Cow Eye Dissection

Introduction:
How do we see? The eye processes the light through photoreceptors located in the eye that send signals to the brain and tells us what we are seeing. There are two types of photoreceptors, rods and cones. These photoreceptors are sensitive to the light. Rods are the most sensitive to light and therefore provide gray vision at night. Cones are mainly active in bright light and enable you to see color. There are 100 million rods compared to the 3 million cones located in your retina. The photoreceptors help you adjust to night and day. For example, if you walk inside from the sun, you can not initially see anything. This is due to the activity of the cones and the lack of activity of the rods. The rods become activated and adapted to the dim light, resulting in gray images formed in the dark. The same thing happens when you leave a dark movie theatre during the day. The rods are mainly activated and the cones have to adjust to sunlight when you leave the theatre.

Objective: 
By dissecting the eye of a cow, which is similar to the eyes of all mammals including humans, you will gain an understanding of the structure and function of the parts of the eye.

Materials:
Cow eye, dissecting pan, dissecting kit, safety glasses, lab apron, and gloves

Procedure (External Structure):

  1. Obtain a cow eye, place it in your dissecting pan, & rinse the eye with water.
  2. Rotate the eye until the larger bulge or tear gland is on the top of the eye. The eye is now in the position it would be in a body as you face the body.
  3. On the outside of the eye, locate the following parts:
  1. Turn the eye so that it is facing you & examine these structures on the front surface of the eye:

Click here for labeled eye model

Procedure (Internal Structure):

  1. Place the eye in the dissecting pan so it is again facing you. Using your scalpel, pierce the white part of the eye or sclera just behind the edge of the cornea. Make a hole large enough for your scissors.
  2. Using your scissors, carefully cut around the eye using the edge of the cornea as a guide. Lift the eye & turn it as needed to make the cut and be careful not to squeeze the liquid out of the eye.
  3. After completing the cut, carefully remove the front of the eye and lay it in your dissecting pan.
  4. Place the back part of the eye in the pan with the inner part facing upward.
  5. Locate the following internal structures of the eye:

10. Answer the worksheet questions on the cow eye dissection.

Click here for eye dissection questions

  1. Dispose of the eye as your teacher advises and rinse and return all equipment to the supply cart. Wash your hands thoroughly.

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