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Seeing Spots
This week's experiment is something that I first
noticed as a child. You may have noticed it yourself. Part of the fun of
science is taking something that you notice yourself and finding out what causes
it.
For this experiment, you will need:
If you don't have a blue sky available, you can try
using a sheet of blue paper. Other colors will work, but blue seems to work
better. It works best of all with a blue sky, preferably while you are digging
for fossils, bird watching, or other similar activities.
Stare at the blue sky and let your eyes go a little out
of focus. As you look at the sky, you will notice that you begin see tiny spots
moving around.
As you watch them, you should notice that they seem to
be following pathways instead of just moving around randomly. The more you
watch them, the easier it is to see these pathways and the patterns of their
movement.
What are you actually seeing? Are these UFO's? Some
strange kind of bird migrations? No, the spots you are seeing are actually
inside your eyes. You are seeing white blood cells moving through the blood
vessels at the back of your eye. At the back of your eye is your retina. This
contains the light sensitive cells that let you see. Tiny blood vessels bring
nutrients and oxygen to the cells of the retina. Normally you don't see these
vessels, but when you are staring at the blue sky there is nothing else for your
eyes to focus on. You don't see the smaller red blood cells, but the white
cells are large enough for you to see. The pathways that they are following are
the tiny vessels that carry your blood.
Some medical researchers are using this as a way to do
quick, easy white cell counts for patients with immune system problems.
Patients can learn to compare the number of spots that they see with charts, to
estimate their white cell count. This helps them avoid taking frequent blood
samples. As someone that has a phobia about needles, this sounds like a
wonderful idea to me.
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