I always found the limit of my fine detail abilities were my hands and not my eyes. The optometrist said I don't "need" glasses, but for reading they might "help" so I never got any. Maybe I just have overly shaky hands, but my biggest problem painting eyes and such has always been shaking and hitting the wrong spot rather than not being able to see the right spot.
I did try a magnifying glass and as others said, need retraining in depth perception so I just gave up after failing at painting a few models