Board Thread:Questions and Answers/@comment-5836726-20131016212310/@comment-121.54.44.133-20140125063451

I read an article that Charles' geass is described as 'perfect'. Meaning, he's able to activate and deactivate it at his own will. Unlike Lelouch and Mao, they can't deactivate their geass.

The "DIRECT EYE contact" means his geass won't be working when he can't literally see the eyes. It could possibly mean that, tinted glasses aren't going to work because it literally needs some direct eye contact. Guilford glasses are transparent and Lelouch is able to make a "direct eye contact" which makes the geass work. Every geass have flaws.