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Posted on 08-07-2017

“and the sun had appeared to be fighting with the moon…”[1]

Today, we are inundated with instant news. Through our phones or online, world events seem to spread to us in only a matter of a few seconds. We can anticipate and prepare for events like the upcoming solar eclipse through news from astronomers, who have calculated when eclipses will occur for roughly the next millennia-a convenience for those wishing to view the event safely without damaging their vision.[2]  In ancient times, solar eclipses weren’t so easily predicted. First-hand accounts depicted on clay tablets[3] and stories of celestial gods battling for dominion over the sky[4] are some of the first sources of solar eclipses, which likely did not pass to ancient people though their Twitter feed. These accounts, however, serve as some of the earliest explorations into the study of how our eyes are affected by the sun’s powerful light.[5]

Can a solar eclipse really damage my vision?

Solar retinopathy is a diagnosis applied to those individuals who experience central vision loss during or after prolonged high intensity exposure to light energy, most commonly sustained during solar eclipse events.[6] Researchers believe that this occurs due to solar radiation damage to rod cells of the parafovea retinal tissue.[7] A plethora of case studies have been conducted on individuals to measure the effects of exposure to the sun, both during solar eclipse, and while viewing a fully-exposed sun. Although risk associated with solar retinopathy is quite low (only 1 in 100,000 solar eclipse viewers[8]) there is no clinical treatment for those who have suffered a solar injury, making the prognosis for recovery unpredictable. In a 1976 solar eclipse in Turkey, 58 patients (86 eyes) were observed with solar retinopathy symptoms and their prognosis tracked for 18 months.[9] Only about half of patients who experienced visual acuity damage during the eclipse event regained their pre-eclipse vision; most recovery occurring during the first two months of the 18-month case study.[10] In other accounts, like in the case of the 1991 eclipse in Mexico, 21 patients with diagnosed solar retinopathy were fully recovered after only four months.[11]

The risk associated with solar eclipses may lie in the reaction of the eye to the sun’s disappearance behind the moon. In normal outdoor conditions, when the sun is at its zenith, our eyes react by constricting the pupils to allow less light intensity to enter the eyes. Inversely, in eclipse conditions, the low level of illumination allows the pupil to open up, allowing more light to enter through the iris and onto the retina.[12] Prolonged solar radiation, which can occur when one stares at the sun as it enters total eclipse, causes rod cells located in the retina to generate free radicals that damage the eye, and ultimately affect visual acuity.[13]

Certain ocular factors can cause individuals to be more at risk for solar retinopathy[14]:

  • Younger individuals (0-20 years of age)[15]
  • Clear interocular lens
  • Dilation drugs, or stimulants

So, to answer the question that has had moms everywhere warning us to not stare at the sun; yes. Yes, the sun’s light energy can damage your eyes during a solar eclipse. But, that doesn’t mean you can’t take measures to protect your eyesight while still catching the event.

The Do’s and the Don’ts

Unlike your average sunny day on the lake, a solar eclipse requires more than your favorite pair of sunglasses for safe viewing.

Do’s:

  • Wear eclipse glasses: These glasses are made of materials that block out 99.9% of the sun’s harmful light
  • Use telescope solar filters: When fitted properly over the objective/front end of a telescope, they offer a fantastic and safe view of the solar eclipse
  • Find Welder’s Glass #14: Not every welder’s glass will work, but Number 14 gives optimum protection for which to view the eclipse
  • Make a pinhole viewing box: Simple instructions can create a safe and effective method of watching the eclipse.

Don’ts:

  • Wear sunglasses: Sunglasses will NOT offer enough protection to block the sun’s light energy for the extended amount of time that the eclipse will be viewed.
  • Use mylar balloons: It might seem like a great idea at the time, but balloons are useless for blocking any amount of light energy
  • Use smoked glass: the only glass which will work effectively is Welder’s #14.
  • Use binoculars, unfiltered telescopes, or magnifying glasses
  • Use coffee or tea bag filters: just don’t do it.

In 20 B.C.E. China, Liu Hsiang describes that, “when the Sun is eclipsed, it is because the Moon hides him as she moves on her way.”[16] As you move about your day on August 21st, take the precautions to “hide” your eyes with safe solar viewing tools, so that you can be part of the next thousand years of eclipse storytelling.

-CTCG


[1] Livius, Titus. The History of Rome, XXII, 1, 4:8.

[2] Espenak, Fred and Meeus, Jean. “Five Millennium Canon of Solar Eclipses: -1999 to +3000,” NASA Technical Publication TP-2006-214141: 2011. https://eclipse.gsfc.nasa.gov/SEpubs/5MCSE.html

[3] T. de Jong and W. H. van Soldt. “The earliest known solar eclipse record redated,” Nature Vol. 338: 1989.

[4] Livius, Titus.

[5] Splinter, Robert and Hooper, Brett. “An Introduction to Biomedical Optics,” Taylor & Francis Group: 2007. Pp. 4-6.

[6] “Solar Retinopathy,” American Academy of Ophthalmology: 2016. http://eyewiki.aao.org/Solar_Retinopathy

[7] Hope-Ross, M.W., et al. “Ultrastructural Findings in Solar Retinopathy,” https://www.nature.com/eye/journal/v7/n1/pdf/eye19937a.pdf 

[8] Young, Andrew T. “Galileo, Solar Observing, and Eye Safety,” 2015. http://aty.sdsu.edu/vision/Galileo.html

[9] Atmaca, L.S., et al. “Early and Late Visual Prognosis in Solar Retinopathy,” Arch Clin Exp Ophthalmol Vol. 233: 1995.

[10] Atmaca, L.S.

[11] Juan-López, M. and Peña-Corona, M.P. “Estrategia para prevenir daños a la salud ocasionados por la observación del eclipse solar en México,” Salud Pública de México Vol. 35:1993. Pp 494-499

[12] Young, Andrew T.

[13] Hope-Ross, M.W. et al

[14] “Solar Retinopathy”

[15] Two separate case studies were conducted (See: Istock, “Solar retinopathy: A review of the literature and case report” Journal of the American Optometric Association 56:1985. Pp. 374-382 and Rothkoff, et al. “Solar retinopathy: Visual prognosis in 20 cases,” Israel J. Med. Sci. 14:1978. Pp. 238-243) which resulted in an average diagnosis age of 20 years of age or younger.

[16] Cit. in Khai-Yuan Chan Ching, Ch. 9, Pp. 3a.

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