I buy Royal Canin Feline Health Nutrition Oral Sensitive 30 or Hill's Science Diet Oral Care Adult Cat Food and use it as treats. They like both and it is much cheaper than small bags of treats. They are both large kibble and that is how they clean the teeth. They have to chew.
Have you tried triple antibiotic ointment - Neosporin? I have had great success with it. Around $3 at walmart or any drug store. Just wipe over eye lid.