According to an Erich Top Speech, by the end of 1941, the decisive crew fitness requirements were dropped in favor of a more sutiable "Able bodied man" rule.
EDIT: though i would assume - like most military services - eye site must be 20/40 or better without glasses, if the vision is worse, it must be correctable to 20/40 or better with glasses.
not that it really makes a difference now days what the u-boat rules were 65 years ago
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