On Monday darkness will sheath large swathes of the country in the first total eclipse to completely cross the continental U.S. since June 1918. The eclipse will first be visible in Oregon just after 10:15am and will travel in a south-easterly direction ending at the South Carolina coast at roughly 2:45pm.

During an eclipse the moon passes between the Earth and the sun. Due to the Earth’s close proximity to the moon it appears to block out the sun’s light for those at certain alignments. Eclipses actually occur quite often, however these are mostly partial solar eclipses due to lunar distance from Earth.

A common public misconception is that the sun can be safely viewed during an eclipse. However the moon passes the sun so quickly (at 2880km/h) which means most of the time individuals (even those in the direct path of totality) will be experiencing a partial eclipse, and will be exposed to the sun’s core. The macula, the center part of the retina, can be permanently damaged in a few seconds of viewing.

“Confusion between viewing the corona vs the sun’s core is increasingly likely during the brief transition from partial to total eclipse and then back to partial eclipse,” write researchers from The Vanderbilt Eye Institute, TN, in a Viewpoint published in JAMA Ophthalmology. Retina damage during an eclipse can occur in two ways: through near-infrared radiation (700–1500nm) causing direct thermal injury and, more likely, through excess visible light which can cause photochemical toxicity through “rapid accumulation of reactive oxygen species and free radicals.” 

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Studies examining post-eclipse clinic visits have confirmed that photochemical toxicity is the more frequent cause of damage in solar retinopathy (Wong, SC et al. 2001), which includes retinal pigment epithelium and photoreceptor atrophy in the fovea. Ophthalmologists should consider solar retinopathy in patients with unexplained visual loss symptoms after the eclipse, say the authors.

There are a number of ways to view the stunning spectacle. These are detailed in a safety notice published in JAMA and include:

  • Viewing through no. 14 welder’s glasses
  • Viewing through undamaged aluminized Mylar filters
  • Viewing through glasses that meet the International Organization for Standardization 12312-2 standard for protection
  • Using a pinhole projector (with your back to the sun and only looking at the image on the paper)

The authors warn that it is not safe to use any of the following to look at a solar eclipse:

  • Unfiltered binoculars or telescopes
  • Regular sunglasses
  • Cell phone cameras

For more information visit JAMAnetwork.com.