DW> I thought about that. But the clip-ons would prevent the main
 DW> lenses from darkening, so what's the point of paying for
 DW> them?

It's a matter of preference and economics.  The clip-ons are great in the
car, the photochromic lenses are great outside the car.  Personally, I
enjoy the freedom of not having to carry the clip-ons around, and attach
(unattach) them every time I go outside (inside).

 DW> But if I had photochromic lenses,
 DW> I'd have to wait for them to clear, which again would take a
 DW> few minutes. Right?

Well, that delay is short enough that it never bothers me.  Others, though,
don't like it.  The only way to know is to do as you have, and try it.

 DW> Recently, I have noticed that I am less aware than I should
 DW> be of things out in the periphery of my vision when I'm
 DW> driving. After visiting the eye doctor, the reason is
 DW> obvious. My glasses are progressive bifocals with positive
 DW> prescriptions. Since the old ones were too weak, I was
 DW> unconsciously looking through the lower parts of the lenses
 DW> so as to get some extra power. But the field of vision lower
 DW> down is much narrower than it is at the top, so my peripheral
 DW> vision is blurrier than it should be.

 DW> The new glasses should fix that...

Progressive bifocals have poor correction in the periphery, even at the top
of the lens.  It's a well-known problem.  The more you pay, though, the
better the peripheral vision portion of the lens.  It's a trade off that
some people don't like, so they go with non-progressive bifocals, or even
trifocals.

Monovision is another alternative.  One eye is used for far away vision and
the other for close up.  This can be accomplished with contact lenses or
surgery.  I have a co-worker who is in her seventies and has never had to
have any type of vision correction.  She's far sighted in one of her eyes
and near sighted in the other.

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