[PeterM]

I saw a well known amateur many years ago at Astrofest wearing dark sunnies and a beanie he would pull over his head when venturing outside during the day, a friend assisted him to get around. He is one of the finest visual observers in Australia and from what he said it definitely gave him the edge while looking for very faint objects. I think - from an amateur astronomers needs,the eyepatch is less about preserving night vision and more about comfort at the eyepiece as many strain to keep one eye closed while viewing through the scope with the other as we are so used to having both eyes to view - it comes naturally with practice. As far as keeping stray light out of your other eye perhaps, but practice soon makes the patch redundant. There are very deep red goggles available from Orion delaers that help if you want to go into the kitchen at night to get a cuppa. They may even help you during the day to maintain that little extra dark adaption at night - they are about $40. I have often wondered if these goggles took off in a big way what visitiors might think of a field full of red bug eyed people wandering around the observing field - a weird mob perhaps. The cheapest and generally most effective way has always been a sheet of dark cloth/material over your head.
PeterM