Yeah, I'm not sure you can say anything meaningful about eye strain and readability without accounting for room lighting, glare, and other reflective surfaces and distractions. If I'm in a dark room with a bright screen, it's almost physically painful to stare at the screen. I have to turn the brightness way down, and then I lose contrast and have to strain even more. In an office with horrible flourescent lighting, highly-reflective white walls and surfaces, metallic accents reflecting light into my peripheral vision, reflective monitors (Apple displays are the worst), and eyeglasses, I'm practically blinded. The last thing I want is glaring white light from my application windows.
There are things other than black-on-white and the inverse. I've been using Solarized dark where possible for years, especially in code windows. White-on-black is horrible, but pastel colors on a slate blue-gray background is the most comfortable option for me.
If you're using a monitor with separate brightness and contrast settings, you might also choose to lower the contrast a bit. When my monitor's contrast is at 75%, white doesn't really get less bright until somewhere around 30% brightness. But I'd I lower contrast to 50%, then 50% brightness makes a bigger difference, without losing readability.
There are things other than black-on-white and the inverse. I've been using Solarized dark where possible for years, especially in code windows. White-on-black is horrible, but pastel colors on a slate blue-gray background is the most comfortable option for me.