The structures of the human eye collect and focus light, forming an image on the retina at the back of the eye. The image is converted to electrical signals that travel to the brain, which interprets the signals and “tells” us what we are seeing. Common vision problems include nearsightedness (myopia), which can be corrected with concave lenses, and farsightedness (hyperopia), which can be corrected with convex lenses.
- AAAS.6-8.4.F.2, 6; AAAS.6-8.12.D.4
- Describe the structure and function of the eye.
- Explain how the eyes and brain work together to enable vision.
- Identify common vision problems and how they can be corrected.
Introducing the Lesson
Introduce the eye and the upside-down images it forms by asking students to imagine what it would be like if everything they saw was upside down. Give students a chance to experience this by holding a plane mirror in front of them so that it reflects the ceiling. Tell them to take a few steps while holding the mirror in this way (make sure they do this where there are no objects on the floor to trip them). They will know they are walking on the floor but will have the odd sensation of walking on the ceiling. Explain that the eye actually does form upside-down images, yet everything we see appears to be right-side up as it really is. Tell students they will learn how this happens when they read this lesson.
To introduce the roles of the eye and brain in the perception of objects, including their color, use the activity at the URL below. The Web site includes a student worksheet and slideshow. Also provided are discussion questions, ideas for assessment, and extensions.
The interesting demonstration at the following URL will help students understand eye anatomy by finding the blind spot in their own retinas. Explain that the blind spot is an area on the retina without light receptors, so an image that falls on this area cannot be detected. It is in this area that the optic nerve exits the eye on its way to the brain.
The video-based interactive activity at the URL below gives students a close-up view of the anatomy of a real cow’s eye as it is dissected by a teenaged narrator. The Flash movies are divided into 12 segments which may be stopped and restarted interactively. Each segment contains text information with vocabulary definitions in a "hover-over" format. The resource also provides a diagram of the eye and detailed illustrations that show how the eye refracts light and sends messages to the optic nerve.
Suggest that students make a simple flow chart to summarize how light passes through the eye and how the light is affected by each structure it passes through.
Ask a few interested students to explore the topic of optical illusions to show the importance of the brain in vision. Have them find several online examples of optical illusions to share with and explain to the class. The following URLs are good places to start.
Challenge small groups of students to make cross-sectional models of the human eye, following the guidelines at this URL: http://mesa.ucop.edu/mesa_day_rules/Model_Science_The_Human_Eye_2012-2013.pdf.
Common misconceptions about the human eye include the following:
- The pupil of the eye is a black spot on the surface of the eye.
- The eye perceives upright images.
- The lens forms a picture on the retina, and the brain “looks” at this picture
Address these misconceptions and explain why they are incorrect. For example, for the third misconception, explain that images on the retina are converted to electrical signals that travel to the brain through the optic nerve and that the brain then interprets the electrical signals as images.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook®.
Check students’ mastery of the lesson with Lesson 22.3 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
This chapter focuses on energy in the form of visible light. Another common form of energy, electrical energy, is the focus of the chapter “Electricity.”
- What are some ways you use electrical energy?
- Where does the electrical energy you use come from?