Bad Astronomy: Misconceptions and Misuses Revealed, from ...

120 SKIES AT NIGHT ARE BIG AND BRIGHT
“The eyes are just barely good enough at rejecting [damaging]
light,” Young told me, because the pupil in the eye constricts dramatically
when exposed to bright light, cutting off the vast majority
of light entering the eye. Most people’s retinae don’t get overexposed
when they glance at the Sun. Young quotes from a paper, “Chorioretinal
Temperature Increases from Solar Observation,” published
in the Bulletin of Mathematical Biophysics (vol. 33 [1971]: 1–17),
in which the authors claim that under normal circumstances, the
constriction of the eye’s pupil prevents too much light from the
Sun from actually damaging the retina. There may be a slight (4 degrees
Celsius) temperature rise in the tissue, but this is most likely
not enough to cause permanent damage.
However, natural variations in the amount of pupil constriction
between different people means that some might still be prone
to retinal damage this way. These people make up the majority of
solar retinopathy patients—people who suffer eye damage from
looking at the Sun.
According to physicians at the Moorsfields Eye Hospital in London,
England, observing the Sun can cause damage to the eye but
not total blindness. On their web site [http://www.moorfields.org.uk/
ef-solret.html], they report that half their patients with eye injury
recover completely, only 10 percent suffer permanent vision loss,
and, most interestingly, never has anyone had a total loss of vision
from solar retinopathy.
So there is damage, and sometimes it can be severe, but most
people recover, and no one has ever become totally blind by looking
at the Sun. However, due to the natural variation in pupil constriction
from person to person, I think I still need to stress that
while it very well may be safe (or at least not very dangerous) to
glance at the Sun, staring at it may still cause damage. The damage
is most likely minimal, but why take chances? Try not to stare at
the Sun, and try to minimize any glances at it. You might be part
of the group that will suffer some injury from it.
So, if the full Sun is not likely to be dangerous, why should
viewing a solar eclipse cause eye injury? During an eclipse most or
all of the Sun is blocked by the Moon. However, think about what
happens inside your eye when you view an eclipse. During a total