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Medical Forum / General / Vision / October 2008Question about color vision
Hi all, I'm not sure if this is the group to ask but I hope that you will point me in the correct direction if it is not. Years ago I noticed that while wearing my 2.75 reading glasses I can see the world clearly but could not focus on the numbers of my blue led alarm clock. I have no problems with focus on my wife's red led alarm clock. When I take off my glasses I can see the numbers on my blue led alarm clock clearly (after a little focus) but can not see the rest of the world clearly. I tested my self on some of the online color vision tests and it seems like I do NOT have any color blindness. I have used both dime store reading glasses and the high quality ones from my local eye doctor with expensive coatings with the same issue. My doctor didn't know what would cause this issue. Time to find a new doctor? This is not a major issue to me but I was simply wondering why this is so. I have some theories but I would like to know if anyone has any real world explanation as to why this happens. If it helps, I'm almost 40 and can no longer read small print clearly at night without a 60-75 watt light bulb (bummer, I remember reading small print in the dark with no light bulb or glasses) and have a slight stigmatism. Thanks, Chris > Hi all, > [quoted text clipped - 27 lines] > > Chris P.S. I just remembered this, I am nearly blind in one eye (lazy muscle is what I was told, eye is good but the optic nerve is defective) and can only make out faint shapes in that eye. If you are born like this then you grow used to it and don't think about it much. Chris > Years ago I noticed that while wearing my 2.75 reading glasses I can see > the world clearly but could not focus on the numbers of my blue led alarm [quoted text clipped - 3 lines] > clock clearly (after a little focus) but can not see the rest of the world > clearly. Optical properties are different for different colors. Refractive index tables usually assume yellow light, in the middle of the spectrum. Real-world examples are most evident when you compare the extremes of the visible spectrum, eg red and blue. Blue light bends more than red. That means blue things focus closer and red things focus further away. Take your glasses off and it's easier to focus a close blue object than any other color. The difference in behavior across the visible spectrum is called chromatic dispersion. The difference in focal lengths is called the chromatic interval. In the right circumstances, the chromatic interval can be several feet. The chromatic interval can be used to fine-tune spectacle prescriptions. It also causes visual confusion ("vibration") when you print orange or pink letters on a blue background. -MT > Hi all, > [quoted text clipped - 26 lines] > > Chris I think that you are seeing the effects of chromatic aberration. The natural eye also has chromatic aberration, but your brain has accommodated to this by suitable processing of the color receptors (cones). Wearing glasses introduces new aberration which the brain has not been trained to process correctly. Use of this effect was made during the heyday of psychedelics. Posters in red and blue appeared to not be flat but in relief. I am not a vision professional. My comments are based upon some biological knowledge and fairly good understanding of optical physics. If you think that you do have a physical problem with your eyes, see an ophthalmologist. Bill  SignaturePrivate Profit; Public Poop! Avoid collateral windfall! >Hi all, > [quoted text clipped - 3 lines] >Years ago I noticed that while wearing my 2.75 reading glasses I can see the >world clearly but could not focus on the numbers of my blue led alarm clock. It's the correct group, and as you've been told already, it's chromatic aberration that's at the core of what you're experiencing. In theory, you could create an incredibly expensive, and incredibly heavy pair of glasses that minimized the problem by using several different types of lens material with different levels of dispersion (it'd look like a couple of miniature telescopes mounted in front of your eyes), but the best you can do in practice is use an extra-low dispersion material for the one lens. I don't know off hand what's available for eyeglass use (likely not fluorite, which would require coatings just to stay intact in the air), but aside from forcing your OD to look up the best materials for a new pair, the more practical solution would be to avoid alarm clocks with blue digits. Signature- Mike Ignore the Python in me to send e-mail. > >Years ago I noticed that while wearing my 2.75 reading glasses I can see the > >world clearly but could not focus on the numbers of my blue led alarm clock. [quoted text clipped - 5 lines] > with different levels of dispersion (it'd look like a couple of miniature > telescopes mounted in front of your eyes) I was wondering about this. Camera lenses can be heavy and expensive, but that's because you want perfect sharpness from edge to edge of the film, and those lenses that are expensive usually are capable of very low light use. Camera lenses that are small are really quite cheap. Since only the macula requires sharpness, I don't see why glasses with multiple elements would be that expensive and stick out a long ways. Perhaps I just haven't thought it through or maybe I don't understand the issues. > I don't know off hand what's available for eyeglass use (likely not fluorite, > which would require coatings just to stay intact in the air), but aside from > forcing your OD to look up the best materials for a new pair, the more > practical solution would be to avoid alarm clocks with blue digits. I agree that you have the practical solution for that small problem. I bought an LED clock with 2" red digits when I couldn't see at night. It still works well even though I can see OK now. However, there are a whole lot of blue things in this world, and sometimes they include numbers and letters, and not always very big. SignatureDan Abel Petaluma, California USA dabel@sonic.net In article <dabel-398FA5.15181219102008@c-61-68-245-199.per.connect.net.au>, > > >Years ago I noticed that while wearing my 2.75 reading glasses I can see > > >the [quoted text clipped - 17 lines] > Perhaps I just haven't thought it through or maybe I don't understand > the issues. In no way are camera lenses "perfect." The design is always a compromise among conflicting desires. Optical performance of an eye can be relatively lax because you turn your eye toward the object being used to obtain best acuity. Off-axis performance is relatively poor. As you turn your eye but not your head, you look through a different region of the spectacle lens. This increases aberration. > > > I don't know off hand what's available for eyeglass use (likely not [quoted text clipped - 10 lines] > However, there are a whole lot of blue things in this world, and > sometimes they include numbers and letters, and not always very big. There never was a guarantee that optometry would get you back to where you were before glasses. In principle, lasik should be able to give you close to theoretical performance considering the fundamental limitation of eye anatomy. That performance, however, will be on-axis only. With glass lenses, the process akin to lasik is called figuring. I am not a vision or health professional. I know little about the nuts and bolts of lasik. Bill SignaturePrivate Profit; Public Poop! Avoid collateral windfall! Thank you all!!! I will now set forth upon a great adventure and learn all I can about chromatic aberration. This leads to another question, would actual glass be better at minimizing this characteristic than a poly lens? Thanks Chris > Thank you all!!! > [quoted text clipped - 7 lines] > > Chris Glass comes in a large number of varieties. Look, for example, at the Schott catalog. Color correction usually uses two different kinds of glass. That makes color correction for spectacles difficult and expensive. Bill SignaturePrivate Profit; Public Poop! Avoid collateral windfall! |
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