Sore eyes of our dog

We are wondering with our dog because he had sore eyes for 3 times now within this year. On the first occurrence we were scared because he had difficulty in opening his eyes. It was fortunate that our vet would give us free consultation by phone. After applying the eye drops our dog’s eyes got well on the next day.

After a month the sore eyes recurred. Using the eye drops again it went well after a day. On this last occurrence after 2 months we think there is something wrong. The sore eyes may be caused by a virus so we have to find a way to eradicate it so the ailment will not recur anymore.