Lindsay,

I'm surprised nobody has responded. I've always assumed everyone with
imperfect focus saw those. I see them in both eyes, but one is bigger
than the other. They really do look most like a biological cell under
a microscope. Mine even squirm around slightly, both the outline and
what look like internal structures. I believe that is due to the
varying thickness of the film of tears over my cornea. Blinking or
squinting sloshes the tears around and exaggerates the apparent
movement for awhile.

I can also see them around specular reflections in full daylight. Like
right now there are raindrops on the leaves outside my window, and
each one is surrounded by the characteristic "cell" when the sun hits
it.

I have a bit of diagonal astigmatism, so each of my "cells" is
stretched in one direction, and the directions cross each other. It is
interesting to observe how the amount and direction of the astigmatism
change slightly from hour to hour and day to day. The shape of the
cells also changes if I stare at the same point while moving my head
around - in some directions near the edges of my eye movement range
the cells shrink almost to a point. And of course nearly closing my
eyelids constricts the cells to horizontal strips.

I think the apparent internal structure of the cells is due to
irregularities in my cornea, and particles and viscous globs in the
tears covering it. The internal design stays basically the same, but
constantly  changes slightly and fluidly. I can even watch layers of
tears flow down across the cells like thin frosting down the side of a
cake.

The same pattern that creates the "cells" is detectable in the blur
around everything I see, even in full daylight - but it is much easier
to ignore when there isn't a dark background for it to spread over.

What I find really interesting is what happens when I view points of
light at night through a window screen (easiest to see if the screen
is halfway between the light and my eyes, and the distance is at least
20 feet). The "cell" patterns overlap into a texture that appears to
hang in space like laser speckle, and if I move my head the pattern
appears to move even faster in the opposite direction. That means I'm
a bit myopic - if your focus is perfect, the pattern doesn't move (and
probably isn't visible anyway).

All this is probably trivial, but I find it odd how little we talk
about the internal experiences and artifacts of seeing.

Loren