If you don't see a difference, you are already very close to the optimal correction and a subtle change in either direction is unnecessary. They will still go ahead and try fine-tuning the prescription and when you tell them that A and B are the same, they can fall back when they add another correction. A and B might currently be the same, but if you add C, A+C could be better than B+C.
You know, it makes me wonder how that works. Because most of the time, they get the prescription right, even though, for the most part, we only guess which one feels right to us, even though, to us, one and two look practically the same.
I think part of the image processing is done subconsciously and so we can pick up the minute differences in image quality by feel, even when we can't say what exactly is different.
That makes sense. Our subconscious is better at picking up the small details than our conscious mind, because it takes more effort for us to think about it. That's why they say "go with your gut" because our brains calculate things subconsciously. It's why we can do things without thinking about it.
I've always assumed it is because the limited amount of calibrated lenses. A random example, you might see the same with 0.4 and 0.5 because you need a 0.45.
My guy doesn't do this except for a quick sanity check. Or maybe because patients expect it? They have your prescription the second you look in the auto focusing machine. Hell, someone invented a lens for a cell phone that does it.
The optometrist is looking at your eyeball health and related medical issues. The clicky thing is mostly performative.
Hi I'm an ophthalmologist. The auto refraction is good for a baseline, but the manifest refraction is necessary for the best prescription. Also lots of things can affect the auto refraction like dry eyes, cataracts, and macular degeneration.