Bizarre. I just put together a quick reader demo last week using blurs to focus the eye (like tilt-shift does for photos).

http://www.swissariknife.com/focus

I added keyboard short-cuts to narrow or widen the number of lines that are 'clear' at a time. You can scroll through while you read or use the arrow keys.

I ended up just hard-coding it using HTML spans and text-shadows to demonstrate the effect. This is NOT an actual solution, just an experiment.

Warning: This may appear way differently in different browsers and possibly not at all. The effect generally works in FF/Safari/Chrome.