Similar to caps lock being ctrl when held and escape when tapped, I set up return to be ctrl when held and return when tapped. Nice keyboard symmetry this way too.

Progressive lenses need much more accuracy to be fitted correctly. This means a mono-PD (separate PD for each eye, not just the distance PD halved) and also a height, usually from "datum" measured for each eye too. This measurement would be different depending on the frame and how it sits/adjusted to your face.

This means the frame must be chosen and fitted to you before any of these are measured.

It becomes a 2D measurement.

There is a lot more to it (vertex distance, pantoscopic tilt etc) but the above is the absolute minimum.

Single vision lenses are always going to be better at that one thing than anything else which tries to cater for all (or multiple) distances, at the expense of everything else.

I also agree with educating yourself to protect yourself. However, there will be many holes in your research which a good optometrist should be able to fill in. Together you can make the best choice.

One area I never see discussed, especially from the "I can find my own prescription" crowd, is binocular vision. How your eyes work together at certain distances and with certain tasks will determine not only which prescription you need but also how the spectacles are set. I'm not only talking about setting the PD and lens height (which may need to be different for your right lens compared to your left, at different at all distances). There are many more considerations such as vertex distance, pantoscopic tilt, frame choice, lens material, wrap angle etc.

Sometimes the optical centration is intentionally different from the PD to induce prism to decrease eye strain. This is not uncommon with complex prescriptions and in the older population.

And sometimes there are other solutions such as vision training. Not the woo woo Bates method, but real vision training used to fix real problems.

Good optometrists provide a lot of value. There just way too much information and most patients will be happy to just let them do what is needed.

And sometimes you just need to get off the PC for a bit.

Yes, I have a great optometrist who provides a ton of value but I only get a certain window with them which at Berkeley is about an hour which is a lot. And I got an awesome prescription from them.

But optician (!= optometrist) generally want to talk to you about frames and not about lenses. This is understandable since they have to make a buck.

So the gap filler here is educating myself. I still let them do what they are in fact very good at but I educate myself on the choices.

This has worked out very well for me. My sister in law has terrible vision and I wonder whether my approach (self-education) would work for her. Maybe, maybe not. But I do think she should get personalized free-form lenses and her optician hasn't suggested that. Dunno why.

I've talked to a ton of people about their phones and apps. I've never talked to someone about lenses. That's strange.

Your pupillary distance won't change depending on the frames you buy (it is a body measurement after all).

However, where the optical centre of a lens is placed within a frame can vary from the PD a fair bit, depending on how the frames sit on your face, as the contact point of the frames do not always line up perfectly with the top of the nose bridge.

Also, an oft looked over measurement is the distance from the bottom of the frame to the centre of the lens, which is important with complex prescriptions and cannot be measured without looking at the frame on your face.

Having said this, with most low prescriptions the human tolerance is so high that it does not matter.

Generally, you would expect lenses with a higher refractive index to be thinner.

However, due to the selling point of Trivex being "shatter proof" it has a greater centre thickness (to pass safety lens regulations), and thus the edge thickness is also comparable to CR-39.