Human eyes in more details


the human eye and vision the following
points will convert in this video. 1 the structure of the eye cornea
lens focusing cornea accommodation structure
of the eye the iris is roughly equivalent to the diaphragm in a camera
the cornea and the lens are both lens like objects and the retina is where the
image is recorded similar to a CCD sensor or film
structure of the eye iris the iris is similar to the diaphragm in a camera
your iris widens and dim light and narrows in bright light the f-number of
your I varies from F slash to large opening to F slash 8 small opening
compare this to the range of an average camera line of / 2.8 to F / 22 structure
of the eye iris with a range of only F / 2 F / 8 your iris can only reduce the
light coming into your eye by a factor of 20 the range of intensities that your
eye can respond to is a factor of 13 power on 10 the main function of the
iris is not to control the intensity of light coming into your eye main
functions the virus reduce aberrations sharpen image
structure of the eye cornea and lens there are two lenses in your eye the
cornea and the islands the cornea the front surface of the eye does most of
the focusing in your eye the eye lens provides adjustable file structure of
the eye cornea and lens this is because the cornea air surface has a large
change in the index of refraction so light bends a lot the power of the
cornea lens is 43 diopters focal length two point three centimeters the islands
is surrounded by the humors which have a VIX of refraction as the lens itself how
your eye focuses the eye lens is a fixed unchanging distance x1 from the retina
at the back of the eyeball where the images create the islands accomodation
the islands changes its focal length by changing its shape ligaments pull on the
lens to change the amount of islands accommodation muscles contract ligaments
relax more bulge more bending power shorter focal length
muscles relax ligaments contract less bulge less bending power how your eye
lens focuses your eye lens has a small depth of field you can’t see something
close and far with both objects in focus at the same time hold out your thumb
about a foot away from your eye then alternately focus on thumb and me right
above your thumb note that you cannot sulcus at the same time you focus on one
or the other by changing the Bulge of your eyelid you can understand
accommodation by this image given here structure of the eye retina the retina
is the sensor or film of your eye it’s layers do three things
provide blood and nutrients choroid absorb light and convert to an
electrical signal photoreceptors this image shows the inner structure of the
retina photoreceptors rods and cones and converted to an electrical signal by
the photoreceptors in the retina there are two main kinds of receptors rods and
cones this is a false color image rods and cones are not actually differ to
receptors cones cones are responsible for our fine detailed and color vision
cones are clustered near the center of your retina called the fovea there are
five million cones and photoreceptors rods rods are responsible for low light
and peripheral vision they are present everywhere in the retina except the
fovea there are 125 million rods in the rods and cones because of their
different functions rods and cones are present in varying densities in the
retina the blind spot is due to the connection of the optic nerve light
sensitivity remember we talked about rods and cones cones
two bright light fought Opik conditions densely-packed in the fovea only a few
cones per nerve fiber rods sensitive to low light scott Opik
conditions retina ten hundreds of rods per nerve fiber
think of this as many many drops falling into the same pipe one drop can’t be
detected but many drops generate some water flow that can be measured dark
adaption even within the cone and rod system your retina adjusts its
sensitivity in response to the overall light level when you walk into a dark
room you can’t see anything but after a few minutes you adapt and can start to
see things when you walk out into the bright sunlight everything is blinding
dark adaptation after about thirty minutes
your eyes are completely dark adapted and can see an amount of light
equivalent to a candle ten miles away dark adaptation is a slow process but
allows us to see in a huge range of light thanks for watching the video
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