Never heard this. Had night lights throughout our homes as kids, never any issues with sight. Still have 20/20 vision and good night vision (at 45 years young). Never needed glasses. Not sure what kind of night lights my mom and dad (and grandparents) used in the 60s and 70s, but they were typically very soft light and hidden behind something decorative, giving just enough light to tell us "There's the bathroom," or "There's the door." :-) Where did you hear of this information? Generalizing night lights as causing some type of blindness, without specifying what kind, what brightness, whether there was any disposition to night blindness in the first place, etc., sounds a bit like speculation, but again, I'm not sure. Maybe the Doc would know. :)
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I also cosleep with my daughter in total darkness.  She has no need for a nightlight and has no fear of the dark whatsoever.   She is not even three yet and can also manage to work her way out of the room when she wakes up.  I believe it has enhanced her confidence levels.
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