If you live long enough, your ability to adjust the focal length of your eyes will decrease and the eye doctor will try to sell you a pair of bifocals.
There is an old fashioned type that has a little panel in the bottom. It seems like this would be a disturbance in the field of view, so I chose instead the “progressive” lenses, which have a different focal length in that region, but the transition is not sharp.
Immediately I regretted the choice. One learns to move ones head up and down as one reads, but the effect is not as good as reading glasses. I suspect that the advantage of the progressives is that other people can’t tell you’re wearing bifocals. But glasses are expensive so I suffered until it became time to get a new pair.
So this time around, I picked up two pairs, “reading” and “driving”. The only difficulty is that I now have to carry an extra pair around with me, and this is an expensive thing to lose.
However, there is another way, something that the ophthalmologist won’t tell you.
If you are near-sighted, you can adjust the effective focal length of your eyes + glasses system by adjusting the distance from your eyes to your glasses. You can use your “driving” glasses as reading glasses if your nose is long enough to support them. Fortunately, nature conveniently arranges for the human nose to continue lengthening during life, thereby counteracting the diminution in focal adjustment.
Next time around I will get the reading glasses adjusted downards in prescription so that in the usual position they work in intermediate distances, and can be adjusted down my nose for reading. I will call them my “TV” glasses.
I suppose these things should have been obvious to someone with a Master’s degree in physics. However, I managed to get into physics grad school without an undergraduate education in physics. This left certain gaps in my education, most notably in optics, but also in things like thermodynamics and E&M.
My intuition tells me that if I were far-sighted, I would still want an intermediate pair of glasses, but that sliding them down my nose would allow me to turn them into driving glasses.