Science Notes by Ahmet Arduc - Seeing Inside Your Eye
by Ahmet Arduc – www.ahmath.com
PARTS OF THE EYE
Blind spot: small area of the retina where the optic nerve leaves the eye: any image
falling here will not be seen
Cornea: transparent tissue covering the front of the eye: does not have blood vessels;
does have nerves
Iris: circular band of muscles that controls the size of the pupil. The pigmentation of
the iris gives "color" to the eye. Blue eyes have the least amount of pigment; brown eyes
have the most.
Lens: transparent tissue that bends light passing through the eye: to focus light, the
lens can change shape
Optic nerve: bundle of over one million axons from ganglion cells that carry visual
signals from the eye to the brain
Pupil: hole in the center of the eye where light passes through
Retina: layer of tissue on the back portion of the eye that contains cells responsive to
Sclera: tough, white outer covering of the eyeball; extraocular muscles attach here to
move the eye.
As an object gets further away less of its light will reach your eye. The
image takes up less space on your retina (the light-sensitive tissue at the
back of your eye), making the image smaller. This makes details of the
image harder to see.
The Blind Spot
Each of your eyes has an area on the retina which does not
have any receptors. This is because this area is occupied by the
optic nerve. So any image which falls on these receptors will
not be seen.
To see this, close your left eye and look at the + in the image
below. Move your right eye in closer to the + and then move
farther away. At some point, the circle on the right will
disappear. That is because it is in your blind spot.
You don’t notice your blind spot though, because
your brain fills in the area with an image based on
what is around it. This is a cognitive illusion. To see
this, close your left eye again and look at the + in
the picture below. Move closer and further away
until the red X disappears. At just the right spot, it
will look like the line has filled in where the X was.