Swollen red eyes

Hello everyone. Our basset hound Benny recently started getting increasingly droopy red conjunctivitis. Initially our vet prescribed us some antibiotic and steroid eye drops but it didn't really seem to make things better. At first it appeared to get worse when he was outside so we thought it might be allergies. Benadryl does appear to help a little bit. We have also tried eye wash and lubricating eye drops which he hates. It does appear to affect one eye more than another. Our vet mentioned surgical intervention. We just want to do what's best for him. Any advice or experience from others is appreciated.