Eyepatches can help you see in the dark.
Here’s how it works:
You wear an eyepatch over one eye all day whenever you are out in the sun or in a well-lit area. The eyepatch should always be over the same eye whenever you are in the light. Then, whenever it’s dark, switch the eyepatch to the other eye. Your eyes take time to adjust to different light conditions. If one eye is only ever exposed to darkness, and the other one only ever exposed to light, your eyes will never have to adjust. Switching from day-vision to night-vision is as easy as switching your eyepatch to a different eye.
It has been speculated that pirates wore their trademark eyepatches to make it easier to transition from being above deck on a ship to going below deck where it’s darker. Of course, eyepatches have many uses, from covering up injuries, to treating “lazy eye”. For all we know, a lot of pirates could have had lazy eye.