The retina is
located at the back of the human eye.
The retina may be described as the "screen" on which an image
is formed by light that has passed into the eye via the cornea, aqueous
humour, pupil, lens, then the hyaloid and finally the vitreous
humour before reaching the retina.
The function of the retina is not just to be the screen onto which
an image may be formed (necessary but not sufficient), but also to collect
the information contained in that image and transmit it to the brain
in a suitable form for use by the body.
The retinal "screen" is therefore a light-sensitive structure lining
the interior of the eye. It contains photosensitive cells (called
rods and cones) and their associated nerve fibres that convert the light
they detect into
nerve
impulses
that
are
then
sent onto the brain along
the optic nerve.
The retina has a complex structure that specialist texts describe in
terms of ten layers labelled (from contact with the vitreous
humour,
outwards) as:
_1. _ Membrana
limitans interna.
_2. _ Layer
of nerve-fibers (stratum opticum).
_3. _ Ganglionic
layer, consisting of nerve cells.
_4. _ Inner
molecular,
or plexiform, layer.
_5. _ Inner
nuclear layer, or layer of inner granules.
_6. _ Outer
molecular,
or plexiform, layer.
_7. _ Outer
nuclear layer, or layer of outer granules.
_8. _ Membrana
limitans externa.
_9. _ Jacob's
membrane (layer of rods and cones).
10. _ Pigmentary
layer (tapetum nigrum).
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