Thursday, August 17, 2017

Safe Eclipse Viewing

Written by  Dr. Eva Hersh, MD

By now, just about everyone in the US knows that a total eclipse of the sun will be visible over 14 states in the early afternoon of Monday, August 21st. Unfortunately, too few people know how to observe the eclipse safely or understand how important it is to protect their vision. And to make matters worse, the market has been flooded with dangerous fake “eclipse glasses.”

People find it hard to believe that a single direct peek at the sun can cause eye damage, but it can. The sun burns the retina because the retina concentrates light. The effect is the same as using a magnifying glass to burn a hole in a sheet of paper. If your roommate or your cousin Bob claims he can stare straight into the sun for five minutes with no loss of vision and says only wusses think they need special glasses to watch an eclipse, please don’t listen because he is wrong. There are no pain sensors in the retina, the part of the eye where images are created. Since people don’t feel pain when the retina is injured, they don’t realize that some of their rods and cones, the building blocks of vision that make up the retina, have been literally coagulated – melted – and permanently destroyed. Because only a small section of the retina is destroyed, there may not be noticeable loss of vision right away. The vision loss becomes obvious as the person ages and becomes blind or near-blind. For an understanding of the importance of doing everything you can to protect your vision, ask anyone blind or with low vision how vision loss has affected their life.

The effect of direct sunlight on rods and cones is similar, but worse, than the effect of looking directly at the bright arc produced by a welding torch or a laser. Anyone familiar with the use of welding or laser tools knows that protective glasses must always be worn to protect the eyes. Speaking of welding, some articles suggest that welding glasses can be used to safely view the eclipse. This is only true if the welding glasses have an infrared (IR) protection level of 14. The IR protection level is printed on the glasses. Most welding glasses are rated at only IR 11 or 12.

For effective eye protection, use NASA or AAS (American Astronomical Society) approved cardboard frame glasses printed with ISO-12312-2 on the frame. Both NASA and AAS have safety information and lists of recommended vendors on their websites. Many of the vendors listed have sold out; you may have better luck starting from the bottom of the list then at the top. Locally, many libraries, science museums, natural history museums, and observatories have glasses available or can suggest where they can be purchased. To protect your eyes, the glasses must block over 90% of all visible and IR light. The lenses should be so dark and block so much light that only the sun can be seen through them. If you put on the glasses (not looking at the sun) and can see anything at all, if you can distinguish a wall from a window or see any edges, the glasses are not dark enough. Check the glasses lenses for wrinkles, scratches, or chips. If any are found, the glasses should not be used because the damaged areas will let in too much light. When you are sure your glasses are dark enough and undamaged, put the glasses on before looking at the sun. Look away from the sun before taking the glasses off.

Some people suggest that children, in particular, should only be allowed to watch solar eclipses on TV. That’s probably going too far. Children should wear the same type of protective glasses that adults do. Children and teens should be supervised to make sure they do not take off their eclipse glasses while looking at the sun. People who wear glasses should put the eclipse glasses on over their regular glasses.

Many ways of viewing a solar eclipse that in the past were thought to be safe are now known to be dangerous. Some examples of protection methods that do not work:

•  Sunglasses, no matter how dark, no matter if prescription or not

•  Smoked glass

•  Any kind of film

•  Polarized filters

Because the lenses in cameras, binoculars, and telescopes concentrate light by thousands-fold, looking at the sun through any of these will cause retinal burns even if you are wearing eclipse glasses. If you plan to look at the eclipse through a camera, binoculars or a telescope, you must attach a filter made for this purpose to the far side of the instrument, not to the side you look into. These filters are available in camera stores.

Eva Hersh is a Baltimore family physician. Send your comments and questions to her by email at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .


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