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The Eye
Chapter 8
Sclera
• Thick, white tissue that covers the outermost
part of the eyeball
– The “white of the eye”
• Central, anterior portion is clear
Cornea
• Transparent window through which light
enters the eye
Did you know…
•The cornea is the only tissue in
the body that can be
transplanted without the worry
of rejection
•Since no blood vessels can
reach the cornea, it is out
of the reach of the immune
system
Choroid
• Middle coat of the eyeball
• Prevents light from scattering inside the eye
Iris
• Band of muscles that control the size of your
pupil
• Pigment in iris determines the color of your
eyes
Did you know…
•People with blue eyes have the
least amount of pigment in their
iris
•People with brown eyes have
the most pigment in their iris
Pupil
• Opening in the iris that regulates the amount
of light that passes into the eye
– Constricts: close vision & bright light
– Dilates: far vision & dim light
Lens
• Focuses light entering the eye on the retina
• Cataracts:
– Lens gets hard and opaque causing it to not be
able to focus light as well resulting in hazy vision
and eventually blindness
Nearsighted vs. Farsighted
• Lens doesn’t focus light correctly on retina
• Nearsighted (myopia)
– Distance objects appear blurry
– Point of focus before retina
• Farsighted
– Near objects appear blurry
– Point of focus behind retina
Retina
• Innermost layer
• Contains photoreceptor cells that respond to
light
– Rods
– cones
Photoreceptors
• Rods
– Allow us to see gray tones
– Provide for peripheral vision
Did you know…
•Colorblindness is more
frequent in men than
women…it is a sex linked
trait
• Cones
– 3 varieties (red, green, blue)
– Allow us to see colors
– Color blindness: caused by lack of cone type
Optic Nerve
• Photoreceptors transfer message they receive
from light to the optic nerve
• Optic nerve sends message to brain
– Result is vision.
• Blind spot:
– Location where optic nerve leaves eyeball (optic
disk)
– no photoreceptors
Aqueous Humor
• Anterior to the lens
• clear watery fluid
• Helps maintain pressure inside the eye so it
doesn’t collapse inward
• Glaucoma: aqueous humor is blocked from
draining and increases the pressure in the eye
and compresses the retina and optic nerve
Vitreous Humor
• Posterior to the lens
• Gel like
• Helps maintain pressure inside the eye so it
doesn’t collapse inward