The document describes the anatomy and functions of the human eye. It explains that light enters the eye and is focused by the cornea and lens onto the retina. The retina contains light-sensitive cells that convert the image to neural signals sent to the brain via the optic nerve. It also provides details on common eye conditions like cataracts and pink eye, as well as comparisons between human and cow eye anatomy.

1. The Human Eye

2. How do your eyes work?
 The Human eye has the task
of focusing light onto the
retina.
 The retina is a thin layer of
neural cells that lines the
back of the eyeball, it is a
part of the central nervous
system.
 The cornea and lens help to
converge light rays to focus
onto the retina.

3. Anatomy of the Eye
 Choroid - the intermediate layer of the eye
that is located underneath the iris.
 Conjunctiva - the mucous membrane that
lines the inner surface of the eyeball. The
conjunctiva continues over the forepart
(part we see) of the eye.
 Cornea - the clear front window of the eye.
The cornea transmits and focuses light
into the eye.
 Iris - the colored part of the eye. The iris
helps regulate the light that enters the eye.
 Pupil - the dark center in the middle of the
iris. The pupil determines how much light
is let in to the eye. It changes sizes to
accommodate for the amount of light that
is available.
 Lens - the transparent structure inside the
eye that focuses light rays on to the retina.

4. Anatomy of the Eye
 Retina nerve layer that lines the back of the
eye. The retina senses light and creates
impulses that are sent through the optic
nerve to the brain.
 Macula - a small area in the retina that
contains special light sensitive cells. The
macula allows us to see fine details clearly.
 Optic Nerve - the nerve that connects the
eye to the brain. The optic nerve carries
the impulses formed by the retina to the
brain, which interprets them as images.
 Sclera - the thick, tough, white outer
covering of the eyeball.
 Vitreous - the clear, jelly-like substance
that fills the middle of the eye. The vitreous
gives the eyeball its shape.

5. How you see an object
 The light rays enter the eye through the
cornea (transparent front portion of eye to
focus the light rays)
 Then, light rays move through the pupil,
which is surrounded by Iris to keep out
extra light
 Then, light rays move through the
crystalline lens (Clear lens to further focus
the light rays )
 Then, light rays move through the
vitreous humor (clear jelly like substance)
 Then, light rays fall on the retina, which
processes and converts incident light to
neuron signals using special pigments in
rod and cone cells.

6. How you see an object continued
 These neuron signals are transmitted
through the optic nerve,
 Then, the neuron signals move through
the visual pathway - Optic nerve > Optic
Chiasm > Optic Tract > Optic Radiations
> Cortex
 Then, the neuron signals reach the
occipital (visual) cortex and its radiations
for the brain's processing.
 The visual cortex interprets the signals as
images and along with other parts of the
brain, interpret the images to extract
form, meaning, memory and context of
the images.

7. Cataracts
 A cataract is an hardening of the
normally transparent lens that leads
to blurred vision.
 Cataracts form for a variety of
reasons, including long-term
ultraviolet exposure, secondary
effects of diseases such as diabetes,
or simply due to advanced age.
 Surgical Treatment is neccessary

8. Conjunctivitis (Pink Eye)
 An infection of the conjunctiva
(the outer-most layer of the eye
that covers the sclera).
 Conjunctivitis requires medical
attention.
 Easily treated but contagious
though normal contact

9. Coloboma
 A coloboma (also part of the rare Cat eye
syndrome) is a hole in one of the structures of the
eye, such as the eyelid, iris, retina, choroid or optic
disc. The hole is present from birth and can be
caused when a gap called the choroid fissure
between two structures in the eye, which is
present early in development in the uterus, fails to
close up completely before a child is born. The
classical description in medical literature is of a
key-hole shaped defect. A coloboma can occur in
one or both eyes.

10. Eye Disorders
 Keratoconus is a degenerative non-
inflammatory disorder of the eye in which
structural changes within the cornea
cause it to thin and change to a more
cone shape than its normal gradual
curve.
 can cause substantial distortion of vision,
with multiple images, streaking and
sensitivity to light.
 Treatment includes Corneal transplant or
wearing corrective lenses

11. Facts about the Eye
Basic Structures:
 The lens grows layers like an onion. As you get older, the lens becomes less flexible
because the buildup of layers compacts the center of the lens, making it more rigid. When
the lens becomes less flexible, it can’t change shape to focus on things nearby. This is
why people need glasses as they get older.
 The lens does only about 20 percent of our focusing. The cornea does the other 80
percent. The lens changes shape so that you can focus on things that are near and things
that are far away. The ciliary body controls the shape of the lens.
 Cones are one type of photoreceptor cells in the retina. They are responsible for daylight
and color vision.
 Rods are the other type of photoreceptor cells. They respond to dim light.

