My Cat's Eyes Are Red, What Should I Do?

We just got back from Scarborough yesterday after a two night stay. Me and my brother rushed upstairs to see my 15-year-old male cat, Tigger. His eyes were sore and so we dabbed them with a cotton ball dipped in hot water, as the vet had previously told us. He's had problems with both his eyes before, so he had eyedrops. The problem went away and only came back yesterday, for all we know. Is their anything we should do?