Blind Equals Bad

This is actually an idea my brother came up with.
We play D&D, so this is really a possible scenario (especially considering the group we play with...)

Anyways, for those not familiar with D&D, when a cleric casts the spell Detect Evil, he gets a sense for how evil nearby creatures and objects are.
If a creature of unspeakable evil is nearby, said cleric will go blind.

I hope you can figure out the rest.
Enjoy.