Understanding the eye: an integrated approach
Santosh Sharma
Educationists perceive science education as being holistic in approach, allowing children to establish a relationship between skills and concepts through a systematic process of observation and deduction. However, the purpose of teaching science in school, it appears, is to ensure that students acquire adequate scientific knowledge ultimately to gain higher scores in various career-oriented exams. Schools approach science teaching as a product and its essence is ignored while meeting day-to-day operational challenges such as completing the syllabus, documentation or even classroom management (Eady, 2008). This has led to science being an isolated subject instead of the an inter-disciplinary inquiry it actually is. The main benefit of such an inter-disciplinary approach towards science teaching is that it can help students develop the skills of problem solving, decision-making, ethical judgment, knowledge synthesis, and planning the future. It is enormously advantageous for students to learn to treat any subject matter in a variety of ways that reinforces their thinking and problem solving skills (Kumar & Fritzer, 1994).
In Indian schools, science as a subject is further classified as physics, chemistry and biology at senior secondary level. These three subjects share various common concepts. One such concept is Potential Difference. Potential Difference is the difference in potential between two points separated in space. However, when students are taught this concept in classrooms, they are taught it within the purview of the subject. As a result, students understand potential difference in terms of the subject rather than in its entirety. For students, potential difference in physics, chemistry and biology are three different concepts. In physics it leads to the flow of current, in chemistry it leads to the movement of electrons and in biology it leads to nerve impulse.
By training, I am a life sciences student, but I have always been interested in exploring science as an integrated subject and explore topics which share an interface with other subjects such as physics and chemistry. For this article, I have chosen one such topic which students find difficult to correlate and have involved the application of the concept in all the three subjects, viz biology, chemistry and physics.
I have developed a classroom plan for teaching “Defects of Vision and their Correction in the Human Eye”. This is a subtopic from National Council of Education Research and Training (NCERT) Science book; Grade 10, chapter 11, titled “The Human Eye and the Colorful World” (NCERT, 2015).
An overview of the topic
Class: X
Chapter: 11. The human eye and the colourful world
Topic: Defects of vision and its correction
Approach: Guided inquiry through exploration of the concept
Previous knowledge required
Image formation by the eye, characteristics of the eye lens, refractive index, role of ciliary muscles, iris and cornea in processing the amount of light, the structure and shape of the lens.
The human eye and its defects was an intriguing topic for me in my school days and even until recently. I was never able to build connections between focal length, ciliary muscle and the formation of an image on the retina and various other concepts in between. For the sake of passing the exam, my school teacher had suggested a few tricks which worked really well for the kind of questions I had to answer.
However for this article, I will be treating this topic differently. I will be using a simple activity to introduce and further develop on the concepts. The topic will follow the suggested flow.
1. Concept: Focal length of the eye and how it is related to image formation on retina.
2. Change in focal length of the eye: Defects in ciliary muscles.
3. Myopia and treatment for the disease.
4. Hypermetropia and treatment for the disease.
Working model of the eye
A working model of the eye can be created easily by using a long cylindrical box (as shown in Figure 1). I used an empty box of Pringles chips. This box is open at both the ends, one end works as an observation point and the other as a source of light. Near the light source end, make a small slit for holding lenses. Make another slit in the center of the box. This could be around 20 to 30 cm in length. This will have a graded scale which will help in identifying the distance at which the image is formed. The slit will be used to hold an aperture which will be used as a proxy for the retina. Also, the movement of the retina through the graded scale will work as proxy for the ciliary muscles and will help students to understand how ciliary muscles help in contraction or dilation of the pupil to get light to converge or diverge.
You will also need lenses with focal lengths of 5 cm, 10 cm, 15 cm and so on, depending on the length of the cylinder. (While demonstrating the activity, students should not be told about the focal length of the lens. Instead they should be told to use lenses of varying widths.) Students will also be given one concave and one convex lens each to be used for eye correction along with lens holder.
