Which contrast scheme is best for long hours in front of the computer
screen?

I have used black text on a white background for the past few years for
my programming work.

Recently, I installed a ClearType font from Microsoft specifically
designed to reduce programmers' eye-strain ("Consolas") which had an
incredible effect on my eyes; they are now much less tired after a long
day of work.

However, I still feel there is room for improvement. Any information
highly appreciated.