Get 'shaded' glasses - dark on top, light at the bottom.
That way, you have protection from the sun outside,
but normal light in the cockpit (in the shade).
Your eyes don't have to take time to accomodate to
the different light levels.  Helps take some of the
pain out of the ageing process.

Works well both at high noon and approaching sunset
(westbound) - sometimes I forget to take them off
(part of the ageing process, too).

Dick Reeve
L2K-233 (65% headed for 55%)
Anchorage, AK