12. Facts about the Eye continued
Basic Structures continued:
 The fovea is a dimple in the retina where cones are concentrated and vision is most
accurate.
 The aqueous humor is the clear fluid that helps the cornea keep its rounded shape.
 The fat that surrounds the eye is there for a reason. It helps cushion the eye and protect
it from the hard bone of the eye socket.
 The human eye is a slightly asymmetrical (uneven) sphere with an approximate diameter
of 24-25 millimeters. It has a volume of about 6.5 cubic centimeters.
 Each eyeball is held in position in the orbital cavity (the area of your skull where your eyes
fit) by various ligaments, muscles and facial expansions that surround it. The extraocular
muscles move the eyeball in the orbits. When you move our eyes from side to side, your
are using your extraocular muscles.
 The blind spot is the area where the optic nerve leaves the retina. Each eye has a blind
spot where there are no photoreceptor cells.
 The eye has tiny blood vessels that carry blood to the retina.

13. Cow Eyes vs. Human Eyes
 A cow’s cornea has about seven or eight layers of material. We
have three to five layers. The cow needs these extra layers of
protection because it spends so much time grazing close to the
ground, where its eyes could be damaged by sticks or other objects.
 Another difference between the cow’s eye and the human eye is
the shape of the pupil. The cow’s pupil is oval. Our eyes have
round pupils.
 Cows cannot see color, only shapes. Humans can see color
because they have cones in their retinas. Cows do not have these
cones.
 The shiny blue-green tapetum helps the cow see at night. Many other animals have a
tapetum. You may have seen their eyes glow when your car’s headlights flash on them.
The tapetum helps animals see at night by reflecting the light entering the eye back at the
retina a second time.
 The iris is the part of the eye that gives us brown, blue or green eyes. Human eyes can be
different colors, but all cows have brown eyes.
 Vision Problems

14. Cow Eyes vs. Human Eyes continued
 Nearsightedness is called myopia. Myopia is a refractive error and
means that a person sees objects that are close by more clearly
that those that are far away. Myopia is inherited and is often
discovered in children between the ages of 8 and 12. Eyeglasses
or contacts can correct the problem.
 Farsightedness is called hyperopia. Hyperopia causes near
objects to be blurred and distant objects to appear clear. Like
myopia, hyperopia is usually inherited and can be corrected with
eyeglasses or contact lenses.
 Astigmatism occurs when the corneal curve is steeper in one
direction than in the other, like the back of a spoon. This causes
light rays to focus at multiple points on the retina, distorting both
near and far vision. Almost everyone has some degree of
astigmatism, but vision is not noticeably affected unless the
uneven curvature is severe. Many people have astigmatism in
combination with myopia or hyperopia.

15. Cow Eye Dissection Step by Step
Step 1:
Examine the outside of the eye. See how many parts of the
eye you can identify. You should be able to find the white
(sclera) and the clear covering over the front of the eye
(cornea). You should also be able to identify the fat and
muscle surrounding the eye.
Step 2:
Make the first incision where the sclera meets the cornea. Cut
until the aqueous humor is released. The aqueous humor is
a clear fluid that helps the cornea keep its rounded shape.
Step 3:
Rotate the eye and cut around the cornea. Be careful not to
cut too deep or you may cut the lens. As the cornea starts to
cut free, hold the cornea in the center and make the last cuts
around it.

16. Cow Eye Dissection Step by Step
Step 4:
Once you have removed the cornea, place it on the board
(or cutting surface) and cut it with your scalpel or razor.
Step 5:
With the cornea removed, the next step is to pull out the iris.
Place one finger in the center of the eye. Find the iris and
pull it back. It should come out in one piece.
Step 6:
It can be a bit tricky to remove the lens with the vitreous
humor attached. It works best if you cut slits in the sclera.
Be careful not to cut the lens.

17. Cow Eye Dissection continued
Step 7:
After enough incisions have been made in the sclera,
you should be able to remove the lens. Sometimes
the vitreous humor will be removed along with the lens.
Step 8:
Hold up the lens and look through it. If the lens is too
slippery, pat it dry and try again.
Step 9:
With the vitreous humor now removed, you should be
able to turn the eye inside out.

18. Cow Eye Dissection continued
Step 10:
The thin tissue on the back of the eye is the retina. Find the spot where
the retina is attached. The shiny blue-green material is the tapetum.
Step 11:
Find the spot where all the retina’s nerves collect. It is called the blind
spot. This is where all the nerves go out the back of the eye, forming the
optic nerve.
Step 12:
Return your attention to the outside of the eye. Locate the optic nerve.
To see the separate fibers that make up the optic nerve, pinch the nerve
with a pair of scissors or with your fingers.
Step 13:
Once the dissection is complete, properly dispose of the remains and
wash your hands.