When a total solar eclipse comes to the Dallas-Fort Worth area on April 8, and the moon starts to cover the sun in the sky, it may feel safe to sneak a peek without eclipse glasses. But experts say that staring at the sun for as little as five seconds can damage your eyes. Look longer, and that damage could become permanent.

Here's why it's worth looking into the many safe and inexpensive ways to protect your eyes as the eclipse draws closer.

What happens when we look at a solar eclipse?

Light enters the front of the eye and is focused onto a structure at the back called the retina. Cells in the retina called photoreceptors absorb that light, converting it into an electrical signal that travels to the brain and tells us what we're seeing.

The sun, however, has a lot of light. Focusing all of it onto the retina can cause photoreceptors to absorb high amounts of energy, damaging or killing them.

"Basically, you're killing the photoreceptors from within," said Dimitrios Karamichos, executive director of the North Texas Eye Research Institute at the University of North Texas Health Science Center.

During a total solar eclipse, the moon starts to cover the sun before obscuring it completely. While the sun may appear smaller in the sky, its rays are no less dangerous.

"The sun is still the sun, even if it's partially covered," said Dr. Rafael Ufret-Vincenty, an associate professor in the ophthalmology department at UT Southwestern Medical Center.

It's only safe to look at a total solar eclipse without protection during totality, or the time when the moon fully covers the sun. Timing and duration vary across the D-FW area, but totality is expected to begin in Dallas at 1:40 p.m. and end just under four minutes later.

Symptoms of eye damage

There's some debate about how long a glance at the sun can lead to eye damage. Experts have to rely on anecdotal reports: People come to the doctor with eye damage and guess how long they looked.

Karamichos said permanent damage to the retina can happen in 60 to 100 seconds or less. The retina doesn't have pain receptors, meaning the damage can happen without us feeling it.

People who experience retinal damage after looking at the sun can see a change in their vision anywhere from minutes afterward to overnight, said Karamichos. Symptoms of this condition, called solar retinopathy, include distortion, dark spots in central vision and a loss of sharpness.

There is no treatment for solar retinopathy. The eye could recover on its own—or not. Even if vision improves, some distortion and dark spots may remain. And there's no replacing dead photoreceptors.

"They don't divide, they don't multiply," Ufret-Vincenty said. "So once you lose them, you lose them."

How to view a solar eclipse safely

There are many ways to safely experience a solar eclipse.

Eclipse glasses have a black polymer that blocks out UV rays and nearly all visible light. They typically cost a few dollars. Many online listings for eclipse glasses can be counterfeit, but a list of safe options is available on the American Astronomical Society's website. Glasses should comply with the International Organization for Standardization's safety guidelines. (A note on the back of the glasses should say they meet ISO 12312-2 requirements.) Sunglasses are not protective enough.

At about 12:23 p.m. on April 8 in Dallas, the moon will start to cover the sun. Before totality, viewers will see the sun shrink in the sky until it disappears. They can then take off their glasses and set a timer based on how long totality will be in their area, leaving time to put on their glasses again for the eclipse's final phase.

Can't find eclipse glasses? No problem. Viewers can indirectly observe the eclipse by poking a hole through cardboard or an index card and looking at the shadow cast on the ground when the sunlight filters through. Using a colander, a cracker or even intertwined fingers would produce a similar effect.

2024 The Dallas Morning News. Distributed by Tribune Content Agency, LLC.