Lesson Understanding the Structure of the Eye

Learning Objectives

After this lesson, students should be able to:

• Identify components that make up the eye.
• Explain causes of color blindness.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Introduction/Motivation

(In advance, make copies of the Eye Structure and Seeing Light—Notes Outline, In and Out of Focus Worksheet and Eye Anatomy Quiz, one each per student. Also [optional], prepare to show students the attached 11-slide Eye Structure and Seeing Light Presentation to accompany the lesson introduction. The slides are "animated" so you can click to show the next item when ready.)

So far, we have been learning all about waves and light. But think back to our original engineering challenge about color blindness. We need to complete our research; we need to find out about the human eye, and how we see light before we will be able to design a solution to our problem. That's what we will be doing today!

(Hand out the notes outlines and present the lecture material provided in the Background section, in tandem with the slides.)

(Next, have students conduct investigative experiments, as guided by the worksheet and using materials listed in the Background section. Lead in with the following introduction.)

When an object gets too close to the eye, the lens can no longer focus on it and it becomes blurry. At what distance does this happen? Does it vary with different people and ages? Does the shape or color of the object make a difference? Today, you will do your own investigative tests and measurements to find out the vision limitations of test subjects.

(After the experiments, conclude with a concluding discussion and quiz, as described in the Assessment section. Then conduct the culminating associated activity Developing & Presenting Design Solutions: Waves Go Public!.)

Lesson Background and Concepts for Teachers

Legacy Cycle Information: This lesson falls into the research and revise phase of the legacy cycle. During this phase, students learn more about the basic concepts required to design solutions to the engineering challenge presented in lesson 1 of this unit. After lesson 5, students should be able to revise their initial thoughts, forming new ones that will help solve the engineering challenge.

Eye Structure and Seeing Light

(The following lecture material aligns with the slides.)

The eye is like a camera: light enters, is focused on a surface, and a picture is made. Light enters your eye through a clear portion of the sclera (the tough, white, outer covering of the eye), called the cornea.

The cornea is curved, so it slightly bends the light as it goes through. Light then passes through the aqueous humor (a clear fluid for eye nourishment, in the anterior chamber) and through the pupil. The pupil is simply a hole in the iris.

The iris is a muscle that controls the size of the pupil. It is the colored part of the eye. In bright light, the iris expands and the pupil gets smaller. In low light, the iris contracts and the pupil gets bigger. The color of the iris can be seen through the transparent cornea over it.

Directly behind the iris is the lens. This structure changes shape to focus light so that we can see clearly. Its shape is convex, meaning it curves outward on both sides. The ciliary muscles above and below the lens control the shape of the lens.

Behind the lens is a clear gel called the vitreous humor. After moving through the vitreous humor, light strikes the retina, which is the lining on the inside of the back of the eye that contains two types of light-sensitive cells: rods and cones.

Rods sense black and white and can work in low light. Cones sense color and must have more light than rods to work. Three kinds of cones exist: L-cones sense long wavelengths in the red range; M-cones sense mid-range wavelengths in the green range; and S-cones sense short wavelengths in the blue range.

The rods and cones send messages to the brain via the optic nerve, and the brain makes sense of all the information it receives. In your brain, the sight center is located the back of your head (basically between your ears) which is why a blow to the back of your head might result in blindness, even though your eyes are undamaged.

The causes of color blindness (aka color deficiency) fall into two categories:

• Genetic: You are born with these types. Sometimes a type of cone is missing, or the cone does not recognize the correct wavelengths of light. L-cone and M-cone problems result in red-green color blindness, the most common type.
• Non-Genetic: These types occur after birth. For example, accidents involving the vision center of the brain, cataracts, glaucoma; Parkinson's Disease can cause S-cone problems, and diabetic retinopathy can also affect color vision.

