Linda Carroll writes: Anyone who’s walked out of a dark movie theater into bright sunlight knows how painful this can be to the eyes. Imagine how much worse it would be if, like the Chilean miners, you stepped into the light after spending months underground.
That’s why rescue personnel sent dozens of sunglasses into the shaft for miners to wear as they were pulled up to safety. (And not just any sunglasses -- $450 designer sunglasses from Oakley.) For further protection for their sensitive eyes, miners will spend their first few hours in dimly-lit hospital rooms as their eyes slowly adjust to light.
Our eyes have two sets of cells to deal with light and dark conditions, explains Dr. David Sarraf, a clinical associate professor of ophthalmology at the Jules Stein Eye Institute at the University of California, Los Angeles. The six million cone-shaped cells, officially called cones, are what allow us to see what is directly in front of us when the light is bright. These cells also allow us to see color.
The cylindrical-shaped cells, called rods, are responsible for peripheral and night vision. As conditions darken, more and more of our 120 million rods are put to work. But it takes time for the rods to come on line. That’s why you’re almost blind for the first five minutes after you step into a lightless room, and why you can start making out shapes 20 to 30 minutes later.
It’s pretty safe to say that after months in a mine with no light, 100 percent of the rods are on the job, Sarraf explains. And those rods aren’t going to go off line in a flash. That’ll probably take several hours.
With no sunglasses to protect their eyes, the miners would experience significant pain when they hit direct sunlight. “If you jump into brightly-lit conditions with your eyes open you’re going to have stimulation overload,” Sarraf says. “You’re basically releasing a huge electrochemical impulse in one shot. That’s why our instinct is to decrease the light stimulus by squeezing our eyes shut. The pain is a protective mechanism.”