Things are looking up, but I don't want to jinx myself...
Among the group with the first outbreak everyone looks happy and eyes are healing, 10 days without a relapse now, so maybe we're winning, but can't be sure yet. Crossing my fingers every day!
In the second field were it broke out 10 days ago (when I first posted), I saw the first signs of improvement yesterday (no more miserable sheep, those badly affected look like they have regained some sight). It has gone through everyone now, and no relapses yet but it's too early to tell if it's over... If the second field get over it in 2 weeks without AB jabs that compares rather well to the first field where I gave AB jabs and it took them 5 weeks to get over it, and I still have some badly scrarred eyes.
My problem wasn't that the ABs were not working, they did initially seem to clear up the first signs of infection. My problem was the relapses that followed with aggressive deterioration of the eyes into deep ulceration, which I found very scary - further doses of ABs or Opticlox didn't help at that stage, and the vet had nothing else to suggest.
It's worth noting that the new ram who brought in the infection in the first place got over it in just a few days with as much as a single application of saline eye wash (I didn't have anything else to hand when I first noticed it). He never got severely affected nor did he have a relapse at all despite all sheep around him coming down with it for weeks to follow. Obviously his immune system has dealt with this infection before and was able to fight it quite swiftly and successfully on his own.
So I started thinking that the relapsing problem was down to their immune system not being able to build up a proper response. I can see how a single application of Orbenin or Terramycin or whatever might stop the infection in its tracks IF the animal can quickly mount a proper immune response at the same time and get over it after the first treatment. Unfortunately it seems my animals didn't manage that for whatever reason - only the ram did - even though I've never had any other problems in the whole flock.
So in my case the topical application was more successful as a way of keeping sore eyes comfortable/lubricated and as clean as possible as the body gets on with the healing.
But that's just my sheep and my situation, and my first encounter of pink eye so it took me a while to work out an approach that works for my animals - not without the help of you TAS people
Everyone's sheep and situation is different.