I've been through the Ishihara test a few times but having a go at
http://www.kcl.ac.uk/teares/gktvc/vc...htm#Background
was interesting, since the answers and their 'meanings' are given. I found that on some plates I got the red/green answer, on others I got the 'normal' answer, some I got nothing and on a few I saw part of the normal answer. I guess this means the test is not sensitive enough...as you guys have basically been saying.
Also I notice that at college, when they use green pen on the white board, I struggle to see whats going on...until I put my glasses on ( a really mild prescription..basically the only time I wear them). I have no problem once I have my glasses on.
The point I finally getting to is that when I did fail a lantern test (I was border line) I did not wear glasses at all. I had a prescription from a previous eye test but didn't need glass..didn't get a set.
May be for someone who is borderline...try glasses first! A slightly sharper image might be all you really need.