Cow Eye Dissection

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Cow Eye Dissection
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Objectives

• By the end of this lesson, students will be able
  to
• Demonstrate proper dissection safety techniques.
• Explore and identify the external anatomy of the
  cow eye.
• Explore and identify the internal anatomy of the
  cow eye.
• Compare and contrast human and cow eye anatomy
• Evaluate how the structure of the parts of an
  eyeball relate to its function.

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Arkansas Frameworks

Grade 6 Grade 7 Grade 8
LS.2.6.1 LS.7.1.2 LS.8.1.8
LS.2.6.2 LS.7.1.3
LS.2.6.3 LS.7.1.4
LS.2.6.4
LS.2.6.6
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Why Dissect?

• Dissection allows students to
• Practice safety procedures
• Construct science process skills
• Organize the hierarchal relationships of tissues,
  organs, organ systems and organisms
• Compare similarities and differences among
  organisms
• Connect organism complexity to its diversity

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Materials

• Cow eye specimen
• Dissection tray or Styrofoam meat tray
• Dissection kit with scissors, pins, scalpels,
  tweezers and probes
• Gloves
• Goggles
• Plastic aprons
• Student worksheets

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General Safety Rules

• The classroom should be well ventilated
• Work space should be flat and free of unnecessary
  materials
• All equipment should be clean and unbroken
• ABSOLUTELY no eating, drinking or gum chewing
  during dissection activities

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Sharp Instrument Safety

• Prepare a container for disposal of broken
  instruments or glassware
• Dispose of the container intact and replace with
  a new one to prevent others from being cut
• Inventory all sharp items to ensure all objects
  remain in the classroom
• Ensure that students use sharp instruments
  properly.
• Remind students they should always cut away from
  themselves and others

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Before we proceed

• While dissecting, be respectful of your lab
  partners and of the specimen you are about to
  explore, observe and learn from.
• Take extra care with your dissection tools. Your
  scissors are your most important tool, but be
  sure to handle them carefully and always double
  check before cutting.
• If you have any questions, please ask.

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Attire

• Wear Gloves
• Wear Aprons
• Wear Goggles (ANSI Z87.1)
• Always!! No Exceptions!!!!

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Interesting Facts

• Look all around without moving your head. Look
  up, look down, look side to side and all around.
  You have six muscles surrounding your eye that
  allows you to look in different directions.
  However, cows only have four muscles. Therefore,
  they can only look up, down, left and right.
  They are not able to roll their eyes like you
  can.

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Interesting Facts
Muscle

• Reach up and feel around your eye. Can you feel
  the bone of your skull? Fat surrounds your
  eyeball to keep it from bumping against the bone
  and getting bruised.
• The fat and muscle surrounding the cow eye is cut
  away when dissecting in order to see the eyeball.
  

Fat
Optic Nerve
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External Anatomy

• Obtain a cow eye, place it in your dissecting pan
  and rinse with water.
• Observe the white part of the eye. This is the
  sclera. The sclera is the outer covering of the
  eyeball.

Sclera
Sclera
Fat
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External Anatomy
Eyelid

• Locate the eyelids.
• Observe the blue portion of the eye. This is the
  cornea. The cornea starts out clear but becomes
  cloudy after death.
• Look through the cornea and locate the iris. The
  iris is a round black tissue.
• Locate the pupil. The pupil is the round opening
  in the center of the eye.

Cornea
Pupil
Iris
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External Anatomy

• On the opposite side of the cornea, locate the
  optic nerve. The optic nerve is a white cord on
  the back of the eye about 3 mm thick.
• The following video will review what weve
  learned about the external anatomy of the eye.

Optic Nerve
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Incision 1
Sclera

• Now remove the fat and muscle surrounding the eye
  using caution not to remove the optic nerve.
• Place the eye in the dissecting pan so it is
  again facing you. Using your scalpel, pierce the
  white part of the eye (sclera) just behind the
  edge of the cornea. Make a hole large enough for
  your scissors.

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Incision 2

• Using your scissors, carefully cut around the eye
  using the edge of the cornea as a guide. Lift
  the eye and turn it as needed to make the cut and
  be careful not to squeeze the liquid out of the
  eye.

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Internal Anatomy

• If a fluid should ooze out, it is called the
  aqueous humor. This fluid is clear and made of
  protein and water. The aqueous humor helps give
  the eye its shape.

Aqueous Humor
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Internal Anatomy

• After completing the cut, carefully remove the
  front of the eye and lay it in your dissecting
  tray.
• Place the back part of the eye in the pan with
  the inner part facing upward.

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Internal Anatomy

• Observe the tough tissue of the removed cornea.
  Cut across the cornea with your scalpel to note
  its thickness.
• Observe the iris. The iris is the black tissue
  of the eye that contains curved muscle fibers
• Locate the ciliary body. It is located on the
  back of the iris that has muscle fibers to change
  the shape of the lens.

Ciliary Body
Pupil
Iris
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Internal Anatomy
Retina

• Locate the lens. It can be found by looking
  through the pupil.
• Using your scalpel and dissecting needle,
  carefully lift and work around the edges of the
  lens to remove it.
• The gel the lens is suspended it is called the
  vitreous humor.

Lens
Vitreous Humor
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Internal Anatomy

• Observe the back of the eye after the lens has
  been removed. It should be shaped like a bowl.
  On the inside of the bowl is a thin film with red
  blood vessels running through it. This is the
  retina.
• The retina is attached to the back of the eye at
  just one spot. It is called your blind spot.
  Use forceps to separate the retina from the back
  of the eye to see the layer beneath it.

Retina
Blind Spot
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Internal Anatomy

• The layer beneath the retina is called the
  tapetum. It is a shiny, blue-green layer
  designed to assist night vision by reflecting
  light back through the retina. Humans do not
  have a tapetum. This structure is responsible
  for the shining of animals eyes at night.

Tapetum
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Clean Up

• Place all dissecting specimens and parts into
  approved container provided by the instructor.
• Wash dissecting equipment and trays in dilute
  bleach solution provided by the instructor.
• Dry equipment thoroughly to prevent rusting.
• Clean table tops with dilute bleach solution
  provided by the instructor.
• Wash hands thoroughly before leaving the
  classroom.

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Resources

• Cow Eyeball Dissection
• http//www.exploratorium.edu/learning_studio/cow_
  eye
• Cow Eye Dissection, worksheet, lab
• http//www.dishs.org/webpages/dalpoggettom/Phisic
  alScience/coweyedissection.htm
• Cow Eye Dissection
• http//www.cas.vanderbiltedu/bsci111b/eye/cow-eye
  /cow-eye-dissection.htm
• Dissection Narrative
• http//www.seq.org/-ca_science/Silva/HumanBio/Uni
  ts/Nervous/eyedissection.doc