My problem with this theory is why exactly are Mat's eyes supposed to be the light of the world? He's important, but if anyone should have that title it should be Rand.

If you look at half the light of the world from Mats PoV when thinking about him giving up an eye, it fits.

There's a certain amount of light entering one eye and with both eyes open there's a similar amount entering the other eye.

So you have half the light entering your head, but you still see most of what you did before, not just half.

 

The fact that your eyes are normally focused enough that you don't see double means nothing.

Except that you're not seeing twice as much as you would be with only one eye.

 

My problem with this theory is why exactly are Mat's eyes supposed to be the light of the world?

His world. It was addressed to him, after all.

I see half the light of the world meaning that of the light from the world around him that enters his eyes and is detected by the receptors in his retina, only half will be absorbed and processed now.

 

It is also my thought that Matt will pluck out his own eye before entering the tower to prevent the 'finns seeing what he will do next so he can trick them (when he enters the tower, his memories will be assimilated by the 'finns) and timeframe is irrelevant - if Matt sees it in the future then the 'finns will know it now. Of course, this would rely on the 'finns only seeing through one of his two eyes...