Sandie,

Short answer- about 10% to 20% thicker.

Longer answer- there are many ways to make thinner lenses, as opposed to just
selling you the "thinner ones".  The thickness (and weight) of the lens is much
more dependant on the size and shape of the lens/frame, the type of bevel
(rimless is thicker in your Rx), lens design; ie, base curve/asphericity and
prism thinning, than by the index of refraction of the lens material alone.

So, with your Rx, you won't see too much difference in appearance between
regular plastic and a moderately high index lens like polycarbonate, about 10%,
if the only difference is the lens material. There may be a noticeable
difference in weight though, which usually gives me more concern than the lens
thickness.

Hope this helps,  

Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
- Richard Feynman