Phoropter. That’s what this instrument is called.
My optometrist told me this as I photographed it. She was relieved I didn’t ask her to be in the picture because that’s what most people ask. In fact, no one ever had taken a photo of _just_ the device before.
She once informed a young patient that it was called a phoropter and he thought that sounded cool like a dinosaur.
As for me? Still near-sighted. I have at least a year before needing bifocals, but my distance vision got worse. New specs soon.