A lens holder can be created by cutting out a hole in some foam (EVA Foam or EPE Foam, either can be used) in the centre equal to the size of the lens used. Once operational, this lens holder will mimic the lenses used by opticians to test vision. A similar empty holder can be used to make a working retina by pasting white paper or film across the centre of the holder so that it covers the entire hole. The width of the retina should be such that it can pass through the slit provided and its diameter must be less than the diameter of the cylinder so as to ensure smooth movement. Once this working model is ready, it can be used by students to explore the concept.
While students work on the model, the following questions can be used to probe:
- Which type of lens is present in human eye? Concave or convex. Why do you think so?
- What is the function of the ciliary muscles? What is analogous to ciliary muscles in this model?
- What is the role of the retina? Where can we locate the iris in this model? What is the function of the iris?
Focal length and image formation
Once the working model is ready, students can explore the concept of focal length and image formation. For this, students can be asked to do the following (see figure 2):
- Ask students to place the lens with medium width in the lens holder.
- Use an electric bulb or tubelight as light source and observe where the image is formed.
- Ask students to move the retina with the help of the holder. They can move the retina across the cylinder to find the best image.
- Ask students to note the distance given on the graded scale.
While students are engaged in this activity, the following questions can be asked:
- How will you justify that the focal length for this lens is 10 cm?
- How can the human eye manage to limit the amount of light entering the pupil?
- Is it possible to move the retina in the human eye as you are doing here?
- What will happen if we place a small glass filled with water between the retina and the lens? Justify your answer.
Myopia
Once all the students have understood the concept of focal length, they can be asked to replace the lens with a thicker lens. Let the students observe if there is any change in the position of the formation of the image (see figure 3). If yes, where has the image moved to? Why do you think this has happened?
After this discussion, the teacher can introduce the concept of myopia and explain what happens in a myopic eye. The teacher can ask the students about the reason for this. Further discussions can be initiated on how this condition can be treated, what type of lens will treat this condition and why.
Depending on the time, involvement of the students and the teacher’s autonomy, this inquiry can be extended by adding multiple concepts and ideas.
Hypermetropia
Students can be asked to explore this idea themselves and the teacher can check whether their inquiry is moving in the right direction or whether they need some handholding. Similar questions, as suggested above, can be asked by the teacher to probe the students (see figure 4).
Once this is done, students can be further encouraged to dive into the concept by giving various problems, both numerical and based on ray diagrams.
To complement this inquiry, teachers can use computer animations and simulation models of the human eye. These animations provide considerably more information than the still images. Simulations provide users the opportunity to manipulate with parameters and validate the results using a virtual experimentation. However, animations or simulations as an only learning tool doesn’t help students in efficient concept acquisition (Hoeling, 2011).
Works cited
- Eady, S. (2008). What Is the Purpose of Learning Science? An Analysis of Policy and Practice in the Primary School. British Journal of Educational Studies, 4-19.
- Hoeling, B. M. (2011). “Staying in Focus” – An Online Optics Tutorial on the Eye. The Physics Teacher, 86-88.
- Kumar, D., & Fritzer, P. (1994). Critical Thinking Assessment in a Science and Social Studies Context. American Secondary Education, 2-4.
- NCERT. (2015). The Human Eye and the Colorful World. In NCERT, Science (pp. 187-198). New Delhi: NCERT.
- LearNext. (n.d.). Next ScienceLab Class 10 Science CBSE – Human Eye and Defects – Activity Time. Retrieved 07 2019, from Youtube.com: https://www.youtube.com/watch?v=CX8XaBvgfAY
The author is interested in Constructive Science Pedagogy and believes in creating active learning spaces for pupils in schools by enhancing the engagement of students in the classroom learning process. His other areas of interest include Curriculum Integration, Designing Formative Assessments and Integrating Life Skills to the School Curriculum. He can be reached at santosh.sharma@apu.edu.in.
