Aug 16 2017
While millions of people are looking forward to witnessing celestial history when the first total solar eclipse visible in Illinois since 1889 takes place on Aug. 21, Kirk Packo, MD, is worried about medical history repeating itself.
"The first big description of sun damage to the eye occurred following a total solar eclipse that went through Europe in 1912," two decades after the first instrument for inspecting the eye was invented, says Packo, the chairperson of the Rush Department of Ophthalmology. "People are excited to view this historical event -; myself included. But history tells us that if they are not prepared, they can do lasting damage to their eyes."
Eclipse's 70 mile-wide shadow will pass from Portland to Charleston
On the 21st, the moon will pass between the earth and the sun, casting a 70 mile wide shadow that will pass across the country from Portland, Oregon, to Charleston, South Carolina between roughly 9 a.m. and noon Chicago time. While partial solar eclipses occur regularly, this event will be the first total solar eclipse visible from the contiguous United States since 1979, and the first visible in Illinois since a century before that.
Huge crowds are expected to gather in that 70 mile wide shadow – known as the zone of totality – where the sun will be completely obscured for a few minutes except for a ring of fiery light. The destinations include downstate Carbondale, Illinois, near the center of the totality's path, where the eclipse will be visible from 11:52 a.m. to 2:47 p.m.
Eclipse removes pain of looking at the sun, but not the harm
Only people watching the eclipse in the zone of totality will be able to look directly at the eclipse, and then only for the few minutes when the moon has completely covered the sun, without hurting their eyes. Packo cautioned that anyone viewing the eclipse anywhere outside the zone of totality (which accounts for most of the country, including Chicago) needs to avoid looking directly at it without eye protection at all times.
The darkened skies allow people to look at the obscured sun without the normal physiological reaction to close their eyes, just as if they were looking at a similarly bright full moon. Nonetheless, Packo says, dangerous ultraviolet light is still entering the eye and damaging the retina, the collection of light-sensitive cells located at the back of the eye that transmits images to the brain.
"When you are looking at the eclipse, you are not getting the painful stimulus, because most visible light has been darkened. Yet all that time, you are letting the invisible, dangerous light energy through." Packo explains.
"Since there is no feeling to the retina, people don't even realize that they are developing tiny, pinpoint, burns in the retina." These retinal burns can cause lifelong dead spots in the center of a person's vision.
Pinhole cameras, NASA-certified glasses allow for safe watching
Packo stresses that there are only two ways to safely view the eclipse: Indirectly by creating a pinhole camera, or by wearing special glasses with lenses rated to block the full spectrum of light. While dozens of these eclipse glasses are being advertised, Packo recommends visiting the NASA website, which lists which of these brands of glasses have been certified as safe.
Beyond people buying unapproved glasses, he is concerned that eclipse watchers will simply wear multiple pairs of UV-blocking sunglasses. This approach "could lead to more damage, because things will look darker, so you may stare longer, but the invisible thermal-damaging light is still coming through."
Packo also warned of yet another dangerous practice even when using the approved solar eclipse glasses. "These glasses are designed to wear and to look at the sun without magnification in front of the glasses. If an observer uses binoculars or a telephoto lens on a through-the-lens camera viewfinder, the now highly focused sunlight energy can damage the solar glasses allowing through dangerous light levels." He added that the proper way to view the eclipse with magnification is to obtain an approved lens to attach in front of the binoculars or camera lens, not simply over the observer's eye. "All this takes planning."
Packo won't be traveling to Southern Illinois to view the eclipse from the zone of totality, but will be safely watching the near totally eclipse safely from Chicago through the right lenses. He wants to remind others that not being prepared could mean that the lifetime memory of the upcoming eclipse could be lifelong dead spots in the center of their vision. He added, "Remember that if you are making these decisions for your children too as you watch this exciting event together, make sure you give them the right memories too."
Source: https://www.rush.edu/news
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