Learning Eye Physiology through Optical Illusions!

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Objective

Students will apply observations from optical illusion activities to infer physiology of specific eye parts.

Big Idea

The different parts of the eye can cause the optical illusions that highlight their functions.

Introduction

Lesson Background & Justification:

       The Eye is an organ of vision that detects light from the environment and converts it into electro-chemical impulses in neurons. In higher organisms like humans, the eye functions as a complex optical system comprised of specialized tissues and fluids which cooperatively work together to collect and regulate light from the surrounding environment, focus it, form an image, and convert the image into a set of electrical signals that transmits the signal to the visual cortex of the brain through complex neural pathways that connect to the eye via the optic nerve. In this lesson, students learn to describe and evaluate the locale and function of the eye's cellular and chemical components in the effort to understand the underpinnings or molecular events that dictate how the components of the eye explored in lesson 1 of this unit are capable of performing their functions in a repetitive and streamlined fashion. Command of this content presented in this  lesson later serves as a primer for students to comprehend how the molecular events involved in the other senses that are presented later in this unit are chemically and structurally ideal to selectively process elements or stimulants from our environment for transmitting information to specific regions of the brain that are responsible for processing and remembering them.  

Essential Prior Knowledge: Prior to experiencing this lesson, students should be familiar with the following content/concepts:

             a) Structure and Function of Neurons  

            b) Organization/Hierarchy of organisms   

Lesson Preparations:

 In the effort to prepare for this lesson, I make certain that I have the following items in place: 

a) A class set of the Snellen Eye Chart Activity and Investigating Your Sense of Sight Activity Sheets (One copy of each per 4 students).

b) A class set measuring tapes (1 per student group of 4)

c) A class set of tape and scissors.

d) Student lab books.

e) A class set of Eye Anatomy and Physiology Notes (see attachment)

Common Core and NGSS Standards:

MS-PS4-2-Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

SP2- Developing and Using Models.

XC-SF-HS-1-Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Standards Rationale:

       Modeling is the process by which scientists represent ideas about the natural world to each other, and then collaboratively make changes to these representations over time in response to new evidence and understandings. It is intimately connected to other scientific processes (asking questions, communicating information, etc.) and improves students ability to recall scientific jargon through association. In the classroom, it is important that teachers engage students in modeling practices, to set the foundation of success in a lesson or instructional unit. In this lesson modeling is used in concert with other science practices in the classroom to promote students’ reasoning and understanding of core science idea presented (structure and function of the eye). 

Engage

10 minutes

Section Primer: 

        A visual prosthesis, often referred to as a bionic eye, is an experimental visual device intended to restore functional vision in those suffering from partial or total blindness. In this part of the lesson, students are exposed to the idea of a bionic eye proceeding the review of eye parts and their corresponding functions. The idea is to recap the concept of how sight occurs and then to encourage students to apply this knowledge to propose or hypothesize how a potential mechanical eye prosthetic could be manufactured to remedy blindness.    

Section Sequence:

a) Slide 1: Review eye parts and function via simple Q and A using the image projected and proceed to read and discuss the remaining questions as a class in the progression displayed on on the slide. Within the discussion, encourage students to verbally support their mechanical substitutions proposed by explaining how they believe the form of their proposals fit the eye parts that they are replacing.  

b) Share with students that scientists have explored said prosthetic and are aiming to treat different patients based on their cause and degree of blindness. Then play the following video to share the science with students: 

     

c) Post video, compare and contrast student proposals with those seen in the video. Discuss as a class what parts of the eyes have the greatest responsibility of transmitting light information to the brain based on the nature and placement of the devices observed in the video. 

Standards Covered:

MS-PS4-2-Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

SP2- Developing and Using Models.

XC-SF-HS-1-Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Explore

30 minutes

Section Primer:

     A Snellen Chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch opthalmologist Herman Snellen who developed the chart in 1862. The visual acuity test is used to determine the smallest letters you can read on a standardized chart (Snellen chart) or a card held 20 feet away. Special charts are used when testing at distances shorter than 20 feet. In this section of the lesson, students explore their own visual acuity to gain a general sense of what is average among a population before delving into how acuity is biochemically achieved.      

Section Sequence:

a) Slide 2: Provide student groups with a copy of the Snellen Chart. Then read and proceed with instructions as they appear on the presentation slide. 

b) Post activity, bring the discussion full circle by asking students what 20/20 vision means and if the group as whole have the same visual acuity. Finally, share that we will examine the physiology of the eye closer to further explain why there is such diversity in visual acuteness even in small sample of the world's population like their class. 

Standards Covered:

SP2- Developing and Using Models.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Explain

20 minutes

Section Primer: 

       The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones. In this section of the lesson, students learn to develop a chemical explanation of the molecular events that creates vision. 

Section Sequence:

a) Slide 3: Use the diagram presented to show the general flow of light in the eye. Ask students why they think that the light bypasses 2 levels of cells before being processed/absorbed. Try to encourage students to verbalize that the first two layers are not specialized to absorb light. 

b) Slide 4: Instruct students to label the various types & layers of cells that make up the retina on the diagram located at the top of the second sheet in their Anatomy and Function handouts. Then play the General Physiology of the Eye video and instruct students to develop notes that focus on the physiology of the labeled cells. Discuss notes post video for clarification.

c) Slide 5: Use the diagram on the slide and student rod and cone diagrams in their packets to instruct students on how to label the parts of the rod and cone cells. Discuss how these nerve cells are structurally similar and different than motor neurons. Place emphasis on the segments with discs which are specialized to receive light but have no dendrites to receive chemical messages or Nt's. Note that they do possess axon terminals to dispense Nt's however. This is key in the light to chemical transmission process. 

d) Slide 6: Use the diagram on the slide and student rod and cone diagrams in their packets to instruct students on how to compare and contrast  these cells and their responses to light.   

e) Slide 7: Use the diagram on the slide and student biochemistry of rod diagrams on page 3 in their packets to instruct students on how to explain the details of the rod and cone cell activity seen on the slide (focusing on rods) and in the following video Cone Chemistry and Physiology  (focusing on cones). Discuss notes post video for clarification.

Standards Covered:

MS-PS4-2-Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

SP2- Developing and Using Models.

XC-SF-HS-1-Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Extend

20 minutes

Section Primer:

     Optical Illusions can use color, light and patterns to create images that can be deceptive or misleading to our brains. The information gathered by the eye is processed by the brain, creating a perception that in reality, does not match the true image. In this section of the lesson, students explore a variety of optical illusions and attempt to rectify their observations by using the science that explains eye physiology under normal or optimal conditions. 

Section Sequence:

a) Slide 8: Provide student pairs with copies of the activities outlined in the Investigating Your Sense of Sight handouts (pages 1-4).

b) Instruct students to follow the instructions outlined on the projected slide and discuss their findings post activity as a class. Encourage students to provide explanations that incorporates jargon specific to the eye's anatomy and its physiology. In other words, I am requiring students to use vocabulary from the previous lesson.

Standards Covered:

MS-PS4-2-Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.

HS-LS1-2- Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

SP2- Developing and Using Models.

XC-SF-HS-1-Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem.

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. 

Evaluate

10 minutes

Section Sequence:

       In this section of the lesson, my goal is to have students reflect on the functions of the two major cells that are are most active in processing light (rods and cones) by completing a chart that compares and contrasts their function.  

Slide 9: Instruct students to locate the chart seen on the slide in their handouts and complete the assignment. Students should submit the assignment upon completion. 

Standards Covered:

MS-LS1-8- Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.