Re: Birefringet eyes (not really, but what else?)

From: Repeating Rifle (salmonegg_at_sbcglobal.net)
Date: 07/29/04 

Date: Thu, 29 Jul 2004 18:14:11 GMT

in article chibitul-553527.00512729072004@newsclstr01.news.prodigy.com,
chibitul at chibitul@eudoramail.com wrote on 7/28/04 9:51 PM:

> 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
> RIFGT 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!)

I indeed have observed similar effects but with more images. I have called
it a fly's eye phenomenon. Although I have a very good understanding of
optics, I do not fully understand what is happening.

What I think is happening is that your cornea and lens system consists of a
number of side by side "lenslets" misaligned from on another. Each lenslet
creates its own image. When the eye is uncorrected, each image on the retina
is displaced from where it would be if the focusing were provided by a
single lenslet across the entire eye.

Try punching about a two millimeter hole in a piece of opaque paper. At
night, when you iris opens, view distant lights through this hole with the
*** place close to your ey. Then, transverse the piec of paper to see if
the image chnges as you use separate parts of you cornea for focusing.

Bill

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