Experiments to Research and Gather Information

To find out the vision limitations of people, we do tests. Have students experience this investigational aspect of design by conducting their own experimentation, as guided by the In and Out of Focus Worksheet, in which they test other students to find out more about what makes an object look blurry. As an object approaches the human eye, the lens flexes to focus on it. Eventually the object gets so close, however, that the lens can no longer focus on it. At that point, the object begins to blur. Have available the following materials for each student team to use.

• 2.5 cm x 5 cm (1-in x 2-in) clipping of printed words from a newspaper or magazine
• 3-in x 5-in index card
• modeling clay or sculpting compound
• cloth or soft vinyl tape measure, such as those used in sewing
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Associated Activities

• Developing & Presenting Design Solutions: Waves Go Public! - Students apply everything they have learned about waves, light properties, the electromagnetic spectrum, and eye anatomy, to design devices that can aid color blind persons in distinguishing colors. Students learn about the engineering design process and teams develop three possible solutions to the unit's design challenge. Through this activity, teams complete the legacy cycle by "going public." They illustrate and compare the three potential solutions on posters. They create informative brochures that explain the final designs and the science behind them. And, they make three-minute presentations to pitch the ideas.

Vocabulary/Definitions

anterior chamber: The fluid-filled space inside the eye between the iris and the cornea; it is filled with aqueous humor.

aqueous humor: The clear fluid behind the cornea; provides eye nourishment.

choroid: A vascular layer (includes blood vessels) of the eye containing connective tissue; it is located between the sclera and the retina.

cornea: The clear portion of the eye through which light enters.

fovea: A part of the eye located in the center of the retina that is responsible for sharp central vision, which is so important in humans for reading, watching, driving or any activity in which visual detail is important.

iris: The colored part of the eye; a muscle that controls the pupil size.

lens: A structure that changes shape to focus light so that we can see clearly; located directly behind the iris.

optic nerve: A cranial nerve connected to the eye socket that transmits visual information from the retina to the brain.

pupil: A hole in the iris.

retina: The lining on the inside of the back of the eye that contains two types of light-sensitive cells: rods and cones.

sclera: The tough, white, outer covering of the eye.

vitreous humor: A clear gel behind the lens, inside the eye.

Assessment

Note Taking: During the lecture, have students complete the Eye Structure and Seeing Light—Notes Outline and refer to it for visuals that supplement the lecture material. Then, with the notes turned over on their desks, ask students various questions that were covered in the lecture material. Evaluate students' answers to gauge their mastery of the subject.

Worksheet: After the lecture, guided by the instructions on the In and Out of Focus Worksheet, have students conduct their own investigative tests and measurements to find the vision limitations of test subjects. Evaluate students' answers to gauge their comprehension of the subject.

Concluding Discussion: Once the worksheet questions are completed and handed in, lead a class discussion to share results and conclusions. Possible discussion questions:

• How close can you bring an object before it looks blurry?
• What is the average distance where the image begins to blur for all test subjects?
• Does this distance vary for different people or age groups?
• Is the average distance larger or smaller for people who wear glasses?
• Is it larger or smaller for one eye or both eyes?
• Is the distance the same for both eyes of the same person?
• Does the shape or color of the object make any difference?
• Does it matter how brightly the object is illuminated?
• What eye parts might be responsible if a person cannot focus his/her eyes or is color blind?
• How would you design another experiment that tests to investigate other vision characteristics, such as the width of a person's field of vision or if all colors are being seen?

Word Bank Post-Lesson Quiz: Have students complete the Eye Anatomy Quiz, in which they use the vocabulary terms. Evaluate students' answers to see how well they retained what they learned.

Additional Multimedia Support

Show students a 3:30-minute video of a man talking about what it is like to be color blind, at Nemour's Kids Health website: http://kidshealth.org/kid/talk/qa/color_blind.html

Show students photos that simulate color blindness, at https://www.color-blindness.com/coblis-color-blindness-simulator/

Copyright

Contributors

Supporting Program

Acknowledgements

This lesson was developed through Clemson University's "Engineering Fibers and Films Experience – EFF-X" Research Experience for Teachers program, funded by National Science Foundation grant no. EEC-0602040. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.