Birefringent eyes (not really, but what else?)

Hi, I originally posted this message to sci.optics, but someone there
suggested that I also post here in sci.med.vision. Meanwhile, I did some
google search of sci.med.vision and have seen similar threads in the
past (even back from 1995). Anyway, here is my story, if you want please
comment or maybe just for others to see that double sharp images are not
that uncommon. Thanks.



Hi, I am struggling to understand some problems with my eyes and I need
help.

First, this is just a brief description, I intend to come up in a few
days with details and eventually some simulated pictures.

Description of the problem: at night, when the iris open up, I see a
double image! this happens with both eyes.

RIGHT EYE: there are 2 images, displaced by a tiny angular separation on
the vertical direction. The "intensity" of these images seems about
equal 50-50. I believe the separation angle depends on the opening of
the iris. It seems much bigger in the dark and almost non-existent in
bright sun light.

LEFT EYE: similar to the right eye, except the 2 images are not the same
intensity: the upper one seems slightly dimmer compared to the lower
one, maybe like 40-60 or so. same effect: larger separation at night,
almost no separation in bright sun light.

BOTH EYES: I believe the separation also depends on the wavelength, it
is much worse for blue and smaller for red. I noticed when I go to the
Mall, if I remove my eyeglasses I can still read the red neon signs, but
not the blue ones.

Now I took several eye exams, I tried to explain this to the doctor and
she didn't seem to believe me. I have astigmatic eyeglasses, you can see
the cylindrical lens effect very clearly rotating the eyeglasses by 90
degree. I also remember that for one eye I have the axis at 180 degree
and for the other at 5 degree. I don't have the eyeglasses prescription
handy but this is what I remember.

I also tried contact lenses, and here I can look at the box and quote
the exact numbers:

LEFT EYE: BC: 8.5, SPH: -0.25, CYL: -1.25, AX: 180
RIGHT EYE: BC: 8.5, SPH: -0.50, CYL: -0.75, AX: 180

as you can see, the spherical and cylindrical diopters are different. I
am not sure why both axes are 180, perhaps they don't make contact
lenses with the axis at 5 degree? I will ask the doctor next time I go
in.

Now, it gets even more interesting: I take a lot of pictures with an SLR
camera. I use the left eye, so I close the right eye. After some 20-30
pictures or so, sometimes the right eye feels sore because I kept it
closed, and I get blurry vision with the right eye. now SURPRISE, if I
rotate the eye glasses by 90 deg, I see much better with the right eye!
it's almost like the pressure (keeping the eye lid closed) changes the
defect I have in this eye!


right now as I was falling asleep (1 AM here) I was looking at the alarm
clock (LED display) and studied the effect a little more better. I do
not understand how I can get two *sharp* images without glasses and only
one with glasses!

For a moment I thought is has something to do with polarization.
Wouldn't that be something? so I forgot about sleep, I jumped out of the
bed and took the polarizer from my camera: I played with it, but doesn't
make any difference. so it is NOT polarization. Too bad, if it was
polarization I would be a willing to accept that something inside my eye
is birefringent, although I still don't understand why it is corrected
pretty well with eye glasses (with glasses I have vision 20/20).


Please, if you have had similar experiences, or can offer a reasonable
explanation, share. I simply don't understand this (and I am a Physicist
by the way!)

 

Binaires are not done in this newsgroup and why not the details first when
asking?

Corrected or uncorrected?
Both eyes together, one eye at the time?

A simple explanation and assuming you are not corrected by glasses or
contactlenses (see may request for being more informative at first)
Think about photograpy, the smaller the aperture the sharper the picture
even when not having the lens exact focused.
The more light, the smaller the pupil.

See above at first, maybe I respond later on the differences.

This is quit normal for slightly myopic as you are.
Blue light is refracted more as is red light.
A myopic has his image focussed in front of his retina ,the receiving plane
like the film or CCD plane in camera's.
The blue light more away from the retina and the red light some what closer
in front of the retina.
The red neon signs are more focussed to the retina and thereby more sharp
''catched'' by the retina.

The simple explaination for this is the astigmatic part (cylinder) in your
prescription.
Those images are NOT as sharp als the single image when corrected and when
looking at an object in the long-distance!

