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Physics of a visual impairment

  1. Jun 22, 2017 #1
    I am not sure of the right group for my question.Medical seems like a place to start.

    ----

    I am monocular with an advancing cataract and macular pucker.

    Glasses with a corrective plastic lens help me see somewhat better.

    A pair of tinted No IR UV shields in front of the glasses sharpens my focus further.
    They improve contrast. The tint is about 50% transmittance, orange.

    Another plastic lens, clear, in the front of those two, like safety glasses or clear NoIR UV shields, sharpens my focus even more.

    None of my treating professionals have a clue why such stacking of plastic lenses improves my vision. My guess is there is an answer in the physics of optics?. Perhaps collimating the light more with each lens in the stack bring greater clarity?


    The improvement happens with both print and screen reading.


    I found some explanation in microscope notch filters, namely the “optical density” of a filter. If I understood it correctly increasing the concentration of the filter dye and or increasing the thickness narrows the notch. A sharper notch mean sharper vision? I also thought that the stack is increasing the UV blocking too?

    The practical side of my physics-curiosity lies in finding solutions that will help me see better as my vision further decays – and - keep out of risky surgery for as long as possible.

    Thank you for any thoughts, suggestions, and guidance.
    Michael
     
    Last edited by a moderator: Jun 22, 2017
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  3. Jun 22, 2017 #2

    berkeman

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    Welcome to the PF Michael/Michasel. :smile:

    Sorry, but I need to close your thread temporarily for Moderation so the Moderators can discuss it. It would help if you could send me information about this part of your post:
    Please click on my avatar and start a Conversation with me to send me information on the professionals you have been seeing. We need to know their qualifications (Optometrist? Ophthalmologist? Other?), and what they have said in response to your questions. Thank you.
     
  4. Jun 22, 2017 #3

    jim mcnamara

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    Unlocked the thread. @Andy Resnick may be able to help you. I cannot, do not know enough to make sensible answers. We cannot prescribe or suggest any treatment whatsoever.
     
  5. Jun 22, 2017 #4

    Evo

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    Did you ask the optometrist that made the lenses why they made them this way? They might know the answer since this is their line of work. They would be the ones to ask, not your doctors.

    There are many weird things that affect vision. For example, I am nearsighted and unaided, I cannot see the time on the digital clock on the TV across the bedroom at night but if I pinch my thumb and forefinger together to create a small space to look through (the same effect can be created by making a tiny circle to look through) I can see the numbers perfectly clear. This is a very well documented effect.

    https://www.thenakedscientists.com/forum/index.php?topic=41293.0
     
    Last edited: Jun 22, 2017
  6. Jun 23, 2017 #5

    BillTre

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    This is a complex issue. Here is some information I found.

    Main components:
    cataracts: opacity in the lens. An opacity in a lens in an optical system can result in the light going through the lens being scattered and therefore not forming a cleanly focused image as a lens normally would.

    macular pucker: the macula is a central area of the retina where there is highest acuity and color sensitivity.

    Protective, optical, and sensory functions may all be involved in your situation.

    I had to look up "No IR UV shield" since I had never heard of it before.
    Here is a rather informative page from a company that makes some of these shields.
    The "No IR UV shield" seems to act as a filter and removes IR and UV wavelengths from the light reaching the eye.

    Protective:
    The IR wavelengths are thought to be "associated with eye fatigue."
    The UV wavelengths are thought to be involved in cataract formation as well as having negative effects on the retina (along with blue and green wavelengths).

    Optical:
    Glare (due to light scattering in the lens) would scatter some of the incoming light inside the eyeball instead of using it to form an image on the retina. This would reduce the the image to noise ratio and therefore reduce contrast.
    If the cataract opacity interacted only (or preferentially) with certain wavelengths of light, than those would be preferentially scattered. Removing the scattered wavelengths could reduce the noise and increase contrast.
    Glare can also mean a bright light source is making less bright parts of the image indistinguishable (see retina function below).

    Retina function:
    I am not clear about the optical density filters you mentioned, but the macular pucker implies to me an impairment of retinal function. The retina not only transduces light into neural signals, but also has some information processing functions, perhaps including contrast enhancement and dealing with different illumination levels. These function may not work as well as they used to. The neutral density filter may just reduce light levels to something your retina is more able to deal with.

