Newswise — ANN ARBOR, Mich. -- On Monday, Aug. 21, a total solar eclipse will offer a rare — although brief — sight to millions when the sun disappears fully behind the moon. An otherwise bright summer sky will give way to total darkness.  

Is it OK to have a peek?

The answer: not without the right protection.

“It’s unsafe to look at the sun with your naked eye — or with conventional sunglasses, a smartphone, binoculars or a telescope,” says Rajesh Rao, M.D., a retina surgeon and an assistant professor of ophthalmology and visual sciences at the University of Michigan Kellogg Eye Center.

That’s because staring at the sun, no matter how small the sliver or length of time, can cause temporary (and sometimes permanent) vision damage.

“As doctors and ophthalmologists, we want to make sure everyone is taking proper precautions,” Rao says. “We know there’s a lot of excitement. People want to look.”

Such events, after all, occur once every 18 months, but this eclipse — to take place Aug. 21 — marks the first time in nearly a century that the eclipse will stretch across the continental United States.

Ordinary sunglasses and camera or telescope lenses don’t protect your eyes. Use specially designed glasses, viewers and lens filters to block the sun’s harmful rays instead.

Glasses for solar eclipse protection

Fortunately, you can watch an eclipse through specially designed glasses with solar filters.

Viewers, Rao says, should only purchase ones with an “ISO 12312-2” designation that indicate the product has met international safety standards (the American Astronomical Society has a list of approved brands). Discard any approved solar filters that have scratched surfaces and get a new pair.

When to wear these solar filters depends on the phase of the eclipse, Rao says.

A moment called totality is the period when the sun’s face is covered entirely by the moon and the sky is the darkest: the so-called “total eclipse.” Before and after the total eclipse, the moon blocks only part of the sun’s phase, a period called “partial eclipse.”

When it’s evident the partial eclipse has started, look away from the sun and put on the solar filters. Once the filters are on, you can look back at the partial eclipse.

Only during totality or total eclipse — which lasts less than three minutes — can the special glasses with solar filters be removed.

“The moment it becomes a partial eclipse again, you have to put them on again,” Rao says.

Many, though, won’t be able to catch an unprotected glimpse.

The total solar eclipse only will occur on a 70-mile-wide path stretching from Oregon to South Carolina. Everywhere else in the country (Michigan included) will see only a partial eclipse.

In those places, there’s no safe time to remove the protective eyewear.

Why you should protect your eyes from the sun

Our eyes are conditioned only to handle typical daylight conditions.

“The cells in the retina, the back part of the eye, are accustomed to light levels that are more consistent with our ambient light levels,” Rao says. “Being indoors, for example, or going outside but not looking directly at the sun.”

Looking directly at the sun without proper solar filters can quickly spell trouble.

Specific wavelengths of light within the sun’s powerful rays can damage retina cells — namely, those in the fovea, a tiny pit in the central retina that facilitates high-acuity vision for reading, facial recognition and driving.

That damage can cause a partial retinal “hole” to develop, or other changes, in a condition called solar retinopathy. Depending on the length and extent of exposure, outcomes may vary. Blurred vision or seeing spots could be temporary.

In other cases, the injury is permanent; eyesight won’t return to normal.

Although most people know they shouldn’t look directly at the sun, Rao understands that the forthcoming solar eclipse is a rare event that will draw many eyes skyward.

“Our main goal is that you enjoy this once- or twice-in-a-lifetime opportunity while protecting your eyes from a substantial chance of vision loss or blindness,” he says.