If you are, try some explanations on cylindrical optics.
In one direction no refracting and in the other (90 degrees turn) the
refraction of the cylinder power.
A spherical glass has one focus point at one place so to say and a cylinder
glass has two focal lines at two different focused places.

Jan (normally Dutch spoken)

 

I will not post binaries. I was thinking to post the pictures on the web
and post the *link* here.

uncorrected ("naked" eye)

One at a time. With both together the images don't overlap very well, so
there are like 3 or even 4 images...

OK, I do understand what the prescription means, I do know about
cylindrical and spherical lenses (and much more). What I do not
understand is what that BC stands for? OK, maybe those split iamges are
not as sharp, but they are reasonably sharp.

Still, I don't understand how you can get 2 *split* images. there were
some interesting replies in sci.optics group.

 

The (B)ack(C)urve of the contactlens.

They are because your basic myopia is not that high.
OD (right eye) S-0,25 diopters wich is nearly no error.
OS (left eye) S-0,50 diopters also not that much of an error.
Without the cylinder part so to say not much of an error.

May I try it simple?
Take two prisms and hold these with the base against each other and the line
in between horizontal.
This is not exact your astigmatism but maybe you get my point this way.
What should you aspect looking through the prisms to an object?
Okay, two images of the object instead of one.
You correct this by placing two prisms of the same power but now attached
with there tips against each other and again the line in between horizontal
in front of the first pair.
You may take the second pair of prisms being your correcting cylinder.
Of course an astigmatism and a cylinder are not the same as two prisms but
knowing you are a physicist I take it for granted you did recognize the
similarity.

Is this helping you out?

Jan (normally Dutch spoken)

 

I had a look in this newsgroup regarding your question.

A lot of answers overthere are NOT pointing to your question.
Remember you are having NO double images when being corrected with glasses.

Jan (normally Dutch spoken)

 

yes, in this case I expect 2 images. but again, the "double prism"
object has a sharp edge, while (i hope!) all the surfaces in my eye are
smooth (second derivative finite). It's a good analogy, but I wanted
more. Don't get me wrong, I like your contribution and I do sincerely
appreciate your effort.

yes it does. Thanks!

Chibitul (normally Romanian spoken here)

 

Think about an American football, not a sharp edge and having two curves,
one with a short radius and the other a longer radius.
Simply said, cut out a circle of the football at the longside and there you
have your not equal in radius cornea without any sharp edges.

In other words, two smooth curved prisms.

Look at the character O at the long-distance placed and regognize the top
and down part is not as sharp as is the right and left part.
Reread me earlier explanation about the two lines a cylinder focussed at two
different places on the optical axis.


Jan (normally Dutch spoken)

 

Mike, he does not have monofocal diplopia when wearing glasses.
I might think corneal irregularities are not the matter in this case, don't
you agree?

Jan (normally Dutch spoken)

 

Excuses for me mistype, indeed I meant monoculair instead of monofocal.

They have in an absolute sence and I am familiar with all the aspects.

What happens however when you put a cylinder axis 0 in front of an
ametropic eye corrected to zero error with an RGP contactlens ?
You get two disturbed images above each other.
This is what happens in the case of Chibitul when he is not wearing his
glasses.
The irrigularities of the cornea are not the major cause to me opinion.
If they are, Chibitul should have some disturbance too being corrected with
glasses and having his pupils dilated.
I bet he has not.

Than it shows even when corrected with glasses.

Jan (normally Dutch spoken)

 

Hi Jan and Mike

It is possible that he has present in the lens of the eye(s) a bi-prism. I
had left monocular diplopia for some years, disappeared about 10 years ago.
At The City University, where I trained it was diagnosed as a lenticular
bi-prism. A paper on the condition exists, my copy vanished long ago, I
think it was authored by H.H. Emsley in the 1950's

As my lens thickened with age the diplopia vanished.

Hope this idea helps

Regards


Ian Hodgson - Isle of Man

 

Hi Ian,
The matter in question, not wearing his glasses two images, wearing glasses
one image.

Mike and I have different ideas what should be the main point, normal
astigmatism of the cornea or irregularities of the same cornea.

A bi-prism in the lens crystallina gives a double image with or without
correction I should say.

Thanks for the help and with regards.

Jan (normally Dutch spoken)