That's at least something to do, checking his eyes and brain to make sure he's not about to implode. The rest is just... weird and a little terrifying, really. All Vash can think of as an explanation is the giant alien.

"That would be great, thank you."

He lets Hilbert direct him in any way he wants so the doctor can look into his eyes... and as soon as a light hits them, they show strange, glowing lines. Almost like circuity, only more... natural. They're otherwise completely normal, healthy eyes. 20/20 vision.