( it feels par for the course that natsuno always knows some facet of what she's talking about, which makes him the easiest person to infodump on. so he's actually noticed the symbols, and she's got the insight behind them. )

They're sigils. ( and yanno, she read jade's fonology book and saw some of the sigil work in them, which was large and elaborate and beautiful, and has been occasionally sidetracked in wondering how he got something so complex contained in his iris. high!clarke hadn't thought to ask for specifics. ) He did that to his own eyes when he was a kid, in order to become more powerful. But he messed up applying them, or they were just too rudimentary.

He doesn't need his glasses to see. They just keep his eyes from exploding.