How the retina works

MZ zarellam at twcnyremove.rr.comspam
Wed Jul 21 18:47:48 EST 2004

> The blood column is essentially opaque, and casts a distinct shadow. If it
> were a simple camera, the film would have a superimposed blood-vessel
> pattern on every picture. Instead, the retina "filters out" static images,
> those without moving edges. If you wiggle a penlight against the sclera
> cause the shadows to move, the vessels become dramatically visible - a
> phenomenon called Purkinje's tree.

I was under the impression that the brain compensated for the vascular
shadows on the retina.  Hence the "representation", so to speak, of the
vessels in cortex (eg. Horton's recent "angioscotoma" papers).

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