Eye Dissection
Materials
Sheep eye
Lab Apron
Tweezers
Latex/Vinyl Gloves
Dissecting probe
Dissecting tray
Safety goggles
Dissecting scissors
Paper towels Plastic Trash bag
Precautions
1. This activity should be done in pairs or singly.
2. Bring your own dissecting set with pans.
3. Do not leave your lab station.
4. Treat the lab equipment with respect.
5. Do not stab or cut the dissection pan gel
6. In the event of cut, wash the skin immediately with water and inform me
ASAP
Overview:The parts of the human eye
Procedure
1. Prior to making any incisions(cuts), examine the outside layer of the
sheep eye. Identify the following parts: The sclera, cornea, and the
optic nerve. Notice the amount of external yellow, light and dark
tissue around the eye. This tissue is fat and muscle.
2. Use the scissors to cut away the excess fat and muscle from around
the eye so the sclera and the optic nerve are clearly exposed. Be
careful when cutting around the optic nerve so that you did not cut it
away along with the fat. The optic nerve will be a “tough” tube like
structure coming out of the back of the eye.
3. The pig’s eye has 4 external attached muscles which control the eye
movement. The human eye has six. The additional muscles allow
humans the ability to “roll” and move their eyes in all directions.
4. Although the muscles of each eye work collectively as a team, the
eyes themselves do not focus or work together until months after birth.
Most people have one dominant eye. To find out which of your eyes is
dominant, form a circle with your thumb and index finger. Hold that
position and place your hand in front of you. With both eyes, look at
an object through the circle. Continue to hold that position and close
one eye then open it. Close the other eye, open it. The eye that you
could still see the object with is your dominant eye.
Which eye is your dominant eye? Left
Right (circle one)
7. Use the probe to pierce the sclera, about half way between the pupil
and the back of the eye. You will be cutting the eye in half, through
the sclera. Be careful when you cut so that you do not destroy the
pupil and lens.
8. Follow a circular pattern around the sclera, rotate the eye while
continuing to carefully cut the eye in half.
9. A clear jelly like fluid will be inside the eye. This is the vitreous
humor. Carefully lay the two sides of the eye in the dissection pan.
10.Observe the back half of the eye. You will see a dark reflective
lining. This is called the tapetum and is not found in the human
eye. This is why an animal’s eyes glow in the dark. This reflective
covering reflects light back toward the lens and allows the animals
to see better in limited light.
11.Attached to the optic nerve is a wrinkled saclike structure connected
to the back of the eye. This is the retina and is considered the
innermost layer of the eye. Just as the tapetum surrounds the
inside of the sclera, the living tissue of the retina would have been
smooth and would have rested against the tampetum. The point at
which the retinal nerve tissue connects to the optic nerve is the eye’s
blind spot.
12.Separate the retina from the back portion of the eye.
13.Remove the tapetum from the tough shell like outer layer of the
sclera and see if you can find the choroid.
14.Now observe the front half of the eye. Place the eye with the cornea
down.
15. In the front of the eye, or mixed with the vitreous humor will be a
small lens. This lens is convex and will have a slightly gray color.
In a live organism, the lens would be transparent.
16.Remove the lens from the vitreous humor. Dry it with a piece of
paper towel. Feel and feel how flexible it is. Why is the lens
flexible?
17.Hold the lens up in front of your eye, look through it. Describe how
the lens changes your vision.
18. A ring of tiny ciliary muscles are located along the inner side of the
iris. These muscles connect to the lens.
19. The pupil surrounded by the iris is on the front of the eye is the
actual opening located in the center of the pupil. The pupil is
covered and protected by the transparent living tissue of the cornea.
20.The cornea would be transparent in a living organism. Use the
tweezers and hold up the front part of the eye. Look through the
sheep pupil and cornea. How does your vision change? Why does
the cornea and lens have to be transparent?
21.ASSESSMENT: When you are finished with the dissection, raise your
hand. I will come by and ask you to identify one part of the eye.
You will have 2 chances to place the probe on the correct part. I
will record who answers correctly. NO TALKING during this time
by any lab partners.
22. Follow clean up procedures:
a) Wrap all remains in a paper towel and dispose of in the plastic
trash bag
b) All dissecting instruments, tray and gel must be thoroughly
washed in water.
c) The gel should be in the dissection pan, cover with a clean dry
paper towel.
d) All used gloves are to be disposed of the trash bag.
e) All lab aprons and goggles returned to the designated place.
f) Nothing is in the sinks at your lab station. If any material is in
the sink, use a paper towel to remove and dispose of the paper
towel in the trash bag.
g) Lab stations are clean and free of water/waste
h) Each person washes their hands with soap and water
Eye Dissection
This page must receive a stamp when completed and be turned in
along with the other senses lab experiment data tables.
Copy cut and past the post lab questions into a word document.
Dissected Eye
After performing the sheep eye dissection, show your dissected eye with the
parts arranged in the tray much as they are above to earn a stamp.
Identify the numbered parts and write their function below
Part
1
2
3
4
5
6
7
8
9
10
11
12
Function
Observe the eye model. Examine the extrinsic muscles
Post Lab Questions
MATCHING: Use the Key Terms below. Terms may be used more than once, in
combination or not at all.
a. aqueous humor
b. cornea
c. vitreous humor
d. ciliary
body/muscle
e. lens ab. conjunctiva ac. fovea
centralis ad. optic disk
ae. retina
bc. sclera bd. suspensory
ligament be. circular iris
cd. pupil ce. choroid
de. Optic nerve abc.
Extrinsic eye muscles. abd. Tapetum lucidum
abe. radial
iris BCE. None of these
1. Aims the eye.
2. Contains muscle that controls the shape of the lens.
3. Nutritive (vascular) layer / wall of the eye
4. The blind spot.
5. Layer/wall of the eye containing the neuron receptors.
6. Gel-like substance filling the posterior cavity of the eyeball.
7. Helps to maintain the placement of the retina as well as the eyeball shape.
8. Intrinsic muscle of the eye.
9. Attaches the lens to the ciliary body/muscle.
10. Fluid that fills the anterior chamber of the eye.
11. Layer/wall of the eye composed of tough, white fibrous collagen connective
tissue.
12. An area of the retina that lacks photoreceptors
13. Area of acute or discriminatory/sharpest vision
14. Refractory mediums of the eye. (name all)
15. Most anterior and transparent part of the outer wall of the eyeball.
16. Rich in mucous membranes and glands to lubricate the eye
17. Operates to dilate the iris to enlarge the pupil size
18. Transmits the action potential from the retina to the optic tract.
19. Area where the largest number of cones can be found
20. Increases night vision in animals
Match the functions. Use the word bank: a. superior oblique b. inferior
oblique c. superior rectus
d. inferior rectus e. medial rectus ab. lateral
rectus
21. Moves the eye up and out to the side
22. Moves the eye straight up
23. Moves the eye down and in toward the nose