Eye see you!
Purpose: To examine the structures in the eye and to look at how the structure defines its function.
South Carolina State Standards Covered:
8-6.6 Explain sight in terms of the relationship between the eye and the light waves emitted or reflected by an object.
8-6.7 Explain how the absorption and reflection of light waves by various materials result in the human perception of color.
Performance Objectives:
- Allow the students to dissect a sheep eye with minimal instruction.
- The students should be able to identify structures in the eye from a diagram of an eye.
- The students should be able to infer why certain structures are a certain color or shape based on the function of that structure.
Materials:
- Sheep or cow eye for each pair of students
- Dissection trays
- Scissors or scalpels
Activity:
Explain how the students should do an external examination of the eye and the external structures. Explain how the students should cut into the eye without damaging any of the internal structures you would like to examine. Allow the students to identify all parts of the eye and answer questions about certain structures and their function. After the dissection, you may want to show videos from http://www.exploratorium.edu/learning_studio/cow_eye/ to further explain what the students did.
Activity A
1.) Draw the lightbulb in the white box as it would be projected onto the retina.
2.) Cones in the retina are responsible for seeing
a. Bright light and color
b. Dim light and black and white only
3.) The iris is
a. The colored part of the eye
b. Heavily pigmented
c. A muscle
d. All of the above
Activity B
1.) Label the parts of the eye in the corresponding box. You may use words from the word bank. Not all word bank terms will be used. (Iris, Pupil, Light rays, Fovea, Lens, Sclera, Retina)
2.) What is the path of light from outside the eye until the light is projected onto the retina? List the eye structures that light passes through in order below.
3.) The lens:
a. Magnifies objects
b. Makes objects appear smaller
c. Makes objects appear exactly as they are without changing the image
The Sheep Eye
External examination:
Notice all of the external parts of the eye:
Fat: protects the eye from shock in the bony socket
Muscle: moves the eye within the socket
Sclera: the tough external white coat
Cornea: the transparent portion of the sclera covering the iris and pupil.
1.) Why is the cornea transparent?
Optic nerve: on the back side of the eye, it is a cord of nerve fibers that transmit the information you see to your brain.
Carefully use your scissors to cut the eye in half around the sclera as shown by your instructor.
Internal examination:
2.) A dark liquid may have come out of the sheep eye, is it the aqueous humor or the vitreous humor? How do you know?
3.) A clear gelatinous substance may have come out of the sheep eye, is it the aqueous humor or the vitreous humor? How do you know?
Lens: held in place by the suspensory ligaments and the black ciliary body. The lens focuses images on the retina allowing you to see a clear, sharp image. The lens changes shape to allow you to focus on objects at different distances. The suspensory ligaments and the ciliary body help the lens change shape.
4.) Remove the lens from the eye and place it on a word or letter on this paper. Describe what you see through the lens.
5.) Hold the lens up and focus on an object in the room through the lens. Describe what you see through the lens.
Iris: a heavily pigmented muscle that controls the size of the pupil.
Pupil: the circular opening that allows light into the eye. The larger the pupil is, the more light it allows into the eye. The pupil is typically large in dim light, and small in bright light.
Choroid: a dark iridescent tissue that gets it’s iridescence from the tapetum lucidum (absent in human eyes) that reflects light onto the retina.
Retina: the delicate, white , inner coat beneath the choroid coat.
6.) Separate the choroid coat from the retina. The retina attaches to the back of the eye in one single spot. What is this spot called?
7.) What is the path of light as it comes into your eye and is projected onto the retina?
Cones: neurons in the retina which are responsible for bright-light vision, detail, and color. Cones are concentrated in the center of the retina at the fovea and are more spread out away from the fovea. A color-blind person does not have functioning cones. This is a gender-linked disorder on the X-chromosome, and typically only affects males.
Rods: function in dim light and are insensitive to colors. Rods are more numerous away from the fovea.