Very nearsighted, and have hiked with bifocals for years with no problem. But they are ‘excecutive’ bifocals, with a straight line between the upper and lower portions of the lens. For hiking, you might want to have the lower portion slightly larger (move the line up a bit), because in rock fields, a clear view below is not just convenient, it is essential to avoid a serious fall.
As impairment increases with age, the difference between reading distance and eyes-to-ground becomes more acute. For example, a special lens with an in-between prescription is used for the computer, but does not work for watching TV or reading a book. If you haven’t reached this point, one lens that allows a focused view of the ground, and an acceptable but not great view of objects in the distance (so do not use for driving), might work.
Matthew may have a point also with ‘optical centers.’Â This is not pupillary distance, and can’t define it, but know it can make the distance between glasses that are comfortable to see with and those that are definitely not.
Most eyeglasses are purchased from the cheap sources mentioned in this thread, which are fine if they work. For someone with more acute vision issues, they often do not work. I’ve always had to hunt for skilled eyedoctors who can put all the factors together and produce glasses that work. A good one sent the glasses back four times because the lenses did not conform to her specs, including those for optical center. Went to Walmart once, had an exam by their eyedoctor, and despite 4-5 attempts, they all looked like looking through a fish bowl. That is because most glasses are filled with lenses that are mass produced.
And you might have something really wacky, like having to lower the pupillary distance on the glasses from what it actually is to prevent double vision.
As with all types of doctors, finding a good one is critical. Word of mouth is very helpful. Good luck.