Speaking of Vision -- How 'bout Progressive Bifocals?

Jay Honeck wrote:
Great stuff, Randy -- thanks.

I guess I don't understand this part:
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Progressive lens design
In order to create a no-line progressive lens, there are two large areas of
the lens that you cannot see through. Imagine what an hourglass looks like.
This is the shape of the area of the progressive lens that you can see
through. Objects seen through the areas of the lens to the left and right of
the narrow middle section are highly distorted and you cannot see through
them.

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Why would the areas to the left and right of the middle section be "highly
distorted"? Why aren't those areas simply made to your "distance"
prescription?

I don't fully understand the optics, but that's exactly what my
optician (who's a fellow pilot) explained to me, and when I got my
progressives, that's exactly what I experienced. I couldn't stand it,
and had him re-make the lenses as lined bifocals (which I'm still
struggling to get used to).