Science 8 Name Eyeball Model Lab Date Block Problem: Identify the twelve key parts of the eye and describe their function. Materials: dissecting scissors ping pong ball transparent plastic ordinary scissors plastic cushion aluminum foil transparent tape tissue paper construction paper glue stick string ruler Procedure: (place a checkmark on each step once you have done it) 1. Use a pencil to sketch the following on the ping pong ball: a) a line following the circumference of the ball along the seam b) a circle on the front (about 2 cm in diameter) c) a circle about 0.5 cm in diameter on the bottom back d) print your first and last name 2. Use the dissecting scissors to carefully cut the following in this order (reverse order of above #1): a) the small circle on the bottom back b) the big circle on the front c) the circumference of the ping pong ball along the seam 3. The outside shell of the eye is called the sclera. For this model, we are using the white ping pong ball to represent the sclera. (No action is required for this step). 4. Cut a piece of aluminum foil to fit the inside back of the eyeball. This represents the choroid coat. It contains blood vessels that provide nutrients for the eye. Shape the aluminum foil and then use glue so that it attaches to the inside back of the eyeball. 5. Cut a piece of tissue paper to fit the inside back of the eyeball. Place the tissue paper on top of the aluminum foil. This represents the retina. It is a receptor containing rods and cones which identify shapes (rods) and colours (cones) from light. 6. Tie a knot on the end of a piece of string. Use the dissecting scissors to punch a small hole in the retina and choroid coat so that the string can exit the eye via the hole you cut previously. Lead the string through the hole so that the knot is in the inside. It represents the optic nerve. It transfers the information from the retina to the brain.
7. Light landing anywhere on the retina (tissue paper) is processed and the information is sent to the brain. The only place where this can t happen is the place where the optic nerve attaches to the retina (at the knot). This connection is called the blind spot. (No action is required for this step). 8. Cut a piece of transparent plastic that can be taped over the large hole at the front of the eye, and tape it over the large hole. The plastic represents the cornea. It acts as a lens to focus the light and also protects the eye. 9. Cut a circular piece of coloured construction paper that is about 2.5cm in diameter. Now cut an inner hole in the construction paper so that this second hole is smaller than the hole in the front of the eyeball. Tape this coloured paper to the inside of the eyeball. This represents the iris. It dilates or contracts to allow more or less light into the eye. 10. The hole in the middle of the iris is the part that actually lets the light into the inside of the eyeball. It is called the pupil. (No action is required for this step). 11. Tape the plastic cushion to the inside of the iris by centering it in the pupil. This represents the lens. It does the final focusing of the light that enters your eye. 12. The plastic cushion (the lens) is rigid but the lens in your eye is flexible. The ciliary muscles (the tape around the lens) are responsible for changing the thickness of the lens, which adjusts for objects that are near or far away. (No action is required for this step). 13. In between the lens and the front of the eye (the cornea) is a liquid, which we cannot duplicate in our model because it would dribble out onto the floor! It is called the aqueous humour. This is a watery fluid that carries nutrients to, and wastes away from the front of the eye. It also keeps the shape of the front of the eye and prevents the cornea from collapsing upon the lens. (No action is required for this step). 14. In between the lens and the back of the eye (the retina) is another liquid that we also cannot duplicate because it would dribble out onto the floor in our model! It is called the vitreous humour. It does the same job as air in a beach ball. This is like a jelly like liquid that gives the eyeball shape, prevents the sclera from collapsing, and holds the retina in place. This jelly-like liquid carries nutrients to and wastes away from the parts, which make up the back of the eye. (No action is required for this step). 15. Carefully match the two halves of the eyeball together and use a piece of tape around their circumference to hold them together. Politely show your teacher your eyeball model and ask him or her to initial this box showing that your eyeball is constructed correctly. Teacher s Initials
Observations: 1. What does each of these represent in the real eye? (Hint: See boldface words in procedure! Ciliary muscles has been provided) a) ping pong ball b) aluminum foil c) tissue paper d) string e) knot in the string f) transparent plastic g) coloured paper h) hole in the coloured paper i) plastic cushion j) tape around the lens ciliary muscles k) the air between the lens and cornea l) air between lens and retina 2. Fill in the following blanks. The top blank for each letter is the material that you used for the model, and the bottom blank for each letter is the name of the real part of the eye. (For example, for a) the top blank is scotch tape and the bottom blank is ciliary muscles)
Discussion: Answer each of the following questions. The sclera is more flexible than the ping pong ball but still very strong. Why do you think it is important that the sclera is tough? What is the main function of the choroid coat? Sometimes people who receive a blow to the head are diagnosed to have a detached retina. Why is a detached retina a major problem? Hint: this is why you did not attach the retina (tissue paper) when you built the model. Think about television hooked up to a cable. What part is the same as the optic nerve? What do you think you see when an image lands exactly on your blind spot? If the inside of the eye is represented by the inside of a car, what part of the eye would the windshield (which lets light in but protects the car) represent? What colour is the iris in your model eye? What is the colour of your iris (your real eye)?
What colour is the pupil in your eye? Is the pupil something you can touch? If an iris is like a donut, which part is like the pupil? Why is it important that the lens can change its shape? What causes the lens to change shape? Name the two parts of the eye that prevent the aqueous humour from escaping. Name the two parts of the eye that prevent the vitreous humour from escaping. Extension: Use what you have learned about the 12 parts of the eye discussed in this lab to write a paragraph (minimum) story of The light in the family room is on, I can see my. Use the rest of this page and the back of the page to write.