University of California, San Francisco, UCSF Medical Center
Learn helpful tips to protect your eyes when viewing a total solar eclipse.
A solar eclipse was visible across the United States on Monday, August 21, 2017 the first coast-to-coast solar eclipse in 99 years! The next total solar eclipse visible from North America will be April 8, 2024.
A total solar eclipse occurs when the moon completely blocks the sun from our view. While this event is sure to be awe-inspiring, it is extremely important to ensure you are viewing the eclipse with the appropriate safety measures in place.
Unless you are in the “path of totality,” which occrus when the moon completely covers the Sun's disk, it is not safe for you to look at the sun with the naked eye at any time. This is because you will be viewing a partial solar eclipse, and even if only a small sliver of the sun is visible, you can cause permanent and irreversible damage to your retina by looking directly at the eclipse. With a partial eclipse, there is a crescent-shaped blind spot, instead of the large central blind spot of the total eclipse.
Solar retinopathy (retinal damage that results from exposure to the sun’s radiation), occurs after sungazing. Risk factors include young age, having a clear lens (either because you are young and don’t yet have a cataract, or you have already had cataract surgery), large pupil size, and certain photosensitizing medications (such as tetracycline, which is a commonly used antibiotic).
You may also be eager to teach your children or grandchildren about the solar eclipse, and therefore it is even more important to understand safe eclipse viewing practices and to discuss these important steps in advance. Even quick glimpses with the naked eye are not recommended, as damage to the delicate light-sensing tissue, the retina, can still occur. This is because the light-sensing cells of the retina are very sensitive to light, and it only takes a few seconds for damage to occur.
To safely view the eclipse, you will need special eclipse viewing glasses or solar filters. You cannot use super dark sunglasses or make your own filters using dark glass or silvery wrappers. Do not look at the sun through a regular camera, telescope, or binoculars (indeed, you should not do this even while wearing solar filters, as these optical devices may concentrate the damaging solar rays and enter your eyes).
The only way to ensure that the solar filters you have purchased indeed meet a specific worldwide standard known as ISO 12312-2 is to check the American Astronomical Society’s “Reputable Vendors of Solar Filters and Viewers” page. If you are purchasing online, you can cross check that the vendor is on this list.
Be sure to also review the safety pages at NASA and the American Academy of Ophthalmology. NASA also has an excellent FAQ page.
To summarize: A total solar eclipse is safe to look at directly with the naked eye only if you are in the “path of totality” and the moon completely blocks the sun. This lasts for a few minutes, and it is only during this time that one can look directly at the eclipse. If you are one of the lucky ones to view a total eclipse, enjoy this most wondrous spectacle! The rest of us under a partial solar eclipse will use reputable solar filters for viewing. For everyone, stay safe!
Yvonne Ou, MD, is a board certified ophthalmologist who specializes in glaucoma, including medical, laser and surgical therapies; cataract evaluation and treatment including combined cataract and glaucoma surgery; glaucoma filtering and implant surgery; and newer procedures.
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