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). |
