There's no alternative to catching him and having a look. In this dry dusty weather he may simply have got some coarse dust in which is irritating the eyes.
It could be that he has entropion where the eyelashes are turned in and scrape on the eyeballs - although I would have thought that would appear younger - but I've not seen it so I don't really know.
For anything eyeball I use Orbenin ointment from the vet. It's worth always having a tube to hand. It heals many eye problems.
There are other possibilities but these are the two I would look for first.