Hi, here something I always been wondering about.
When you focus on a shining object from very close by ( for example, the light reflected off the end of metal pen, from a distance of less then one inch from one eye ) you see tiny bubbles swimming in your vision. What are those?
I have a few guesses, but I won’t say them yet, so to not bias your answares… 
thanks,
oded.
Lessee - IIRC, they’re what’s left of fetal blood vessels that dissolve inside the eye during maturation. If we’re thinking of the same thing.
I always call 'em floaters. They’re the remnants of some artery you had in your eye when you were a fetus. The artery dissolves and the cells remain. Then again, they could be parasites.
According to my favorite reference on oddball physics, “Th Flying Circus of Physics (with answers” byJearl D. Walker:
“The eye floaters are the diffraction patterns of light passing just in front of the fovea on the retina.” (p. 279, entry 5.96) Among the cited references are H. von Helmholtz’ “Physiological Optics” (still ard to beat after over a century in print) and “Floaters in the Eye”, an article in Scientific American for June 1962, p. 119.
Ok, so they are either remains of arteries or light defractions. but my guess is that they are grains of dust floating on the eye.
what do you say?
Cal, there’s no way your source is correct. Heck, the floaters don’t even look like diffraction patterns!
Here’s what medlineplus.adam.com says:
The link is here: http://medlineplus.adam.com/ency/article/002085.htm
Once again, Cecil has pondered this query http://www.straightdope.com/classics/a2_311.html
Eye bubbles:
That’s what they are. Microscopic bubbles. If you squint you can see that they resemble – don’t gross out – bubbles in spit. I’m not sure if they are in the lubricating fluid on the eye, which is thin (tears), or the thicker fluid behind the Cornea. They are not in the real thick jell within the eye.
They do resemble microbes as seen under a microscope.
I see them when I take off my glasses and look at a distant light at night. They clearly move around a bit and it does seem that blinking changes them, so it appears that they are on the surface of the eye rather than inside. I think that floaters can be seen in normal light when you have your eyes in normal focus. Also, I’ve seen these splotches (which do indeed look like microbes under a microscope) since I was quite young. They don’t look remotely like spiderwebs. I don’t think these are the same thing as floaters.
Unless in is huge, you can’t see any type of stuff (dust, tear film) on your cornea or the surface of your eye. Anything actually obscuring your visual field that you can nearly focus on needs to be near your retina. This is just a function of the way the light converges.
For instance, you may not even know that your contacts have given you a corneal abrasion (besides that it might hurt). If you can see a fuzzy spot in your vision, and it is your cornea, you have a lot more damage than an abrasion (more like an ulcer or something).
I think that what oded and I see is not something inside the eye, nor an abrasion on the surface of the eye, but just the liquid on the surface of the eye. These are not floaters, because they look spherical, not thread-like, and they change when I blink. They are not abrasions because I’ve been seeing them since I was quite young, and I’ve had my eyes examined many times since then. To see them, I think you need to be nearsighted. At night, take off your glasses and look at a distant light that’s bright enough to produce a disk. What I always see in these circumstances is (as Skribbler wrote) small bubbles swimming across a disk, just like looking at microbes under a microscope.
Yes, I see them just like Wendell does. I am near sighted, but I could see them when I was very young, before I was near sighted. The trick is to squint. that something I didn’t mention in my description. squint at a shining object from close by and you will see tiny circles. I never saw threads.
When I was a child I belived that they are jerms that only I can see without a microscope, because of my super-human sight.
BTW, squinting bends the corona, so it might really be related to near sightedness.
still, I do belive the explanetion that they are cellular debree.
When I get tired, I see them as shadows which travel across my vision when looking into the white background of the computer screen when I work.
Squinting produces threads, rods, clusters of assorted ‘bubbles’ in clumps or even lines.
Derleth:
That “come and go without treatment” thing is puzzling to me, since it implies the floaters inside the eye are temporary.
But I’ve had the same ones all my life, since I was a small boy! I know this because their shapes are highly eccentric and asymmetrical. If they’d gone away and been replaced by new ones over time, wouldn’t they have different shapes? But if they’re cellular debris left over from the fetal stage, I don’t see where they could go, or where the new debris would come from.
Derleth:
Please check the sources I cite (especialy the sketches in Walker). They do indeed look as you describe. Such things can, indeed, be diffraction patterns – not all diffraction effects look like an Airy pattern, especially when the detection ystem might not have the resolution to see fine details. See some of the other examples in Walker’s book. Heck – see a rainbow. Rainbows are really diffractive phenomena, not strictly refractive phenomena. See any good book on rainbows.