The Reporter-Statesman

Have you ever wondered why pirates are often shown with an eye patch? I've assumed the patch covered a damaged or missing eye, the result of their notoriously violent lives.

But recently a friend offered an another explanation. Perhaps the eye patch had to do with dark adaptation, something close to the hearts of stargazers.

Just as eyes automatically focus when viewing at different distances, they also adjust to the amount of light available. In bright light, our eyes' pupils partially close, allowing in less light, whereas in under low-light, the pupils open wide so more light can enter. In addition to the pupil responses, there are also changes in the retina--the part of the eye that receives the light--that help the eyes adjust.

We're familiar with this. When we walk into a dark movie theater it's often hard to find a seat until our eyes begin to adjust to the darkness. And when we leave, the brighter lights are often uncomfortable until our eyes adjust to the increased light.

Stargazers typically view very faint objects, so we want our eyes as dark adapted as we can get them. Under dark skies, our wide-open pupils and the changes in the retina make it easier to see the faint fuzzies we like to view. However, a second or two of bright light from a flashlight or auto headlight ruins night vision, making it impossible to see faint objects until our eyes readjust to the dark--something that can take several minutes.

Now back to the pirates. On ships where lighting was with candle lanterns, it was rather dark in the lower decks. After being below for a while their eyes would adapt to the low-light and they could see. But if they were to briefly go topside, the bright light would ruin their dark-adapted eyes, making it difficult to see when they went back below.

So, as the story goes, when going topside they covered one eye with a patch so that eye would still be dark adapted when they went back down.

According to my ophthalmologist, Dr. John Quinius, the story could be plausible. Our eyes' pupils normally react in tandem, so an eye patch wouldn't keep the covered eye's pupil opened wide. But changes in the retina occur individually, so the covered eye could conceivably remain more dark adapted.

Of course, if this was common practice, one would think all sailors of the day would have done it, yet I don't recall pictures of non-pirate sailors with eye patches. Whether true or fanciful, it makes for a good--and plausible--story.