This drug accumulates in various tissues, so for retinopathy what matters is the cumulative amount of the drug consumed over time.

oh man ! just like excess of vitamin-d can lead to vitamin-d toxicity, so can this. in my naïveté, i was assuming that excess of it would be just flushed out.

Its concentration in lung can be 100 times or more of that in serum. This may be helpful for its efficacy against the virus.

only if everything gets stored, and there is no chance for that

The risk is for cumulative (not accumulated) dose:

has a cumulative dose of more than 1000 grams

And the calculator they link out to gives the same number I calculated.

A kg isn't necessarily that much over a lifetime. I'm over that with at least one drug.

taken over the years