Direction of Floater Movement
Andy Goldfinger
(as much as I can), the floaters seem to drift downward. Now -- the eye
is an inverting optical system. Does this mean that the floaters are
actually moving upward in the vicinity of my retina. If so -- why? Are
they less dense than the fluid which is there?
William Stacy
Yep, the images on the retina are inverted, so if they seem to float down,
they are travelling up your retinas. The vitreous is a complex semi-gel
structure that has signficant and variable moments of inertia within. You
will notice that when you hold your eye very still, this movement will slow
and finally stop (almost), but will move remarkably when you resume normal
eye movement. Gravity is not an issue, since the little structures causing
the shadows have no significant difference in density or mass than the
surrounding vitreous.
w.stacy, o.d.
Mike Tyner
supported by a transparently fine meshwork of fibrous strands scattered
uniformly and attached loosely to the retina. The gel can move against the
retina, or be torn away by trauma, but it keeps scattered cells and debris
embedded in the gel and they all move together, with the whole vitreous "body".
Later the gel becomes more fluid, in places, and you get "lacunae" or pockets of
liquid, interspersed with clumps and strands of collapsed matrix which is more
opaque, and sheets of "vitreous face" which can be quite opaque when turned
sideways. New specks come from either an increase in cellular debris or blood
cells that leak abnormally into the vitreous. Normally it's the former, and the
latter is ruled out in a dilated fundus examination.
There's no circulation per se, and the only other sources of movement are eye
motion and pulse. If you aren't seeing the specks move with your heartbeat,
there's only one force I can think of that would cause movement in the fluid
pockets when the eyes are "still," and that's convection.
In the winter, convection would occur upward on your retina, because the front
of your eye wouldn't be hotter than the back. Unless you're staring into a fire.
-MT
"Andy Goldfinger" <Andy.Go...@jhuapl.edu> wrote in message
news:aslfsh$dpp$1...@houston.jhuapl.edu...
Han Sibot
> > (as much as I can), the floaters seem to drift downward. Now -- the eye
> > is an inverting optical system. Does this mean that the floaters are
> > actually moving upward in the vicinity of my retina. If so -- why? Are
> > they less dense than the fluid which is there?
> Gravity is not an issue, since the little structures causing
> the shadows have no significant difference in density or mass than the
> surrounding vitreous.
In my experience, the vertical motion is real, and I believe that it
is due to gravity.
I was watching my floaters by viewing the sky through a pinhole in
paper, while focusing on a fixed point like the top of a tree
(otherwise, trying to focus on a floater would make him drift away).
After moving my eyes rapidly around, the floaters were swirling around
for a few seconds, then their motion changed and they started raining
down for a few seconds (ok, their physical motion within the eye is
inverted). When repeating this with my head tilted either to the left
or to the right, the floaters still ended up raining down (towards
earth). The fact of vertical motion independent of head tilt is
evidence that the motion of these floaters responds to gravity, not
anatomy.
The whole show somewhat appeared like a toy snow globe. However,
that's a wrong model as William pointed out, because the floaters in
the eye have the same specific density as the surrounding gel. They
don't sink to the bottom. And when the falling motion comes to an end,
the long wrinkled floaters don't deform and flatten out as if they hit
the bottom of a cavity.
So I believe that a gravity effect is visible. The effect itself
remains a mystery. May be both the vitreous and the retina/sclera are
briefly distorted by the muscle action, and they gradually relax at
different speeds. That way the floaters aren't drifting relative to
the surrounding vitreous, they just demonstrate the deformation.
Dan Sontup
> In my experience, the vertical motion is real, and I believe that it
> is due to gravity.
I've had floaters for over sixty years. They move in all
directions, depending on my eye movemments, especically when
reading. They seem to remain more or less stationary if I
concentrate on looking at one point, although there may be a
slight downward movement. If you have the capability of standing
on your head for a while (I'm not trying to be funny!), you might
be able to see if the movement of the floaters is affected in any
meaningful way.
Dan
Jim Lawton
>After moving my eyes rapidly around, the floaters were swirling around
>for a few seconds, then their motion changed and they started raining
>down for a few seconds (ok, their physical motion within the eye is
>inverted).
So they are actually *rising* when they appear to be falling. Certainly I can
confirm that things seen inside the eye are inverted. When I had gas in my eye
following RD surgery, the fluid surface was at the top of my field of view, and
gradually "descended" as the eye refilled with fluid.
Han Sibot
> I've had floaters for over sixty years. They move in all
> reading...
> If you have the capability of standing
> on your head for a while (I'm not trying to be funny!), you might
> be able to see if the movement of the floaters is affected in any
> meaningful way.
I tried it upside down, and I still see floaters falling down to earth
after moving my eyes rapidly around. Moving my eyes rapidly around is
just a way to "stir things up". Stirring things up is just my
subjective expression, it seems to contradict the idea that the
vitreous is really a gel that doesn't flow. However, if I make slow
eye motions instead, I see floaters that move in the same direction as
the eye. That probably corresponds to what you see.
