Permanent eye damage can occur in as little as a minute and a half from looking at the disk of the Sun directly, or through a camera viewfinder, or with binoculars or a telescope even when only a thin crescent of the Sun or Baily's Beads remain during a solar eclipse.

In one study when people who stared directly at the sun for several minutes during the 1999 eclipse went to see their doctor, about half had permanent damage.

The moment you begin looking at the sun, you start to develop a sunburn on your cornea (eyeball), known as photokeratitis. The cells of the cornea, the transparent outer layer of the eye, will blister and crack when overexposed to UV light.
Symptoms of this condition are pain that feels like you have dirt in your eye, tearing excessively, redness and an extreme sensitivity to light. They usually appear a few hours after the damage has occurred. Exposure for short periods will usually dissipate within 36 hours. (Gizmodo.com)

Most of the damage is caused by ultraviolet (UV) light. During sunsets, when the intensity of ultraviolet light is lower due to scattering you can look at the sun, but avoid looking directly at it for more than a few minutes at a time.

Looking at the sun steadily during midday for longer periods can cause damage to the retina, the collection of light-sensitive cells located at the back of the eye. Solar retinopathy, as the damage is known, may not be painful like photokeratitis--but the results can be permanent. It is like macular degeneration, resulting in blindness in the center of your field of vision. Basically, that black dot you see after a photo flash that would just never go away.
It will sometimes go away within a year, but if it hasn't gone away by 18 months it is likely permanent according to a report in the journal "Graefe's Archive for Clinical and Experimental Ophthalmology."

Viewing a total eclipse:
See 2017 eclipse

There are several ways to observe an eclipse safely;
Special glasses that meet the ISO 12312-2 safety standard. See below.
Welder's goggles with a rating of 12-14. 12 may be too bright, 14 too dim, but 13 is hard to find. (Warning: Harbor freight flip up welder goggles are only #10).
In the old days we used to look thru 2 pieces of overexposed camera film negative or make a pinhole camera.

During the short time when the moon completely obscures the sun - known as the period of totality - it is safe to look directly at the star, but it's crucial that you know when to take off and put back on your solar glasses.

Look for crescent shaped images of the eclipsed sun in the shadows below a tree. The leaves create the effect of a pinhole camera.

See Reputable Vendors of Solar Filters & Viewers | American Astronomical Society (AAS)
Paper ISO certified glasses (block out 100% of harmful UV and infrared as well as 99.999% of intense visible light) and can be found for as low as $1.00.
Note: Many were sold out 10 days or more before the eclipse.

Paper ISO 12312-2 certified glasses (block out 100% of harmful UV and infrared as well as 99.999% of intense visible light) can be found for $1.00 *.
Most are paper with silver coated mylar or scratch resistant optical density 5, "Black Polymer" lenses.
* On Friday 3 days before the eclipse, most places were sold out.
Some were selling 5 or 10 packs for $50 - $100 but wouldn't guarantee delivery by Monday.
You can put them under or over prescription lenses.
They can also be used for viewing sun spots or planet's transit across the sun.

Links:
Observing Solar Eclipses Safely | mreclipse.com
Solar eclipse 2017: Simple, safe ways to see the moon block the sun - Business Insider
Listen to the NPR report on eye protection with Ralph Chou, professor emeritus of optometry and vision science at the University of Waterloo, who's a leading authority on eye damage from eclipse viewing.

How long does it take before your eyes get damaged when looking at the sun? | UCSB Science Line
NASA Eye Safety During Solar Eclipses and Eye Safety During a Total Solar Eclipse
What Happens When You stare at The-Sun | Gizmodo.com
Listen to the NPR report on eye protection with Ralph Chou, professor emeritus of optometry and vision science at the University of Waterloo, who's a leading authority on eye damage from eclipse viewing.
How long do you need to look at the sun to damage your eyes? - Quora


Return to The eye or the 2017 eclipse

last updated 14 Aug 2017