I would call your doc asap and report it, to get it on the record if nothing else.

Here's a couple of long anecdotes that basically illustrate how visual distortions in ET patients can manifest in different ways and may not be related to ET or meds at all:

I went blind in one eye one afternoon when I was teaching, at age 59. Chalked it up to a migraine aura, but had a "shadow" in my peripheral vision for weeks after that episode. A year later, I was diagnosed with ET.

I mentioned the visual episode to the hematologist. She said, "Hmm," but since I had no stroke symptoms like numbness and it went away, she didn't think it was worth investigating.

I do get a more typical migraine aura very occasionally (maybe once a year), usually without the headache, but with nausea and the brain fog that follows. Current hemo says she doesn't know if it's ET related, especially since my mom, who did not have ET, had frequent migraines.

Dad also had ET and before his diagnosis was always asking me, "How many ducks do you see in that picture?" Or "How many apples do you count in this bowl?" He said he had trouble "seeing the whole picture."

We didn't know then that visual distortions were part of the ET landscape, so he just figured it was "old age."

Dad's visual distortion was a constant for him whereas mine cleared up. Neither Dad nor I had any sign of stroke with these visual distortions.

I did not noticed that the HU made any difference in my migraine symptoms. Dad's visual issues did not clear up after he started HU.

So I have nothing conclusive to offer except that, yes, ET patients have weird visual episodes.