Will looking directly at a solar eclipse make you go blind?
Ever since I was a kid the media have warned about not looking directly at a solar eclipse. The principal at our school would always keep us inside to avoid our burning out our retinas sneaking a peek. Are we all being fooled by an urban legend that keeps getting recirculated every time there's an eclipse? I've never seen a rash of stories after an eclipse about people being blinded or needing glasses because they couldn't resist the temptation to gaze.
We'll get to this directly, but first an acknowledgment. Several times in recent weeks I've thanked Bibliophage of the Straight Dope Science Advisory Board for his aid in preparing these columns, and now must do so yet again. As one of the last generalists in an era of information overload, often I'll find an interesting letter in the Big Box o' Questions and think: Confound it, what did that little man from the Mayo Clinic call eye damage due to eclipse gazing? How gratifying to then find a note from Bibliophage in the margin: Cece, it's solar retinopathy.
Right. To which one can only add that while the danger of looking at solar eclipses may be exaggerated, it's no urban legend. You've never seen a rash of stories about eye damage following an eclipse? Clearly you missed the issues of Documenta Ophthalmologica and other eye journals in which they reported scores of injuries resulting from the solar eclipse visible in Europe, the Middle East, and Asia on August 11, 1999. The number of victims was nonetheless relatively low due to warnings before the event and clouds during, and most recovered fully within a matter of months.
The reality of solar retinopathy having been conceded, plenty of misinformation about the phenomenon has been perpetuated, often by people who should know better. Reviewing pronouncements made before the 1999 eclipse, an editorial in one UK journal observed, "A common characteristic of all these 'expert' views was a virtually complete absence of valid arguments." Among the disputable claims about eclipse watching and sun watching in general:
- Eclipse blindness results from retina burn--i.e., the retina is damaged by heat due to solar radiation passing through the lens of the eye, much as rays focused by a magnifying glass can light a fire. Some authorities feel a more likely explanation is photochemical damage. Were heat the culprit, they argue, eclipse damage would happen quickly, but evidence suggests it accumulates over repeated viewings during the several hours of the event.
- You can go permanently, totally blind staring at the sun during an eclipse. Permanently, maybe. Totally, probably not. An hour of rooting around in the journals turned up no cases of permanent total blindness; even cases of severe initial impairment mostly turned out to be temporary. No guarantees, though--one London eye hospital reported that 10 percent of the eclipse victims they treated suffered some permanent vision loss.
- Glancing at the unoccluded sun for a split second will ruin your eyes. Nonsense. While you may be briefly dazzled, your body's reflexes--rapid contraction of the pupils, averting your eyes--will likely kick in, limiting the danger. For normal unprotected eyes, the damage threshold is in the neighborhood of 30 seconds of direct exposure--still not a long time, I admit.
Miscellaneous facts of interest:
Ophthalmologists can sometimes determine which phases of an eclipse a patient with solar damage was watching by noting the "sickle" on each retina--that is, the arc of retinal swelling that corresponds to crescent-shaped portions of the sun left uncovered at various points.
Whatever may be said about eclipse gazing, you can screw yourself up pretty good staring at the sun while whacked out or in the grip of religious experience. In one report of 300-plus cases of solar retinopathy seen at a clinic in Nepal, 10 percent involved literal sun worshippers--people who gazed at the sun daily or on special occasions. (Some Hindus engage in this practice, often forming a one-hole mask with their hands for the purpose.) Sixties survivors who recall horror stories about people incinerating their foveae while tripping may be interested to know it wasn't just talk--I found a 1976 report of "a 23-year-old man [who] sustained severe macular damage by sun gazing during a hallucinogenic drug-induced state." The hallucinogenic drug was LSD.
Most North Americans have at least a few years to get up to speed on solar eclipse safety. Although those in the southern U.S. and Mexico will be able to catch the edge of the eclipse centered on the South Pacific this April 8, we won't have ringside seats (and then only in western states) till the eclipse of May 20, 2012.