Dont know about this gunnar glasses, but maybe this helps:
Insteed of reading glasses I asked my optician for "office"-glasses. They still forced me to go more near to the monitor then I normaly would do. I then meassured my comfortable distance between eyes and monitor and asked direct for glasses for this distance.
I'm fine now with this solution.
greets
ayla
EDIT: What I maybe should mention:
I'm on computers the whole day long, on work I have to watch very close for down to 2x2Pixel shadows, after work I'm on often for hours, too. Using glasses for the wrong distance made my eyes tired very fast, caused headache and so on. This all is gone now.