I also don't know what it is, but from the beginning it did not look like ick. The fact that is was on both eyes and nowhere else spoke against it (ick spots are never symmetrical on a fish), and also the eye lens rarely gets ick spots; I have never seen ick in eye lens tissue, even in heavily ick-affected fish.
I believe the condition was already present when you acquired the fish (a week+ ago). What do you know of its age, and of the conditions it was in?
What is confusing is why it has grown so fast in such a short time, particularly with your description of water change routine and level of nitrate. It looks similar to conditions that occur in old (age) fish), as well as in other animals (dogs and people, for instance), but of course if could also be a bacterial infection. Again, the confusing part is that typically such conditions develop slowly, not in a week period. I too had an older angelfish who developed something like that, but it was in only one eye, and progressed over a long period of time. The fish lived several more years normally, and none of his tankmates (including angels) developed the condition.
Considering that your fish is acting normally and eating, I would do nothing more than maintaining excellent water quality, and providing good food, but not too much, but of course I would continue observing for other changes. But that is me.
Among my silver dollars (Metynnis maculatus), I have a ~22+ year old male who came to me with a severe case of popeye (exophtalmy), cataracts, and white blotches on his body (first set of pictures except the top left, which is a female of the species). After 3.5 years (single photo below), he is a beautiful, active and healthy fish, the largest of my troup; he continues to be slightly buggy eyed, but is quite healthy and could possibly live 1-2 more decades into the future.
Good luck!
