Foveola Speckle Pattern?
Han Sibot
of light through my eyelid, with eyes closed. First I used a pentorch, then
a bright red LED. As expected, this results in diffuse illumination of the
whole retina. The black blood vessel shadows show up nicely against that
background. While using the LED I noticed that the central disk of the
foveola (1.5 degrees of visual angle in diameter) had a different
appearance, granular like a speckle pattern (like a rough surface
illuminated by laser), instead of the smooth background. It seemed to be a
true speckle pattern because the pattern was sharp although the eye lens was
bypassed. The speckle character was confirmed by moving the LED over the
eyelid: the granular pattern moves relative to the blood vessel shadows. If
the LED moves to the left, the granular pattern moves to the right, relative
to the blood vessels.
Does anyone have an idea why this speckle pattern appears in the foveola?
William Stacy
No, unless you're illuminating with a laser, there should be no speckle pattern
in the fovea, because the granularity of the receptors in this area is too fine
to resolved. You are getting some other artifact.
w.stacy, o.d.
Han Sibot
> No, unless you're illuminating with a laser,
I thought lightwaves made by stimulated emission are not fundamentally
different. The reflection spectrum of the LED in a cd gives me the
impression that its bandwidth is about 10%. That seems to be narrow
enough for the interference minima and maxima of a speckle pattern,
although the minima won't be perfectly black.
> there should be no speckle pattern in the fovea, because the
> granularity of the receptors in this area is too fine
> to be resolved. You are getting some other artifact.
On the other hand, the fovea is definitely able to observe speckle
patterns created by an irregular surface elsewhere. The sclera might
be the source of a speckle pattern.