Hello, this is Dr. Linda. I hope I can help with your concerns about your rooster, Julius.
From your discription, it sounds as if Julius has picked up a Mycoplasm infection. This is a respiratory infection that can be contracted through the conjunctiva of the eye, hence the swelling. Usually, I will lance the swelling just under the eye, flush throughly with an antibiotic solution, & continue the bird on antibiotics. Since the swelling is still present after 10 days, I would recommend revisiting with your veterinarian to lance or relance the swelling, & submit a sample for culture & sensitivity. This would identify the organism, or confirm it to be Mycoplasma, & also see if a different antibiotic would be appropriate.
Definitely continue to isolate him, & hopefully with additional diagnostics, & another go-round of antibiotics, Julius will be on the mend.
I hope this makes sense & you find the information helpful. Please let me know if you have any further questions or concerns.