Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'm here to help you. I'm sorry to hear that So So apparently has glaucoma in his eye. . .this is what Trusopt seemed to effectively treat. One of the causes of glaucoma is a tumor in the eye. I'm unclear. . . have you continued to use the Trusopt or did SoSo's red eye return after you had stopped the Trusopt?