SUPERHUMANS & BIONICS: Electronic Eyes
Leonard Perra hasn't seen his children in ten years. He has never seen his grandson's face. An eye disease called macular degeneration has destroyed part of his sight, so a dark or empty area appears in the center of his vision. An experimental pair of goggles developed by the Baltimore VA hospital and the Wilmer Eye Institute of Johns Hopkins University may enhance Perra's remaining vision so he can see the faces of his family. Frontiers is on the scene when he tries on his electronic eyes for the first time.
Notes & Discussion
Activity: Faulty Vision
For Further Thought
Report From the Field: Joan Stelmack, Chief of Optometry, Hines Veterans Affairs Hospital
NOTES & DISCUSSION
- Review the anatomy of the eye and the physiology of vision. If the human eye is considered a camera, then the retina is the photographic film that receives the images coming through the lens. The macula sits at the back of the eye in the center of the retina, the light-sensing nerve tissue that lines the back of the eye. All parts of the retina contribute to sight, but only the macula provides sharp, central vision.
- The macula -- a tiny area 5mm in diameter -- is the point on the retina where the light rays meet as they are focused by the cornea and the lens. If the macula is damaged, the central part of the images is blocked out. Vision is distorted or reduced.
- Consider Leonard Perra's plight. The electronic goggles are a prototype and must be returned to the lab. With the goggles, Leonard Perra sees better than he has in ten years, but this enhancement of his remaining sight is only temporary -- his vision will still be affected by the disease. Have students imagine the impact of this realization.
- The scenes on Frontiers that demonstrate how someone with macular degeneration actually sees the world required a three-step process and some fancy post-production work in the editing room. First, scenes were shot normally. Then they were overlaid with another image; an irregular shape in the center represented the black area of lost central vision. Finally, another machine broke the image down into small squares called pixels. You can do this on your computer screen by enlarging an image or an individual word or letter many times until you see the block-like arrangement of individual pixels that make up the image.
ACTIVITY: FAULTY VISION
This modeling activity demonstrates the difference between a healthy eye and an eye affected by macular degeneration.
Build two models of the eye: the first demonstrates a healthy eye; the second lets you see for yourself what a person with macular degeneration experiences.
- large paper cup
- rubber band
- aluminum foil
- wax paper
- black wax marking pencil
- If you have a cross-section illustration of the eye in one of your science books, that might be a helpful reference.
- The size of the pinhole in the cup will affect the sharpness of the projected image. Although the smallest pinhole will produce the sharpest image, the image may be too dim to detect.
- Use sturdy paper cups; if too flimsy, they'll collapse.
- Dim the room as much as possible, so you have a strong contrast in brightness between the light source and the viewer's environment.
A. MODELING A HEALTHY EYE
- Use a sharp object to cut or punch a small hole in the bottom of a paper cup near the center.
- Cut a small piece of foil about 3 cm square and tape it over the hole.
- Use the pin to punch a hole in the center of the foil. The pinhole should align with the larger hole in the paper cup.
- Cut a square of wax paper about 5 inches (12.7 cm) on each side.
- Stretch the wax paper over the open end of the cup. Secure it with a rubber band so that the paper resembles a drum head.
- Darken the classroom. Aim the pinhole at a bright light source or open window. What do you see on the wax paper?
B. MODELING MACULAR DEGENERATION
- Cut another square of wax paper about 5 inches (12.7 cm) on each side.
- Color in the center of this square with the marking pencil.
- Crumple the paper to produce fold marks and scratches on the wax.
- Replace the wax paper in the original model with this sheet.
- Retry the pinhole viewer. How does this new image differ from the original one?
C. MORE ABOUT MODELS
As representations, models can teach us more about an object, concept or relationship. Sometimes models are sketched on paper. Other modeling can be done on computers. When making a model, it's important to know what each feature represents. It's also important to know the limits of the model. Otherwise, you might make predictions based upon incorrect relationships.
Match the part of the model with the part of the eye it represents.
|_____ 1. retina
||a. blackened wax paper
|_____ 2. iris
||b. aluminum foil
|_____ 3. pupil
||c. not represented on model
|_____ 4. lens
||d. wax paper
|_____ 5. macular degeneration
||e. pin hole
A: 6. upside-down image of light source or window
B: 5. no image can be seen in the center
C: 1. d, 2. b, 3. e, 4. c, 5. a
FOR FURTHER THOUGHT
- Describe the image projected onto the wax paper. How does this illustrate a person's vision?
- How does the brightness of the light source affect your observations?
- How did this activity model macular degeneration?
- The image is upside down, just as images projected onto the back of the retina are upside down, then rearranged by the brain.
- The brighter the source, the brighter the projected image.
- The crumpled and blackened wax paper represents a diseased retina. The image projected onto this retina was difficult to observe.
CREDIT: Workshop presenter and textbook author Michael DiSpezio. who contributed this activity and "Making Strides," is a science specialist based in Cape Cod, Massachusetts.
REPORT FROM THE FIELD: Joan Stelmack, Chief of Optometry, Hines Veterans Affairs Hospital
When you see a person with a white cane, what does it mean to you? To most of us it suggests someone who cannot see, so we'd be very surprised if that person could read a newspaper or see a traffic sign from two blocks away. Dr. Joan Stelmack, seen on Frontiers, explains how an apparently blind person does this. "A person may be legally blind, but he or she may not be totally blind." The diagnosis of legal blindness is given to persons with severely impaired central vision loss or the loss of peripheral vision that results in tunnel vision. "The effect of tunnel vision, "she says, "is like looking through a tube. You might able to read a newspaper or see a sign without glasses, but when you want to cross a street you'd have a very serious problem because you couldn't scan your eyes fast enough to see the cars."
On a typical day at the hospital, Dr. Stelmack evaluates and diagnoses patients, prescribes their treatment plans, provides clinical direction for her staff, conducts research and works with new devices like the goggles she fits for Mr. Perra on Frontiers. "The Hines VA Hospital uses a team approach to help legally blind and low-vision patients," explains Dr. Stelmack. Each receives individualized and specialized care from many professionals, including optometrists, nurses, physicians, social workers, psychologists and blind rehabilitation instructors.
She and her team share a common goal: to provide comprehensive care and to restore hope, respect and independence to patients who often feel hopeless about their future when confronted with vision loss. For more information about low vision, Dr. Stelmack suggests this resource: Low Vision Section, American Optometric Association, 243 N. Lindbergh Boulevard, St. Louis, MO 63141.
Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.