Quick: list essential parts of a pirate costume. How many items did it take before you arrived at eye patch? Not many, right? To my surprise, there may be more value to that eye patch than, well, meets the eye. ITS Tactical, in an article on preserving your night vision explains:
Now we come to the most historically debated method of retaining your night vision, eye patches. I say “most debated” because of the lore surrounding Pirates using Eye Patches to aid them in adjusting to darkness when moving below the deck of a ship. There was typically no light below deck other than ambient light and these sailors would need to quickly adjust during battle, etc.
As a retired submarine officer, I can tell you the eye patch solution works but, with a minor loss of depth perception because you are looking through only one eye (need two eyes for good depth perception). In many submarine movies you see officers at night wearing red lens glasses or goggles. While, promoting night vision, red lenses have a short coming. Anything in red cannot be seen, since the red wave lengths blank out anything in red. This means that you cannot see out of specification readings which are written and circled in red, your red soundings and other critical features on charts cannot be seen, and you cannot differentiate wires, leads, valves, or signs in red, unless you remove the red goggles or glasses-- which when removed ruins your night vision. Since submarine OODs have to night vision adapted between nautical sunset and nautical sunrise I wore an eye patch. This allowed me to see everything in normal light-- including items in red--while maintaining night vision in the other eye. If the sub had to come Periscope Depth (PD) you could maintain your night vision in the patch covered eye until the control room was rigged for black and you were ready to put that single eye to the raised periscope eye piece. You see when " dancing with mother Kollmorgen" you only need to use one night adapted eye.
For non-boat sailors: mother Kollmorgen is another name for the periscope which was manufactured by Kollmorgen. Dancing with Kollmorgen is based on how sometimes you looked with your arms around the periscope manipulating it--it sort of looked like how you would your mother or grandmother if you were dancing with them in public.
Not a bad for a $3.00, indestructible hack.