Eh, well, my reasoning was that since the majority of the crew might've spent most of their time inside the sub, then good eyesight might not have been the biggest issue for them. If you've ever been in a WWII sub, you'll know that there isn't exactly a lot of space to stretch your eyes.
But then, I'm assuming that certain crewmembers were assigned as lookouts, as opposed to the entire crew taking turns. Does anyone know how that worked?
Also I might be a little biased, as I'm nearsighted myself
You all make good points on the subject, and I can definitely see why good vision would be a requirement.