    All this is speculative on my part.
    If it were me, I would go to your doctors and/or optometrist and ask them pointed questions based on ideas like these and see what they think. I have found the medical people are often more informative when asked questions based on the patient's understanding, since doctors are often unaware of their levels of knowledge and their issues of concern.
    Also make them explain any jargon they use. It is not reasonable to expect patients to understand the specialized terms of the medical world. It is lazy to use jargon with people who don't understand those words.

    If your eye wear is filtering out blue light you might not be able to distinguish the blue type indicating the links I put in, since they are blue.
    I am therefore relisting them below:
     
  7. Jun 23, 2017 #6

    Ygggdrasil

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    My speculation as a microscopist:

    Many lenses are imperfect and one type of imperfection is called chromatic aberration, meaning that different colors are refracted slightly differently by the lens resulting in slightly different focal points for different wavelengths of light. For a lens that exhibits chromatic aberration, when you get a red object in focus, a blue object would appear slightly out of foucs and vice versa. Therefore, by limiting the spectrum of wavelengths that pass through the lens, you may be minimizing the effects of chromatic aberration, making images appear sharper.
     
    Last edited: Jun 23, 2017
  8. Jun 28, 2017 #7

    Andy Resnick

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    No clue.
     
  9. Jul 2, 2017 #8

    Tom.G

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    It is common (universal?) for people with moderately advanced cataracts to report a yellow tint to neutral colored objects, such as the Moon. Here I define "moderately advanced cataracts" as sever enough that the halo around the moon at least triples the total diameter.

    (Admittedly the above is from a limited sample of four, myself included.)
     
  10. Jul 2, 2017 #9
    You might want to check out " rating system cataract."

    I wear 50 transmission orange tint UV shields because they knock down glare and improve contrast. As a result everything looks yellow, but I the benefits way offset the color imbalances.
     
  11. Jul 5, 2017 #10
    When you actually look at a clouded lens, they will typically be a sort of greyish-tan color, as Yggg stated, which would likely selectively alter those wavelengths more than others. The reason a pinhole works for the eye is that you limit light input to a narrow portion of light coming in to the most perpendicular angle to the retina. The front of the cornea is supposed to be round but can have slight aberrations even here. The front and back of the lens itself also has significant curvature, with the refractive effects normally being least in the most central portion. The cornea and lens do not typically have to alter perpendicular beams of light as much as the other curvatures must correctly refract the light to the fovea. By having the light pass through the most central portion of these curved surfaces it will tend to filter out astigmatism effects of the more peripheral areas to the greatest degree.
     
  12. Jul 5, 2017 #11

    Ygggdrasil

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    While narrowing the light to the central portion of the cornea would help with limit spherical aberration and improve the shaprness of one's vision, this is probably not the primary effect. Pinholes actually can act to focus light like a lens, and you can use this principle to build a pinhole camera to generate relatively sharp images without any lenses (http://electronics.howstuffworks.com/question131.htm).
     
  13. Jul 5, 2017 #12
    The "pinhole" used for normal vision is not small enough to act as a lens. All it is doing is blocking the line of peripheral sight. An actual lens, such as the lens of the eye, has virtually no correction in its center. The farther you move out from the center, the greater the refraction needed to "correct" the vision. Limiting spherical aberration is the primary effect. Also, a pinhole would still invert the focus of the vision when substituting for a lens, which this beneficial visual effect does not do.
     
  14. Jul 5, 2017 #13

    Ygggdrasil

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    You are right. I guess correcting spherical aberration is the primary effect. Thanks for the clarification.
     
  15. Jul 6, 2017 #14
    Yggg, you were correctly identifying the spherical aberration in your prior post. You did well, my friend!
     
  16. Jul 8, 2017 #15
    I found the lead drawing in the Wikipedia Spherical aberration article very helpful.

    Would this account for the clarity increase with multiple lenses?

    Specifically the Rx - then tinted UV shields - then the clear plastic safety glasses or another UV shield that is clear.

    Additionally. Because of the necessary separations between the UV shield and the clear plastic do these each add a slight bit of magnification to the base Rx?
     
  17. Jul 18, 2017 #16
    I have been looking for open-source optical design software or spreadsheet models that offer calculation basics for glasses, telescopes, microscopes, and similar relatively simple straight through optical systems.

    Any suggestions? Recommendations?

    Thank you.
    Michael
     
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