Weird optics

October 21, 2006 8:44 PM

Let's say I find a shiny spherical object and under point lighting, I move it very close to my eye. I then focus on the bright spot, but focus at a distance of 1-2 feet until the patterns are in focus. At this point, it looks like a bad microscope. Am I looking at part of my own eye? Is this a documented phenomenon I could read about?
posted by aye to science & nature (19 comments total)

I notice the same thing when I'm not wearing glasses or contacts, and I look at bright point sources of (obviously, unfocused) light.

It -appears- that I'm looking at microbe-sized things as one would see in a microscope. I always assumed these were particles floating on the surface of my eye.

I'd love to know more, though. Thanks for asking this.
posted by odinsdream at 8:46 PM on October 21, 2006

I don't understand what you're perceiving...

I recall getting an eye exam, and the optometrist had me look into something that shined a light into my eye. The light hit the blood vessels in my eyeball, and I was able to see them as sort of faint red lines. (I know that's what they were, because I asked the optometrist at the time.) Is this what you're talking about?
posted by Brian James at 8:59 PM on October 21, 2006

No, I am not seeing blood vessels (those require slightly different lighting conditions). odinsdream has got it though.
posted by aye at 9:05 PM on October 21, 2006

Doctors call them floaters, muscae volitantes (Latin for "fluttering flies"), or, if they're in a prosaic mood, spots. The specks are variously described as particles, soot, spiders, cobwebs, worms, dark streaks, or rings. Just about everybody experiences them, although they're most common in people who are nearsighted.
posted by Krrrlson at 9:16 PM on October 21, 2006

see also
posted by Krrrlson at 9:17 PM on October 21, 2006

I found these out (my eye doc told me these were 'floaters' and possibly remnants/dead-cells of the eye from early stages of development, but it was long ago when he said so) when lying in bed looking at a street lamp with my glasses off (nearsighted). Also note that you can squint your eye and when opening it back up there will be a "line" as if you had just squished together something and left a ridge of whatever it was. Blinking makes the ridge go away.
posted by vanoakenfold at 9:37 PM on October 21, 2006

When I was younger I swore that these were letters of the alphabet, then decided at school that they were diffraction patterns caused by obstruction by a small object (kind of like an inverse Airy Disk).
posted by claudius at 9:51 PM on October 21, 2006 [1 favorite has favorites]

Thank you so very much for asking this. I have wondered about this for years, and recently so as my mom had floaters that signaled her eye was bleeding internally from (yikes) diabetes-related sight issues.

It's good to know what I see is not just me being crazy! The internet's ability to make us realize we're not the only weird ones shows it's face again! :)
posted by plaidrabbit at 9:53 PM on October 21, 2006

I don't think this has much to do with floaters. It's some form of reflection near the eye surface that forms an image which perfectly converges at the retina again (after reflecting off the shiny object). I just can't figure out the ray diagram, but at least odinsdream proved I'm not crazy.
posted by aye at 9:54 PM on October 21, 2006

Just to clarify, when I'm looking past the reflected point, I see intricate and vast cell-like structures and a dark circle with a rather large radius. I can't get to center of that because otherwise I block the light. Everything is in black & white.
posted by aye at 10:01 PM on October 21, 2006

reflection near the eye surface that forms an image which perfectly converges at the retina again... at least odinsdream proved I'm not crazy.

Don't count on it.
posted by jjg at 10:48 PM on October 21, 2006

I know the phenomenon you're talking about (at least I think I do; it's the same as when I look past a glint on my glasses) and I don't think it's related to floaters. I think the image might be the shape of your pupil, or some other aspects of the optical path from the point source to your retina.
posted by hattifattener at 10:51 PM on October 21, 2006

There was a neat little article in Scientific American many years ago that described how you could turn your eye into a microscope using a piece of heavy paper with a pin hole. I can't remember the optics behind it but basically you just face a window or the look up at the sky and place the paper about 6-12 inches in front of your eye and try to focus at a point beyond/through the pinhole.

The article claimed that the small round floaters were most likely stray red blood cells and that you could even see proteins which appeared as long twisty strings. Oh, and the particles/floaters are inside your eye - not on the surface.
posted by shoesfullofdust at 10:51 PM on October 21, 2006

Let's say I find a shiny spherical object and under point lighting, I move it very close to my eye. I then focus on the bright spot, but focus at a distance of 1-2 feet until the patterns are in focus. At this point, it looks like a bad microscope. Am I looking at part of my own eye? Is this a documented phenomenon I could read about?

I'm not quite understanding what you're describing there. Can you tell us what kind of object perhaps?

But similar to others, I am very near-sighted and lights viewed without my glasses are just big blobs. And in these blobs of light, I could as a child, and still can, see floaters and bits and pieces drift by, and squint to push them together, and blink to undo it.

I used to fall asleep at my grandparents' house as a kid doing this with the lights of the smelter across the valley. Yep, they're floaters, and I have a heck of a lot of them now (at 41 years).

I'm looking past the reflected point, I see intricate and vast cell-like structures and a dark circle with a rather large radius. I can't get to center of that because otherwise I block the light. Everything is in black & white

This I have not experienced. I am curious about it, now, but can't visualise (sorry) the conditions under which you've experienced it.
posted by Savannah at 10:59 PM on October 21, 2006

I think I've experienced something like this when I get a drop of water on my glasses and look at a light source. I can see my eyelashes magnified, and if I play around with the focus a bit, I can see some kind of anatomical structure. Hmm, new experiment for tomorrow!
posted by greatgefilte at 11:47 PM on October 21, 2006

Very cool. Thanks for clearing that up for me.
posted by cowbellemoo at 12:17 AM on October 22, 2006

When you have an eye exam, they flash a light in your eye and you can occasionnally have a glimpse of a strange landscape: you are seeing your own retina.
posted by bru at 7:03 AM on October 22, 2006

Aye, if I am visualizing your description properly (probability much less than 1), I think you could be seeing a direct projection of some of the cellular structure of your cornea or your lens onto your retina.

A nearby point source means the primary light rays falling on any object are highly divergent; by reflecting those rays from the surface of a sphere, you are making them markedly more divergent.

Now visualize these extremely divergent rays passing through your cornea. Since they are so divergent, rays passing through a tiny spot on your cornea will cover a much larger area by the time they reach the retina. This means that any tiny effect at the cornea will be greatly magnified at the retina. If, as they pass through the cornea, some of them reflect from cellular junctions, you would, or could see something like a screen door or a fishnet. I don't think, upon consideration, you are seeing cells of the lens; only the cells of the cornea would seem to be close enough to the sphere for the required divergence.

What I do not understand, as I write, is the dark circle.
posted by jamjam at 12:59 PM on October 22, 2006

If you're seeing what looks like a network of blood vessels, you're seeing the moving shadows of the vessels that are actually lying across the surface of your retina.

Basically, they're always there, your brain is designed to filter out anything that remains perfectly still--since they move in perfect unison with your retina, your brain usually ignores them. If you get a bright point source of light very close to your eye, though, and it moves, then the blood vessels' shadows move against your retina, and your brain starts to pick them out.

You can see the effect easily by taking a penlight, closing your eye, and pressing the light gently against your eyelid. If you move the light around in little circles, you'll see a moving pattern of blood vessels jump out into your visual field.
posted by LairBob at 1:10 PM on October 22, 2006