It might just have heyfever... I would boil some water, add a little salt allow the water to cool down then dip some tissue or cotton wool in the water and gently clean the cats eye lid, you can simulate a sort of licking motion like its mother would have used to clean it, they usually like that.
Trips to the vet are important but I wouldn't put my cats through the stress of it lightly... And really would you go to the docs for a red eye immediately or would you try some home remedies first?