I think milynor hit it on the head: you're more aware of the water chemistry. What I've learned here is burning eyes tend to indicate high CC and a need to shock. There are other reasons, too. Check out this thread:
http://www.poolforum.com/pf2/showthread.php?t=2987

There might be a simpler explanation: your brother was being polite so that he'd be invited back to swim again!
"...yeah, the pool looks GREAT! Never better! And my eyes don't sting! So...same time tomorrow?"