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Natural Science Forum / Physics / Research / July 2008Seeing fluid on the surface of your eye - how does this work?
If I take 3 playing cards and arrange them in front of my eye, so that a very small triangular aperture is created by the cards, and I adjust this aperture so that it is sufficiently small for the brightness of the light to be somewhat diminished, I notice I am able to observe the droplets of fluid on the surface of my eye (especially when I blink) which I ordinarily can't see. What am I doing to the light, and why can I see the fluid? Thank you. On 9 Jul, 07:15, daniwe...@gmail.com wrote: > If I take 3 playing cards and arrange them in front of my eye, so that > a very small triangular aperture is created by the cards, and I adjust [quoted text clipped - 3 lines] > which I ordinarily can't see. What am I doing to the light, and why > can I see the fluid? Thank you. I think you have a pinhole camera. - Ian Parker On Jul 9, 2:15 am, daniwe...@gmail.com wrote: > If I take 3 playing cards and arrange them in front of my eye, so that > a very small triangular aperture is created by the cards, and I adjust [quoted text clipped - 3 lines] > which I ordinarily can't see. What am I doing to the light, and why > can I see the fluid? Thank you. My guess is that you’re diminishing the ambient light enough that only the area very close to the surface of your eye is illuminated. You’ve filtered out the light from all of the other things you normally look at so as to make this possible. J Leonard > On Jul 9, 2:15 am, daniwe...@gmail.com wrote: > > If I take 3 playing cards and arrange them in front of my eye, so that [quoted text clipped - 9 lines] > filtered out the light from all of the other things you normally look > at so as to make this possible. The cornea's surface has at least four layers going outward: conjunctiva, mucin, tears, meibomian. Going inward you have the front side of the bag, the front and back of the lens, and the back of the bag. Then you have shed tissue ("floaters") near the retina. It's all about signal-to-noiser ratio and selective signal recognition. -- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 On Jul 8, 11:15=A0pm, daniwe...@gmail.com wrote: > If I take 3 playing cards and arrange them in front of my eye, so that > a very small triangular aperture is created by the cards, and I adjust [quoted text clipped - 3 lines] > which I ordinarily can't see. What am I doing to the light, and why > can I see the fluid? Thank you. I used to think of the exact same question. I have bad eyes so I just needed to take off my glasses and look at a point light source to see interference pattern from the liquid drops on the eye. Blinking the eye lid kind of refreshed the surface. It was a question from me about the whole meaning to interference as related to the objective study of cause to the pattern. I would try to distinguish the interference between two such liquid drops patterns. A light to dark overlay occurs when two patterns resolve. I was simply curious. And in the end a common interference pattern was all I could attribute to this event. Objective eye effect as a mysterious event of the eye was found to NOT exist. A patttern self effect proved the common event of interference. A source of light and the eye as the sensor was all it means. No mysterious eye effect is seen. > On Jul 8, 11:15pm, daniwe...@gmail.com wrote: > [quoted text clipped - 22 lines] > the eye as the sensor was all it means. No mysterious eye effect is > seen. he acid test for physical/geometrical optics is the predence of COLORED fringes. I have repeated the experiment myself. I do indeed see patterns but they are not colored. Hence I believe the effect to be purely geometrical. - Ian Parker On Jul 11, 11:01 am, Douglas Eagleson <eaglesondoug...@yahoo.com> wrote: > On Jul 8, 11:15=A0pm, daniwe...@gmail.com wrote: > [quoted text clipped - 22 lines] > the eye as the sensor was all it means. No mysterious eye effect is > seen. I don't know if we are talking about the same effect, but I see (and many other people I know see) small dark spots and circular interference patterns when I look to a clear blue sky. The explanation someone gave me (at a science museum) was that those spots, and the interference associated to them, are blood cells at the surface of the eye. To check if this is true you have to look for your heart pulse and compare the beating to the movement of the spots. On Jul 8, 11:15 pm, daniwe...@gmail.com wrote: > ... I notice I am able to observe the > droplets of fluid on the surface of my eye (especially when I blink) > which I ordinarily can't see. What am I doing to the light, and why > can I see the fluid? Thank you. You are assuming this is fluid on the surface of your eye: It can't be, because the absorbance of anything in corneal fluids (barring some sort of disease) is too low. What you are seeing is dead blood cells and other detritus in the vitreous humor, casting shadows right against your retina. The analogy to a pinhole camera is correct: The small hole allows the point-spread function to be very narrow, allowing high- resolution vision of this stuff. You also may be able to see strands of broken fibers which used to anchor the vitreous humor to the eyeball. As you age, your vitreous humor turns slowly from firm jelly to watery liquid, starting near the retina. It fragments and detaches from the retina. So, the stuff you see will become more heavily populated ("dirtier") as you age. This won't interfere with vision, because it in not in the retinal object plane. But, refractive index differences in the vitreous humor may make your vision intermittently blurry as you age; this resembles the effect of mucous or other substances in the tears but is not. On Jul 13, 5:42 pm, "jw...@BasicISP.net" <jw...@basicisp.net> wrote: > On Jul 8, 11:15 pm, daniwe...@gmail.com wrote: > [quoted text clipped - 30 lines] > resembles > the effect of mucous or other substances in the tears but is not. Thanks to everyone for your thoughtful replies! I believe I am certainly seeing droplets of fluid on the surface of my eye for the following reasons: 1. Blinking permanently changes their number, size, shape and position. 