Visual Experiments
I. Identify the following:
Instruments: Example One, Example Two
II. Eye Movement, Field of vision, binocular vision, and accommodation.
For this experiment you will need a pencil, chair, and test subject.
Have the test subject sit in the chair and ask them to follow the eraser of the pencil as you move it right to left, up and down, and in circles going clockwise and counterclockwise. Record the results and note any problems. What ocular muscles are being used to move the eye in each experiment? What Cranial Nerve is responsible for signaling the muscle movement for each experiment?
Next stand behind the test subject and ask them to look straight ahead. Move the pencil from behind their head around to the side, past their ears toward the front of their face holding the pencil at least 1 foot (12 inches) away from their head. Ask them to tell you when they first see the pencil come into their peripheral vision. Repeat test for both eyes. Next have them close one eye and repeat the experiment, starting on the side with the closed eye. Record when the test subject sees the object come into view. Repeat for the other side. These two experiments test the field of vision and the overlap created by binocular vision. Do you results match what is presented in the textbooks?
Next stand in front of the test subject about two arms lengths away. Ask the subject to keep their eyes focused on the pencil eraser as you bring it closer to them, eventually touching their nose. What did you notice about their pupil size ? What did you notice about their eye position ? How do we focus on near and far objects ?
III. Visual Acuity
Print out the Snellen eye chart or make your own. Stand 30 feet from the test subject and ask them to remove any corrective lenses (contacts, glasses, etc.), close one eye, and read any line that they see clearly. Repeat with the other eye. Come 5 feet closer to the test subject and repeat the experiment at 20 feet, 15 feet, and 10 feet. Record the results. If the patient has corrective lenses (glasses or contacts) ask them to now wear them and repeat the experiment. What are some factors that affect how well a person can see? How might these be corrected?
Print out the Astigmatism chart or make your own. Ask the test subject to remove any corrective lenses and to note any lines that appear fuzzy. Repeat experiment with the corrective lenses in place. What might cause astigmatism? How might it be corrected?
IV. Color Blindness
Print out one of the Ishihara color blind charts (photo, drawing) or make your own using colored construction paper or fabric. Have the test subject identify the shape or number. Record the results. What are some of the types and causes for color blindness? Are there any treatments? If not, how do people adapt?
V. Blind Spot
Print out the blind spot drawing. Have the test subject hold the piece of paper ~18 inches away from their face. Have them close their right eye and with their left eye open, focus on the circle while slowly bringing the paper closer to their face. When the cross dissappears, that indicates the blind spot for the left eye. Record the distance of the paper from the eye. To repeat with the right eye, close the left eye and focus on the cross. Hold the paper 18 inches away and bring the paper slowly toward the face. When the circle disappears, this indicates the blind spot for the right eye. Record the distance from the right eye to the paper. Are their any differences ? What is the anatomical reference for the blind spot? When you are driving and wanting to change lanes, why is it not enough to just check your mirrors?
