Is the eye draining? If so, is the drainage clear, likes tears, or does it have a color to it. Does the other look completely normal? I am not famliar with Terramycin. Sounds like a standard antibiotic to me. I would do a search for the colloidal silver on BYC. maybe somebody with much more experience treating sick chickens can give advice on dosing. ( I'm an RN so my advice is based on what I would do if the hen were human. Infection is infection, inflammation is inflammation.. you know what I mean?) I would suggest the Vetricyn eye wash. Any decent pet store will carry it. It will flush out the eye, sooth it and is antibacterial.