run a google search on stereo vision and also depth perception
if I recall, the "floating circle" in a diamond test is kind of a bitch, even with good depth perception
similar to those "puzzles" within a painting, sometimes you stare at it for 10 mins and never get it, others are obvious
here is the company that makes the typical eye-doctor office depth perception test, maybe you can email them technical questions or whatever
http://www.stereooptical.com/stereooptical.com/stereotest main.htm
the FAA 1st class medical has no depth perception tests by the way
FURTHER, I have a few buddies who can only get one or two circles on the above test and these guys play golf, fly big airplanes, and go hunting.
There has been some discussion whether a 20/20 person (corrected with glasses or normal, no glasses) with no other vision problems, and who just cant "pass" the floating circle test, some discussion as to how much weight to actually give the floating circle test.
my .02 cents, I am not a doc