Dissecting a Cow’s Eye
Eyes are sensory organs that detect light. Like a camera, eyes are composed
of various parts that each have a specific function. By examining the shape,
appearance, and arrangement of the parts of an eye, you can learn more
about how the eye works.
OBJECTIVES
• Dissect a cow’s eye.
• Identify the parts of a mammal’s eye.
• Describe the function of each part of a mammal’s eye.
MATERIALS
• cow’s eye, preserved
• dissection tray
• gloves, disposable
• newspaper
• paper towels
• probe, blunt
• scalpel
• scissors
• scissors, fine point
• tweezers
DISSECTION PROCEDURE and INSTRUCTIONS
1. Put on safety goggles, gloves, and a lab apron.
• Caution: Be extremely careful when using sharp and pointed
instruments, such as scalpels.
• Get a preserved cow’s eye, dissecting tray, probe, scalpel, scissors, and
tweezers.
2. Place your cow’s eye into a dissecting tray.
• Observe the outer structure of the eye.
• Make a sketch of what you see.
• Use the image on the next page to label the following parts on your
sketch: optic nerve, cornea, pupil, iris, and muscles.
3. With a scalpel, make a small slit in the cornea to drain the clear liquid stored
under this thick covering.
• This liquid is called vitreous humor.
• The vitreous humor helps the eye maintain its shape and hold the retina
in place.
4. Use your scalpel and scissors to divide the eye in half.
• Although a sharp scalpel can slice into the eye, dissecting scissors will
help you cut through this tough tissue in a straight line.
• As you cut through the eye, more vitreous humor may come out of the
eye.
• The front half of the eye should include the cornea, pupil, and iris.
• The back half of the eye should include the retina and optic nerve.
5. Sketch the eye again.
• Use the illustration to label the following parts: lens, retina, pupil,
cornea, and optic nerve.
6. Examine the front half of the eye.
• Use your scalpel or scissors to cut out the cornea along its rim.
• Note the thickness of the cow’s cornea.
7. The removal of the cornea reveals the muscular iris and the pupil opening.
• You should be able to pull out the iris in one piece.
• Describe the appearance of the cornea and pupil.
8. Remove the lens.
• Use a paper towel to gently dry the lens.
• Use the lens to read a portion of a newspaper.
• How does the lens change the appearance of the newspaper?
9. Examine the back half of the eye.
• Note the thin sheet of tissue at the back of the eye.
• This is the retina.
• Find where the nerve fibers of the retina join together.
• Identify where these fibers exit the eye.
ANALYZE RESULTS
Data Sheet
1. Vitreous humor is the fluid that came out of the eye when you slit the cornea. Why
is the eye filled with vitreous humor?
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2. Can you remove the pupil of the eye like you could remove the lens or cornea?
What is the pupil? Explain your answer.
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What is the function of the pupil? How does the actual structure of the pupil
complement its function?
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3. An eye lens focuses light as the light enters the eye. Does the lens of an eye work
only when an animal is alive? How can you tell? (Hint: What happened when you
tried to read the newspaper with the lens?)
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4. Describe the path of light as light travels into and through the eye. Include these
structures in your description: cornea, pupil, lens, vitreous humor, and retina.
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5. A camera makes a photo by letting light in through a lens to form an image on film.
How is an eye similar to a camera?
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The shutter lets a controlled amount of light into the camera. What structure of an eye
is similar to a camera shutter?
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The light hits the film and forms an image. What structure of an eye is similar to
camera film?
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