> As a doctor I know some things about the human eye so I understand how to use those lenses. However, I have no clue about the magic ritual of the optician (“Do you see better with this lens?” - selects random lens and holds it in front of my eye). >Luckily, I didn’t have to. There's a specific reason why they do this and ask you to make a decision in an instant. It's called accommodation. Your eyes will quickly try…
Yes, I am a doctor. As far as I remember, I studied medicine and graduated. As other comments point out, medicine is a very specialized field nowadays and I didn't specialize in any field (I got into coding healthcare software instead) - in Germany you study all disciplines at University (min. 6 years) and then specialize during something comparable to US residency in a hospital. I understand the process of accommoda…
Also cyl/sphere differential is also hard to determine but often follows a pattern in that you can overcompensate in sphere for cyl and vice versa.
Not even going to begin to go into the effects of possible tolerance differential, prism imbalance, and that is just with Single Vision Lenses.
Also you generally have 90 days as industry standard to go back and retest your RX.