jlind@xxxxxxxxxxx writes:
<< Anyone steeped in knowledge about the human eye want to comment on
this? Is this the source of it? >>
John,
I have just been rereading "The Eye and the Brain" by Gregory and it has
a color photograph taken with an opthalmoscope showing the retina. The Foveal
area certainly is more yellow but even it has blood vessels and still looks
reddish. The Foveal area is also pretty small at about 1/3 degree of arc.
Seems unlikely to be big enough to cause this, even if it were fully yellow.
An interesting number for the eye is the Total number of photoreceptors
at about 120million. A large number of which are preprocessed by the retinal
nervous tissue so that they only detect gross image features (edges etc) and
movement. The smallest receptors in the foveal area are about 1 micron in
size and with a similar spacing (approx 2 wavelengths of red light). The
foveal area does not have that many receptors even though they are tight
packed.
Mamals and vertebrates have "inside out" eyes with blood vessels and
nervous tissue above the photo receptors but cephalapods have the eye "the
right way round", so go take some pictures of cephalapods for no red eye
effects!
Human eyes are interesting in that the stereo vision aspects are
highly developed, but in most animals including some animals that have both
eyes looking forward (not that common) the stereo aspects are not well
developed. This is true for cats for example which have much higher
sensitivity eyes. Some birds and primates seem to have the most highly
developed stereo/depth perception abilities. The speculation in primates was
initially they needed good depth perception for swinging from tree to tree
and then used that for developing manual manipulation skills.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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