2. If I squint, I am able to "corral" them together. When my head is positioned vertically, relative to the ground, the droplets seem to drift chiefly downward (and slightly sideways at times) after I blink. When I position my head sideways, the droplets seem to describe a curved path after I blink, initially fast toward my lower eyelid, and then slower, curving away towards the ground. At no time do they seem to drift up, away from the ground. I think their movement is being influenced both by gravity and by surface tension and/or other fluid mechanical behaviors, which, however, I have no technical knowledge of. But it seems clear these are tear droplets, rather than floaters, which, being inside the eye, would not be so influenced and modified by blinking. - Dan Hi. You can't tell tears from floaters by anything you so far have described, because the eye moves when you blink, and you don't know whether the objects you see are more or less dense than the fluid supporting them. I have seen floaters, and I can't tell them from something on my cornea by any simple experiment. However, you can do a direct test of the tear hypothesis by taking a piece of transparent plastic (Saran wrap) or some other thin, transparent sheet, making a tiny cut or other mark on it, wetting one side with saline solution (in case you accidnetally touch your eye), and putting it very near your cornea while you do the card trick. You could suspend your film on a spectacle frame, for example. Put the cards beyond the film. If you see the mark you made, then it is POSSIBLE you might be seeing something on your cornea. Also, if you can see stuff in your tears with the cards, you should be able to see the same stuff by looking in a good mirror with a magnifying glass and a bright light. If there are blood cells, specks of solid mucous, pigmented protozoa, or anything else highly absorbant in your tear film, you should visit an ophthalmologist, because this would be an indication of a possible injury or disease condition. Keep in mind that a pinhole light source has no magnification, so something 2 cm from your retina (viz., on your cornea) would have to be quite big, a mm or so, for you to see the silhouette image of it. On the other hand, something right against your retina would be so close that it would span several retinal photoreceptors and thus have a pinhole image with easily visible detail. Touching a little on the physics of this problem, an inverse distance law for resolution of detail holds for an object illuminated by a pinhole light source, just as it holds for any other source. daniwe...@gmail.com wrote: > On Jul 13, 5:42�pm, "jw...@BasicISP.net" <jw...@basicisp.net> wrote: > > On Jul 8, 11:15�pm, daniwe...@gmail.com wrote: [quoted text clipped - 55 lines] > > - Dan Thank you for your thoughts and suggestions. Your idea to do an additional experiment is good, but the one you suggest would again produce results observable only to myself, and I am already sure these are tears I'm seeing. I am familiar with floaters, and these droplets behave entirely differently, and are directly affected by blinking, while floaters are not. I believe my previous comments show that, assuming my ability to observe and report is reliable (I assert this is true!) the phenomena I am observing are clearly identifiable as tear droplets, and distinguishable from any phenomenon originating inside the eye. In order for an experiment to be useful in convincing a skeptical other, the results would have to be observable to that other. The experiment would also have to be designed to duplicate the circumstances of the original observation as closely as possible. Since I am myopic, perhaps my setup with the cards should be duplicated by a number of other myopic individuals, and their observations recorded. There would be other factors which also would have to be considered, such as lighting conditions, etc. However, I don't think I want to become involved in setting up such a multi- person study at the present time. An alternative might be to make a setup which works in a way similar to a human eye, substituting a CCD detector for the biological retina, and recording the result as a digital image, but I'm not going to go that far right now. Thank you again for your very thoughtful suggestions. - Dan > Hi. > [quoted text clipped - 39 lines] > daniwe...@gmail.com wrote: > > On Jul 13, 5:42=EF=BF=BDpm, "jw...@BasicISP.net" <jw...@basicisp.net> w= rote: > > > On Jul 8, 11:15=EF=BF=BDpm, daniwe...@gmail.com wrote: > > > > > > > ... I notice I am able to observe the > > > > droplets of fluid on the surface of my eye (especially when I blink= ) > > > > which I ordinarily can't see. What am I doing to the light, and why > > > > can I see the fluid? Thank you. > > > > > > You are assuming this is fluid on the surface of your eye: =EF=BF=BDI= t can't > > > be, because the absorbance of anything in corneal fluids (barring > > > some sort of disease) is too low. =EF=BF=BD What you are seeing is de= ad blood > > > cells > > > and other detritus in the vitreous humor, casting shadows right > > > against > > > your retina. =EF=BF=BD The analogy to a pinhole camera is correct: = =EF=BF=BDThe small > > > hole > > > allows the point-spread function to be very narrow, allowing high- [quoted text clipped - 4 lines] > > > anchor the > > > vitreous humor to the eyeball. =EF=BF=BD As you age, your vitreous hu= mor turns > > > slowly > > > from firm jelly to watery liquid, starting near the retina. =EF=BF=BD= It > > > fragments and > > > detaches from the retina. =EF=BF=BDSo, the stuff you see will become = more > > > heavily > > > populated ("dirtier") as you age. =EF=BF=BD This won't interfere with= vision, > > > because it > > > in not in the retinal object plane. =EF=BF=BD But, refractive index [quoted text clipped - 26 lines] > > > > - Dan |
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