Watching a solar eclipse or a partial solar eclipse can be an illuminating experience. But sun watchers must take care. Staring at these amazing astronomical events directly with the naked eye may turn a sunny experience into a visual nightmare. Without proper eye protection, the sun's rays can cause permanent injury, even blindness.
Staring at sunlight, even indirectly — as during an eclipse — can cause a condition known as solar retinopathy. That's a burn to the rear layer of the eye, which can create blind spots in your field of vision. "The damage is at its worst shortly after the exposure," says Don C. Bienfang, M.D., assistant professor of ophthalmology at Brigham and Women's Hospital in Boston.
"There may be some recovery, but there is often a permanent loss of some function," Dr. Bienfang says. "It is very important to emphasize that the area of the retina damaged in solar retinopathy is the most important area of the retina. It is the region of the retina we use when we read."
A solar eclipse occurs when the Earth, its moon and its sun line up together with the moon positioned between the sun and the planet.
A partial eclipse means only part of the sun is covered by the moon. A total eclipse finds the moon covering the entire disk of the sun along a narrow path across the Earth.
Ophthalmologists and optometrists warn that the risk of developing solar retinopathy can't be underestimated and also applies to watching a total solar eclipse.
"No phase of a solar eclipse, even the total eclipse phase, is safe to watch without filters or projection techniques," says Dr. Bienfang.
When you try to gaze directly at the sun with your naked eyes on a typical sunny day, the bright light is so irritating you reflexively blink and close your eyes, says Dr. Bienfang.
During any solar eclipse, the amount of visual sunlight that normally prompts your eyes to close is gradually reduced. So your eye's natural protective reflex isn't triggered. The retinas of the eyes — the fragile light-sensitive lining at the back of each — are left exposed to both visible sunlight and invisible infrared and high-energy ultraviolet solar rays.
"Even in the total phase (of a solar eclipse), damaging radiation is refracting around the black edge of the eclipse and reaching your eyes," Dr. Bienfang says.
When watching a solar eclipse, don't do it looking through rose-colored glasses.
For that matter, never look at the event through optical devices, such as sunglasses, binoculars, telescopes and cameras; smoked or tinted glass; photo film (black and white or color); or developed X-ray film.
A partial or total solar eclipse can be observed safely by: