Introduction: (Initial Observation)
How does the human eye see? How does the eyeball work? Why do some people have better eyesight than others? Why do some people need glasses? Why do some people need them for distance and some need them for reading? How do optical illusions trick your eyes into seeing things you’re not? These are all interesting questions related to the human eye.
Information Gathering:
Find out about human eye. Read books, magazines or ask professionals who might know in order to learn how do the eyes work. Keep track of where you got your information from.
Following are samples of information that you may find:
The human eye is the organ which gives us the sense of sight. It consists of a ball with a lens in one side and vision cells on the other side. The lens forms an image on the vision cells and vision cells transfer that to the brain. Eyeball works like a camera. Following are more specific details on how do the eyes and the process of vision work.
process of vision
Light waves from an object (such as a tree) enter the eye first through the clear cornea and then through the pupil, the circular aperture (opening) in the iris.
The light waves are converged first by the cornea, and then further by the crystalline lens, to a nodal point (N) located immediately behind the back surface of the lens. At that point, the image becomes inverted (turned upside-down).
The light progresses through the gelatinous vitreous humor and, ideally, back to a clear focus on the retina, the central area of which is the macula. (If the eye is considered to be a type of camera, the retina is equivalent to the film inside the camera, registering the tiny photons of light which interact with it.) In the retina, light impulses are changed into electrical signals and then sent along the optic nerve and back, along the visual pathway, to the brain, which interprets these electrical signals as visual images.
Actually, then, we do not “see” with our eyes but, rather, with our brains. Our eyes merely are the beginnings of the visual process.
Vocabulary
Cornea – the clear, curved portion of the eyeball directly over the iris and pupil. Cornea is a transparent dome which serves as the outer window of the eye
iris – the colored portion of the eye that opens and closes the pupil in response to light intensity
lens – the flexible, clear, lentil-shaped object just behind the pupil
optic nerve – the nerve in the back of the eyeball that carries impulses from the retina to the brain for interpretation
pupil – the hole in the center of the iris through which light enters the eye. When the light entering the eyes is bright, the pupils will constrict (get smaller) to adjust the amount of light on retina.
retina – the light-sensitive layer of the eye that registers the image entering through the pupil; the sharpest vision comes from the macula portion of the retina
rods and cones – vision cells; rods see only black and white and are most useful for night vision; cones see only color and do best in good light
sclera – the white, outer part of the eyeball
How do cataracts effect your vision?
A cataract is a clouding of the lens in the eye that affects vision. Most cataracts are related to aging. Cataracts are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery.
Background Information
Look around. What do you see? Human beings can obtain a large amount of information about the surrounding environment through their sense of vision. But to see, we need light and the light-processing organs called eyeballs.
The outside of an eyeball is white, except for the clear, bulging cornea in front. Just behind the cornea is the iris, a colored area with a hole in the center called the pupil. Circular muscle tissue in the iris allows it to open and close the pupil to regulate the amount of light that gets inside the eyeball. Just behind the iris and pupil is the lens. The cornea and the lens work together to focus images on the retina, the light-sensitive layer that lines the inside of the eyeball.
Light moves in straight lines. Whenever a light ray encounters a surface of a different transparent medium, however, it bends (refracts) and heads off in another direction. The amount of bending depends on the nature of the transparent substance, the angle at which the light hits the surface, and the color of the light. On a curved surface such as a lens, parallel rays of light will hit the surface at different angles and will be bent differently. A greater curvature will lead to a greater difference in the amount of bending.
When your eye focuses on an object, all the light rays from a single point on that object are bent toward a single point on your retina. In the eyeball, light rays passing through the cornea are bent by its curvature toward the pupil. The lens flexes to change its curvature and finish the focusing process. Interestingly, the image projected on the retina is upside down because of the way the rays of light are bent by a double-convex lens.
On the retina are two kinds of cells that change light into nerve impulses. Rod cells do not see color but are best for night viewing because they react to very low light levels. Cone cells are for color viewing. They work best in good light and are found mostly in the center of the retina, an area called the macula, which provides the sharpest vision. Within each eye is a small blind spot with no rods or cones, where the optic nerve is attached to the eyeball. The optic nerve collects the nerve impulses and carries them to the brain, which interprets them as an image.
Need a model of the eye?
You can make a model of the eye as described in project number 24 in the list of primary projects, or you can purchase a model of the eye from science suppliers. The model shown in the right is available in MiniScience.com and klk.com.
Why do some people need them for distance and some need them for reading?
If the lens is not able to focus images on the retina, then you need a corrective lens (eyeglasses) to correct this problem. Some eyes have problem to focus the image of far objects. Such eyes are called near sighted. Some other eyes have problem to focus the image of near objects. These are called far sighted.
