In article <31FE08C8.27B1@simmons.swmed.edu>, walberg@simmons.swmed.edu says...

>Bob Neuman wrote:
>> Thinking about this a little more, it occured to me that, due to the
>> structure of the eye (roughly a sphere, with the single-element lens
>> near [but below] the surface, and with the image projected onto the
>> roughly hemispherical "film plane" with its forward edge not in the
>> same plane as the lens [I trust this description is not in error!]),
>> the perspective would not be completely of the spherical (fisheye)
>> type, though it would be much closer to it in characteristics than
>> to the rectangular type.

>Don't forget that the optical signal recieved by the retina is
>extensively processed before it arrives in consciousness. I've
>recently noticed a result of this processing that actually kind of bugs
>me. I got glasses a year ago that helped correct my astigmatism. I'm
>sure that the glasses also have a few other effects that the opticians
>think make people like their glasses. Anyway, after a year of
>wearing them all the time, I notice that when I take the glasses off,
>the shape of the world changes. Objects that appear round with my
>glasses (and are really round, and looked round to me before I ever
>wore these glasses) look like ovals with the glasses off-wider side to
>side. For example, I can turn a dinner plate around, but it always
>looks wider side to side. It looks round again with the glasses on.
>Leaving the glasses off a while doesn't fix it. So, my eyes get the
>same signal, but it arrives in consciousness differently because it is
>now processed differently than it was before I wore these glasses. It
>is kind of funny. Now that I'm aware of it, I notice that people look
>a bit fatter when I have my glasses off.
> So, back to Bob Neuman again, I was wondering how your brain is
>going to deal with the multiple different points of view that your new
>glasses provide. Do any parts of your glasses change the roundness of
>things?
>Mark Walberg walberg@simmons.swmed.edu

You bring up an interesting point - we do process the information obtained
from the eyes (see long exchange with "SpaceMan Spiff"), though it can be
shown that we leave some of it relatively alone (like perspective....).
I have astigmatism, also, but it must be milder than yours, since I do not notice the proportional shift when removing my glasses (I would guess that
it would shift in time for you back to "normal" if you went without glasses
long enough....). My glasses curve straight lines that are off center,
making fisheye perspective more "normal" for me, I suppose (though I can
see some curvature without glasses, so I know that I actually do see in spherical perspective [there are other indicators, also]). Here may be a
couple of examples of the effects of processing: seeing reversed colors
when looking at white after staring at strong colors (most would argue
another cause....); or seeing reverse motion on a hillside after staring
at a waterfalls.
Hope This Helps