1) that machine is a godsend; I have keratoconus (mis-shaped eyeball caused by thin corneas), and it’s incredibly hard for a doc to get the prescription right without having this machine give a starting prescription.

2) I think a good optometrist is trained for the fact that your assessment is subjective. I’m pretty sure my optometrist goes through the best 2-3 a few times when he’s close just to confirm he’s gotten it right.

3). To add the others’ comments, don’t feel obliged that one of the two choices has to be better. If they’re similar, say so. Or if one is just barely better, the fact that they’re very close is helpful to the doc too.

4) the technical term for the machine is actually “the red balloon machine” (/s)