On August 21, millions of people in the U.S. will see the day turn to night as a total solar eclipse sweeps across North America. The last time this happened coast to coast was in 1918. Temperatures will drop rapidly as the moon completely covers the sun. You will be able to see the spectacular colors and light of the sun’s atmosphere, a spectacle revealed to us only during a total solar eclipse.
Although you cannot fully prepare for the sight of a total solar eclipse, ophthalmologists want you to be ready with proper eye protection. Even viewing the smallest sliver of a crescent sun appearing behind the moon is enough to cause irreversible damage to your vision.
Russell N. Van Gelder (photo), MD, Ph.D., clinical spokesperson for the American Academy of Ophthalmology, has treated patients who lost their vision to the sun.
“The total solar eclipse is a wonderful and memorable phenomenon that should be experienced by everyone in the path of the eclipse,” Dr. Van Gelder said. “It is essential, however, that viewing is done safely. Looking directly at the sun, even for brief periods, can cause permanent damage to the retina and result in blindness. I have patients who looked at the sun 40 years ago and still remain without central vision in the affected eyes.
There is an exception to this rule. There is a brief phase during a total solar eclipse when it is safe to look directly at the sun. This phase is called totality, and it lasts about 2 minutes. It occurs when the moon completely blocks the bright face of the sun. But as soon as the sun begins to reappear, put the solar filters back on. The path of totality for the total solar eclipse on August 21, 2017, is about 70 miles wide and extends from Oregon to South Carolina. It passes through Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, 
Georgia, North Carolina, and South Carolina. Outside the path of totality, skywatchers will see a partial solar eclipse.
To ensure that people have the facts, the American Academy of Ophthalmology has teamed up with the American Astronomical Society to offer these five tips:
• Use eclipse glasses and solar viewers specifically designed to block harmful rays from the sun. Regular sunglasses, even dark ones, are not strong enough to protect your eyes.
• Inspect your solar filter before the eclipse and do not use it if it is scratched or damaged.
• Another option is to view the eclipse through #14 welding glass. This is much darker than the visors that arc welders typically use.
• Use solar filters on camera lenses, binoculars, and telescopes.
• Do not use eclipse glasses to look through a camera, binoculars, or telescope. The sun can melt the filter and damage your eyes.