How to Safely View a Solar Eclipse

On Aug. 21, all eyes will be on the total solar eclipse as it makes its way along a 70-mile-wide swath of the United States from Oregon to South Carolina. The last time a total solar eclipse was visible in the United States was 1979, well before the dawn of cell phones and the now-ubiquitous selfie.

“Many people will think it’s safe to take a selfie with the eclipse in the background because they aren’t looking directly at the sun,” says Tongalp Tezel, MD, a retina expert at Columbia University Medical Center. “What they may not realize is that the screen of your phone reflects the ultraviolet rays emitted during an eclipse directly toward your eye, which can result in a solar burn.”

According to Dr. Tezel, Sir Isaac Newton suffered retinal damage after looking at the reflection of an eclipse in the surface of a pond—the archaic equivalent of the cell phone screen. Viewing the eclipse through a telescope can also damage the retina, as Galileo himself learned, because the device magnifies the sun’s harmful ultraviolet rays.

Avoiding Retinal Sunburn

A solar eclipse occurs when the moon moves directly between the sun and the earth, blocking all visible light except for the rays from the outer atmosphere of the sun, known as the corona. Normally, you can only glance at the sun with the naked eye for a few seconds before your eyes start to well up. But when an eclipse casts its shadow, and your eyes are no longer wincing at the light, you may be tempted to gaze at this phenomenon for a long while.

It is safe to view the sun briefly—for a minute or two—only while the sun is completely eclipsed by the moon. However, it is a mistake to stare at the sun during any other phase of the eclipse, even if there is significant cloud coverage, says Dr. Tezel. It’s precisely when you can’t feel the burn that the sun’s ultraviolet rays can cause considerable retinal damage.

And while sunglasses may be the perfect way to protect your eyes on a sunny day, they can actually cause harm during a solar eclipse. “Because sunglasses make everything appear darker, your pupils become enlarged, letting in more of the harmful rays,” says Dr. Tezel, who explains that the safest way to view the eclipse is by wearing a pair of ISO 12312-2-certified solar glasses that are specially designed to filter out the sun’s harmful ultraviolet rays.

When to See the Doctor

Ignoring this advice can result in blurry vision or even vision loss along with color perception anomalies and blind spots. Although these symptoms may partially recover in time, longer-term exposure that can occur during an eclipse can lead to permanent loss of central vision from damage sustained by the light-sensitive rod and cone cells in the retina. See an ophthalmologist immediately if you experience vision loss and visual distortions.

Dr. Tezel is the Chang Family Professor of Ophthalmology and head of the Retina Service in Columbia University’s Department of Ophthalmology.