G'morning David, 

 DW> If I don't wear any kind of shades outdoors, it takes
 DW> my eyes about 15 minutes to become fully adjusted to
 DW> the darkness.

Adaption should take about 10 minutes for your cones and up to 40 
for your rods, and is triggered off by a third type of light- 
sensitive cell in your retina that reports the difference between 
daylight and nightlight ... 

 DW> If I wear shades outdoors and remove them as soon as
 DW> I go in, I can see reasonably well right away. But if
 DW> I had photochromic lenses, I'd have to wait for them
 DW> to clear, which again would take a few minutes. Right?

Err... it might be hard to find any kind of shade which puts you 
into night-light mode in broad daylight - and still allows you to 
see where you're going usefully...

 DW> Recently, I have noticed that I am less aware than I should be of
 DW> things out in the periphery of my vision when I'm driving. After
 DW> visiting the eye doctor, the reason is obvious.

Glad to hear that - drops in peripheral vision can indicate the 
outset of glaucoma, I seem to recall...

 DW> The new glasses should fix that...

Mine have arrived and are requiring the head to learn new tricks 
all about - very annoying but hopefully eventually good;  I can no 
longer look straight ahead to read this screen - the head needs to 
adapt to an attitude that feels like the one a racing camel adopts 
for maximum speed....

:-(
 
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