar eclipse glasses in advance and recommends referring to the American Astronomical Society's site for a list of manufacturers.