Curiously, the displacement (visual angle) of the floaters is always
smaller than the eye motion, even when waiting for a long time. Hence,
if the eye motion continues in the same direction, those floaters are
lagging behind and they disappear from the field of view.
Don't you see floaters raining down after rapidly moving your eyes
around in several directions? Raising the eye from looking deep down
to looking up is most effective for me.
Han Sibot
news:3e16bd26...@news.cable.ntlworld.com...
> confirm that things seen inside the eye are inverted. When I had gas in my
eye
> following RD surgery, the fluid surface was at the top of my field of
view, and
> gradually "descended" as the eye refilled with fluid.
Interesting! I should keep in mind that swimming goggles and a snorkel may
be useful after RD surgery :-)
I did some new observations with the pinhole, this time with a red LED close
to the pinhole as light source, instead of the sky. The higher brightness of
the LED allowed the use of a smaller pinhole. That implies higher
resolution, and more floaters became visible. The observations are
interesting because they seem to reflect a circulation in the vitreous.
In the "raining-down phase" after vigorous eye motions I noticed that the
conspicuous floaters that were visually moving down, behaved like an
integral flow layer. It contained floaters of approximately identical speed
and identical size (thickness, in the case of strands). But in addition
there was a second layer with floaters, which was flowing in the opposite
direction. Compared to the first layer, the size and the speed of the
floaters curiously appeared to be magnified (about 3x). The floaters of this
layer were less bright in the previous observations with the larger pinhole,
hence they had not been noticed.
Presumably the floater images on the retina are diffraction patterns of
relatively small dots and thin strands. Hence, the different magnification
of their image on the retina means that the second layer is further away
from the retina, while the physical speed of both layers in the vitreous is
really equal. The opposite direction probably means that the two layers are
two sides of a circulation.
I mention this idea because more people have reported that they sometimes
see floaters moving in opposite directions. Did you ever notice such
floaters?
Jim Lawton
>
>Interesting! I should keep in mind that swimming goggles and a snorkel may
>be useful after RD surgery :-)
>
You don't know how right you are - it did sometimes feel as though I'd got a
fish-tank pressed to my eye...
>I did some new observations with the pinhole, this time with a red LED close
>to the pinhole as light source, instead of the sky. The higher brightness of
>the LED allowed the use of a smaller pinhole. That implies higher
>resolution, and more floaters became visible. The observations are
>interesting because they seem to reflect a circulation in the vitreous.
>
Your great great granddad wasn't Benjamin Franklin was he :0)
>In the "raining-down phase" after vigorous eye motions I noticed that the
>conspicuous floaters that were visually moving down, behaved like an
>integral flow layer. It contained floaters of approximately identical speed
>and identical size (thickness, in the case of strands). But in addition
>there was a second layer with floaters, which was flowing in the opposite
>direction. Compared to the first layer, the size and the speed of the
>floaters curiously appeared to be magnified (about 3x). The floaters of this
>layer were less bright in the previous observations with the larger pinhole,
>hence they had not been noticed.
>
>Presumably the floater images on the retina are diffraction patterns of
>relatively small dots and thin strands. Hence, the different magnification
>of their image on the retina means that the second layer is further away
>from the retina, while the physical speed of both layers in the vitreous is
>really equal. The opposite direction probably means that the two layers are
>two sides of a circulation.
>
>I mention this idea because more people have reported that they sometimes
>see floaters moving in opposite directions. Did you ever notice such
>floaters?
>
Well one of the benefits of RD surgery is that you get the vitreous removed, so
that eye is near enough floater-free.
As to the idea that the floaters are circulating or whatever, I think that you
are absolutely right. Maybe the closest you get is the contents of a fresh egg.
If you take an egg, spin it on the table, then stop it for a moment, then let
go, it will start to spin again, because the contents were in motion. The same
thing happens when you move your eye.
>
>
Han Sibot
you
> are absolutely right. Maybe the closest you get is the contents of a fresh
egg.
> If you take an egg, spin it on the table, then stop it for a moment, then
let
> go, it will start to spin again, because the contents were in motion. The
same
> thing happens when you move your eye.
layer with the sinking floaters never maintains its "central" position, but
always descends to a lowest position at about 20 degrees below the horizon,
while my eye is gazing towards the horizon. Consequently other floaters come
into view when I tilt my head to the left, and others when I tilt my head to
the right, and others when my head is upside down.
This description represents what I see. I'm still wondering why gravity
forces layers with floaters to move up or down. As mentioned before, the
layer with the apparently sinking floaters, close to the retina, is actually
moving upwards. I already mentioned the layer with oppositely moving
floaters near the back of the lens, that closes the circulation. It is
unsatisfactory if that layer were composed of vitreous gel: as the specific
densities are identical everywhere in the circulation, there is no reason
for gravitation to generate a circulation. It is an option, however, that
the eye lens is the main component of that layer. Does anyone know if the
eye lens has a higher specific density than the vitreous? That would explain
why gravitation generates a circulation, as well as its direction.