Teramycin powder -- they call it a puffer -- can be found at feed stores and is a fine powder that is puffed into the eyes. According to label instructions, if you have used it for four days and you see no improvement, then the infection is most likely not bacterial and is possibly viral and you need to see your vet. It is safe for both dogs and cats. My vet recommended it to me because we live on a ranch and the dust blows things into their eyes.
If your cat has a virus such as FHV-1, two very important things to help boost their immune system are l-lysine and L-arginine. The l-arginine is an essential amino acid and is usually found in their food, so check your food label and make sure if you have a cat with a compromised immune system.
As far as dosage goes, everything I have read and been told says the L-lysine is recommended 500mg once or twice daily. Vitamin A is also important to eye health, so a multivitamin is important. It must contain vitamin D to aid the absorption of the Vitamin A.