Thank you Denzil,
First, I have to say that I am quite concerned about the extent and severity of Trevor's signs. Now just to shed some light on what you are seeing, the ocular signs are advanced and indirect signs of the dropsy. His eye is essentially bulging because the fluid build up in the body is pushing against it. This is sometimes referred to as Pop-eye.
As well, as the eye is being forced forward; which will cause increased pressure behind the eye as well as making it more prone to external damage by being displaced. With these two factors, we often see the other signs you have noted, corneal edema. The cornea is the clear protective cover over all our eyes, when it is inflamed, traumatized, or irritated; this tissue will become cloudy or hazy (since it cannot swell like a traumatized finger or toe would). It is a sign that the pop-eye is compromising the eye’s health. And often if we cannot address the root of the cause (or if there is damage to the cornea externally), we will lose the eye.
Next, we have to consider those black lesions on his skin. In this case, we can see discoloration of this nature associated with ammonia burns but also can see septic lesions in later state dropsy cases. Now you noted the ammonia as checked but not when. If it was before the treatment, I’d be concerned that it is no longer within range. The reason is because we can see ammonia levels skyrocket when we use these treatments in our tanks (hence why we need to keep a close eye and keep the water perfect when using medications). If the ammonia is high, then it is likely the trigger for the skin lesions. If it is currently within normal range, then it is likely that these discoloured lesions are secondary to sepsis (bacteria in the bloodstream).
Finally, we need to discuss Trevor’s lack of treatment response. Now as I am sure you are aware dropsy is a disease that can be induced by a few different disease processes. Bacteria infection is commonly assumed and what people treat for (because it is the most treatable). That said, it is not the only cause and at his age we do need to think about other dropsy differentials that wouldn’t have responded to this treatment, kidney disease and failure. Because at his age, this could very much be the reason for his signs and why he didn't respond to your treatment (and perhaps worsened with it).
Furthermore, unless we are ultrasounding or x-raying our poorly fish, we cannot assume that this distension is due to fluid at all. In fact, we can see a similar presentation with or we may be seeing an intra-abdominal tumor (these are often linked to the reproductive organs). So, his lack of response does raise some serious concerns not just of resistant bacterial agents (where we might consider a combo treatment of doxycycline/ kanamycin to be more helpful) but causes for distension that will be beyond any treatment.
Finally, I know that you don’t want Trevor to suffer and with how advanced his situation is already with dropsy, popeye, corneal damage, and possible ammonia or sepsis marks on his skin, we do have to consider that he is at an advanced point of a disease with a poor prognosis. Therefore, you could consider checking/addressing any ammonia issues, consider a course of kanamycin/doxycycline (which in this country you may need to get a fish vet involved to obtain this quickly), consider an ultrasound or x-ray, but I have to say that I am truly concerned that he is getting to a state where cure will not be possible. Therefore, finally, I do want to leave some information for easing his suffering and euthanasizing him. In case you have not euthanized a fish before, I do want to include a link regarding the use of clove oil to do so (LINK).
Please take care,