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Images of visual distortion
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Gary
medicine forum beginner


Joined: 18 Nov 2005
Posts: 21

PostPosted: Fri Jul 14, 2006 9:46 pm    Post subject: Re: Images of visual distortion Reply with quote

Quote:
The intent of your question is not clear.

To clarify, I was looking for examples of the effect when *viewing through
glasses when correcting* varying degrees of myopia, hyperopia and
astigmatism. I'm not wishing to simulate or see examples of it because I'm
unaware of the effects, I was just hoping to see the effects such as
minification and geometric distortion.

Regards
Gary
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Quick
medicine forum Guru


Joined: 19 Jun 2005
Posts: 343

PostPosted: Fri Jul 14, 2006 6:46 pm    Post subject: Re: Images of visual distortion Reply with quote

otisbrown@pa.net wrote:
Quote:
Also a good "picture" can be found at:

http://www.nearsightedness.org/

Otis

That's great. Can I add my reefer madness clips
to the bottom?

-Quick
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otisbrown@pa.net
medicine forum Guru


Joined: 24 Mar 2005
Posts: 1447

PostPosted: Fri Jul 14, 2006 6:41 pm    Post subject: Re: Images of visual distortion Reply with quote

Dear Gary,

The intent of your question is not clear.

If you have normal 20/20 vision (refractive state from zero to +1
diopters),
then you can SIMULATE 3 diopters of myopia by simply wearing
a +3 diopter lens. That is the level of "blur" a -3 diopter myope will
see in the distance, as well as the approximate "blur" on his Snellen.

If you have a refractive state of zero (and 20/20) and wish to simulate
a refractive state of +6 diopters, then the APPROXIMATE method
would be to get a -6 diopter lens -- and wear it. If the person is
young, however, his accommodation enable him to see through
the +6 diopters.

To simulate astigmatism (assuming you have none), then
just get a cylender lens of -2 diotpters, and wear it.
If you have a trial-frame, you can rotate the lens through
an angle from zero to 180 degrees.

Hope this helps clarify these issues for you.

Best,

Otis



Gary wrote:
Quote:
Is there a site with photos of, or program that simulates, the effect of
correcting particular levels of myopia, hyperopia and astigmatism when using
glasses?

TIA
Gary
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Mike Tyner
medicine forum Guru


Joined: 24 Mar 2005
Posts: 1299

PostPosted: Fri Jul 14, 2006 4:25 pm    Post subject: Re: Images of visual distortion Reply with quote

"Gary" <gary@franklin49deletethisbit.freeserve.co.uk> wrote

Quote:
Is there a site with photos of, or program that simulates, the effect of
correcting particular levels of myopia, hyperopia and astigmatism when
using
glasses?

Otis didn't answer the question you asked. You asked the effect of
_correcting_ myopia, hyperopia and astigmatism.

Correcting these conditions with spectacle lenses produces minification
(nearsighted glasses) and magnification (farsighted glasses) and a related
nonlinear effect called barrel or pincushion distortion. I don't recall an
illustration with glasses only. You can probably google "pincushion barrel"
and see diagrams of those conditions.

With low prescriptions, these effects are pretty minimal.

If you meant to ask the effect of _being_ farsighted or nearsighted, you can
try someone else's glasses to get an idea.

If you wear a nearsighted person's glasses you'll see what farsightedness is
like.

If you wear a farsighted person's glasses (or drugstore reading glasses) you
see what nearsightedness is like.

If you wear glasses made for someone with substantial astigmatism, those
lenses will create astigmatism in an individual who doesn't have any (only
while they're worn... it doesn't change the eye.)

-MT
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otisbrown@pa.net
medicine forum Guru


Joined: 24 Mar 2005
Posts: 1447

PostPosted: Fri Jul 14, 2006 3:45 pm    Post subject: Re: Images of visual distortion Reply with quote

Also a good "picture" can be found at:

http://www.nearsightedness.org/

Otis



otisbrown@pa.net wrote:
Quote:
Certainly, Gary, try:

http://www.preventmyopia.org/animation.html

Best,

Otis

++++++++


Gary wrote:
Is there a site with photos of, or program that simulates, the effect of
correcting particular levels of myopia, hyperopia and astigmatism when using
glasses?

TIA
Gary
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otisbrown@pa.net
medicine forum Guru


Joined: 24 Mar 2005
Posts: 1447

PostPosted: Fri Jul 14, 2006 2:03 pm    Post subject: Re: Images of visual distortion Reply with quote

Certainly, Gary, try:

http://www.preventmyopia.org/animation.html

Best,

Otis

++++++++


Gary wrote:
Quote:
Is there a site with photos of, or program that simulates, the effect of
correcting particular levels of myopia, hyperopia and astigmatism when using
glasses?

TIA
Gary
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Gary
medicine forum beginner


Joined: 18 Nov 2005
Posts: 21

PostPosted: Fri Jul 14, 2006 11:38 am    Post subject: Images of visual distortion Reply with quote

Is there a site with photos of, or program that simulates, the effect of
correcting particular levels of myopia, hyperopia and astigmatism when using
glasses?

TIA
Gary
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Google

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