Why do pirates wear eye patches? That was the topic of conversation at the dinner table a week or so ago. There is an assumption that pirates wear eye patches, all pirate fancy dress comes with a black eye patch, but photographic evidence showed that Johnny Depp didn’t wear one, and nor did Captain Hook. The task in hand became to search out the evidence. Do pirates actually wear eye patches, and if so, why?

It’s without question that piracy is a dangerous way of life. Not only is there the seasickness to contend with, there is much fighting and looting along the way. It is very likely that a pirate could lose an eye to injury, either directly or due to a subsequent infection, and with prosthetic eyes in short supply on the High Seas, covering up the damaged eye or empty eye socket would be a quick fix to a long term problem. It is doubtful that the pirate would worry much about the cosmetic effect, and even less likely he would think about infection control. But did pirates actually wear eye patches? The more I searched, the more the pirates appeared patchless. Except Long John Silver in Treasure Island. Trawling the Internet, speculation about pirates and eye patches was rife. Yes they did, no they didn’t, lots of good theories but no hard evidence – except from the American film industry.

So here is the best of the scientific theory, completely unsubstantiated, open to criticism, but widely quoted as being true. Pirates survived by stealth and robbery. In order to take a ship, or even a port, they needed to be able to fight accurately and have an element of surprise. Pirates needed excellent vision. The theory of the eye patch suggests that one eye be exposed to light and the other be covered and so used to darkness. The eye requires a certain light intensity for optimum vision, and so the pupil reflex acts to control the iris, the muscular diaphragm around the pupil (the hole where the light enters). In bright light, the pupil is small so less light reaches the retina than in dim light when the pupil is large. Could the patch be used to allow for one eye to be adjusted for bright light (on deck or on shore) and the other be adjusted for lower light intensities (below deck or in caves and cellars). Could the pirate swap his eye patch from eye to eye depending on the light intensity of his surroundings. It’s plausible, and has come to be a widely held belief. But, there is no actual evidence for it. If we consider how the human eye works a little further, we can also reason why this may not be the case at all. Humans have binocular vision. Both eyes point forwards and each eye “sees” a fractionally different image of the same object. The brain puts these two images together and the perceived image is a three dimensional picture that allows distance to be judged. Animals that hunt, the primates and the predators, need to be able to assess distance when chasing their prey. If a pirate were to cover one eye, he would no longer have stereoscopic vision and would find it much harder to judge distances between two objects. Not a skill that a pirate would want to abandon when fighting an opponent with a sword or a cutlass.

Am I any the wiser in understanding why a pirate would wear an eye patch? Not at all, in fact I’m not even sure that traditionally they ever did. I couldn’t find much evidence to support the claim. What I have been able to do is look at the theory and critcally examine that theory in line with the available scientific fact.