Do you know why in the days of wooden ships and powder monkeys, sailors wore an eye patch? Because the black powder was stored in a powder magazine deep in the ship. The magazine was illuminated by a special lamp with triple pains of glass to prevent sparks but it was extremely dim. If a Powder Monkey went below deck to the magazine after being in extremely bright sun he would be blind. Think being hit with light directly from the sun, reflecting from the sails and water. Then walking into a room lit with less than birthday candle. They wore one eyepatch to shield one eye from the sun. Once below deck they flipped the patch up to see in the dark.