Teacher Notes
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Teacher Notes![]() Modeling Eye OpticsClassroom SetMaterials Included In Kit
Accordion bottles, 4
Acetate sheet Corrective lenses, concave, 50 mm, 150 mm focal length, 4 Corrective lenses, convex, 50 mm, 150 mm focal length, 4 Eye lenses, 38 mm, 100 mm focal length, 4 Filter paper, 9 cm diameter, 20 sheets Lens holders, 4 Additional Materials Required
Flashlight or other bright light source
Meter stick Permanent marker, black (for teacher) Scissors or papercutter (for teacher) Towels or books, 3–4 Transparent tape Prelab Preparation
Safety PrecautionsIf a candle is used as the light source, caution students about the dangers of an open flame and of the high flammability of the “retina” paper. Follow normal laboratory safety guidelines. DisposalAll the materials may be saved for future use. Teacher Tips
Sample DataNormal Eye The image of the “E” on the “retina” is larger than the real “E.” The image is upside-down compared to the real “E.” Squeezed EyeLength: ___13.8 cm___ Initial observations of the image on the “retina”: The image is very blurry. The image of the “E” cannot be seen. A dark region is visible in the center of the bright spot. Lens used to bring the “E” into focus: convexDistance between the external lens and the “eye’s” lens when the image is in focus: ___10.3 cm___ Final observations of the focused image using a corrective lens: The image of the “E” is in focus again. The image is smaller than the original image produced by the “normal eye.” The image is upside-down and does appear a bit clearer than before. Elongated EyeLength: ___23.0 cm___ Initial observations of the image on the “retina”: The image is very blurry just like it was for the “squeezed eye” case. The image of the “E” cannot be seen. A gray region is visible in the center of the bright spot. Lens used to bring the “E” into focus: ___concave___ Distance between the external lens and the “eye’s” lens with the image is in focus: ___10.2 cm___ Final observations of the focused image using a corrective lens: The image of the “E” is in focus again. The image is much smaller than the original image produced by the “normal eye.” The image is upside-down and is not as bright as the original image. Answers to QuestionsNormal Eye
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Student Pages
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Student Pages![]() Modeling Eye OpticsIntroductionThe human eye is intricate and complex. To truly understand how the eye works, various elements of physics, anatomy, physiology, biochemistry and nutrition must be studied. This activity will illuminate the physics (optics) principles involved in the functioning eye. Concepts
BackgroundA sketch of the anatomical parts of the human eye is shown in Figure 1. {12664_Background_Figure_1}
A discussion of the role of each part of the eye is not included in this discussion. These details are covered in most high school biology textbooks and on many websites.A realistic understanding of how the eye works started around the 17th century. It was realized in the 17th century that the retina at the back of the eye, and not the cornea as previously thought, was responsible for the detection of light and therefore sight. Johannes Kepler (1571–1630) of Germany and René Descartes (1596–1650) of France, both prominent scientists, made many advances in understanding how the eye functions. Kepler, most famous for his laws of planetary motion, was the first to propose that the lens of the eye focuses images onto the retina at the back of the eye. A few decades later, Descartes demonstrated that Kepler was correct. Following up on experiments performed by another scientist, Descartes surgically removed an eye from an ox and scraped the back of the eye to make it transparent. He then placed the eye on a window ledge as if the ox were looking out the window. When he looked at the back of the eye, Descartes saw an inverted image of the scenery outside. Descartes correctly hypothesized that the image was inverted as a result of being focused onto the retina by the eye’s lens. Descartes was actually one of the first to realize a corneal contact lens could be used to correct vision. In this activity, a model eyeball will be constructed and a more humane and less gory version of Descartes’ ox eye experiment will be repeated. In addition, several common eye correction procedures will be simulated with the working eye model. The model will demonstrate two common refraction disorders—nearsightedness (myopia) and farsightedness (hyperopia). An individual who is nearsighted can easily see objects that are up close, but objects that are far away are out of focus and blurry. Farsightedness is a condition in which an individual can clearly see objects that are far away, but has difficulty seeing objects that are close. Both of these conditions are the result of the eye’s inability to focus the image directly on the retina. For nearsightedness, the lens is not expanded enough to increase the focal length when viewing objects at a distance, and for farsightedness, the lens is not squeezed enough to shorten the focal length in order to view a nearby object. The failure of the lens of the eye to change shape often occurs as the body ages because the ciliary muscles regulating the shape of the lens deteriorate and become weaker. Another reason for the lens not being able to focus light directly on the retina is because the eye is too long or too short relative to the range of focal lengths the lens can attain. The net result of a misshaped eye is that the image is focused short of the retina (2a) or beyond the retina (2b) and produces a blurred image. See Figure 2 showing the two conditions. {12664_Background_Figure_2}
Corrective lenses, such as eyeglasses or contact lenses, placed in front of the cornea assist the eye in converging or diverging light rays, which allows the eye’s lens to focus the image directly on the retina to produce clear vision.
Materials
Accordion bottle
Books or cloth towels, 3–4 Corrective lens, concave, 50 mm Corrective lens, convex, 50 mm Eye lens, 38 mm Filter paper Flashlight Lens holder Meter stick Transparency with “E” Transparent tape Safety PrecautionsAlthough this activity is considered nonhazardous, please follow all normal laboratory safety guidelines. ProcedurePart A. Normal Eye
Student Worksheet PDF |