Oleg- I know exactly what you are talking about. We don't see it very often, but often enough to understand your concerns. Sorry to be the bearer of bad news, but unfortunately, virtually all of the time, the condition turns out to be fatal. I really don't know what it is, but it does not seem to be contagious, especially the pop-eye part. The pimples or white spots you mentioned just seem to get a little larger, then the fish turns almost black, and usually dies within 48 hours after that. Some breeders say that it is due in part to water quality. While that may be part of the problem, I don't believe that it is always the root cause. We do 80% water changes once or twice a week in our grow-out tanks, plus we have fully functioning filters in each of our tanks, and every once in a while one of these symptoms pops up (no pun intended). In our case, more often than not, it can usually be traced back to a sudden drop in temperature. We also raise discus, and many times we will keep discus and rams together, as they both like the water around 84-86 degrees. Living in the Chicago area (especially this year) we are subject to pretty strong thunder/snow/ice storms that will knock out our power for a long time. We have a generator for the fish room that can run the pumps and filters, but doesn't generate enough electricity to power all the heaters. If the temps in our tanks drop into the 70's for more than a few hours, we may have problems. Even if we bring the tanks back up to normal temps pretty quickly, the fish, rams especially, seem to get chilled and become subject to secondary infections. The discus, being larger and more hardy (yes, discus are pretty hardy) do not seem to be affected by the short-term drop in temps. The other interesting thing about these symptoms is that even though we also breed angels and discus, we have never seen any of these symptoms show up in any other species of fish other than the rams. I don't know if they are just more sensitive than some of the other fish.
I'm not an expert, but just from our experience, these secondary symptoms will not show up for days or even a couple of weeks. Could it be iridovirus? Possibly, but since no one has been able to demonstrate a direct connection between the virus and these symptoms, and we don't own an electron microscope, we may never know. That, plus the fact that there is no known medication for treating viruses, makes it difficult to identify or treat. We have never kept gouramis in any of our tanks. We run a closed system, rarely bringing in fish from outside sources. When we do, they are QT'd for at least a month before introducing them to our other tanks. Thinking that these symptoms may have been bacterial or fungal, we have tried a wide variety of medications, including those previously mentioned in other posts, including medicating their food, but it seems that once the white spots or the dark coloration begin to show, it's usually too late and we have to remove the fish from the tank.
Hopefully, someone else will have some other ideas.