Far sighted and near sighted eyes need two different types of lens for correction.
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to understand how the human eye works.
Hypothesis:
Based on your gathered information, make an educated guess about any of your questions. Hypothesis must be testable by experiments.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1:
Stereogram is an image or diagram that can give a 3D impression. In this experiment you will draw a simple stereogram.
Materials:
- Paper
- Pencil
Procedure:
1.) Draw two identical rectangles next to each other.
2.) Draw a small circle in the center of the one on the left.
3.) Draw an identical circle slightly to the left of center in the rectangle on the right.
4.) Hold the paper at arm’s length or tape it to the wall and cross your eyes slightly so that the two squares exactly overlap. The circle will appear to float above the paper. See if you can construct more complex three-dimensional pictures.
Experiment 2:
As an object approaches, the human eye’s lens flexes to focus on it. Eventually the object gets so close, however, that the lens can no longer focus on it. Then the object begins to blur. How close can you bring an object before it looks blurry? Does this distance vary for different people or age groups? Does the shape or color of the object make any difference? Does it matter how brightly the object is illuminate.
Materials:
- a 2.5-cm x 5-cm (1″x 2″) swatch of printed words from a newspaper or magazine
- modeling clay or sculpting compound
- a 3″ x 5″ index card
- a cloth or soft vinyl tape measure like those used in sewing
Procedure:
1. Glue or paste the newspaper or magazine selection in the center of the 3″ x 5″ card.
2. Roll the clay into a 5-cm (2″) ball and mount the 3″ x 5″ card in it.
3. For the first test, have the test subject cover one eye with a hand.
4. Slowly bring the clay ball and words directly toward the test subject’s uncovered eye. The test subject should try to focus on the words.
5. The test subject should say “stop” when she or he can no longer focus clearly on the words. Stop moving the ball at that point.
6. Have the test subject hold one end of the tape measure to her or his cheekbone just below the eye and measure the distance to the 3″ x 5″ card. (NOTE: Having the test subjects measure the distances helps ensure that no eyes get poked.)
7. Write down the measurement. Be sure to include whether or not the test subject wears glasses or contact lenses.
8. Repeat the test several times, using different test subjects and testing different variables. For example, try the test with both eyes uncovered, with and without glasses, with different amounts of light, and so on. Just remember to change only one variable for each test and to repeat each test at least once. Average the results of repeated tests.
Experiment 3: Show how do images form inside the eyes
Introduction: Inside the human eye, an upside down image of our surroundings is formed. This image is right on the area covered with vision cells. In this experiment you will form such an image on the wall.
Procedure:
In a low light room light up a candle and place it in about 2 feet from a plan wall. If the wall has decorative paint or wall paper, hang a white paper on the wall.
Hold a magnifying glass lens between the candle and the wall in a way that the light from the candle can pass through the lens and hit the wall.
Gradually move the lens closer to the wall until you focus a clear upside down image of the candle on the wall.
While holding the lens at that position ask someone to bring the candle closer. What happens to the image? Does it lose its focus? What do you need to do to bring the image to focus again?
Experiment 4: How does the color of a text affect the maximum distance in which the text is readable?
Introduction: We can write and read text in many colors. What is the best color for writings that are far from us? Does the color of text affect the readability distance?
Define variables: The independent variable (also known as manipulated variable) is the color of the text. The dependent variable (also known as responding variable) is maximum readability distance.
Materials:
You will need a color printer and a measuring tape for this experiment.
Procedure:
- In the middle of a blank letter size paper print 8 capital letters in black color. Use Arial Black font style and size 14 fonts.
- Repeat the above with all other colors you want to test. Use a different set of letters in each paper. At the end you will have one paper for each color text.
- Mount the papers (one at a time) on a wall about 50 feet away from the subject.
- Ask the subject to walk toward the writing slowly and stop as soon as he or she can read the text. Measure and record the reading distance.
- Repeat this test with at least 3 different persons. Record your results in a table like this:
| Text Color | Max. Distance 1 | Max. Distance 2 | Max. Distance 3 | Average |
| Yellow | ||||
| Red | ||||
| Green | ||||
| Blue | ||||
| Black |
Calculate the average of Max. Distance 1, Max. Distance 2 and Max. Distance 3 for each color and write them in the last column of the results table.
Make a graph:
Make a graph to visually present your results. Use one vertical bar for each text color. The height of the bar will represent the maximum readability distance.
Optical illusions: How do optical illusions trick your eyes into seeing things you’re not?
The final step of seeing or comprehending an image happens in the mind. That is where most optical illusions happen. See the following link for some examples of optical illusions.
Materials and Equipment:
List of material can be extracted from the experiments section.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
References:
Visit your local library and find some books about anatomy and human eyes. Also visit the following link for some good information.
This is a sample of a stereograph
