Peripheral Vision and Visual Pathways

 

Objective:

To explain in short essays or diagrams how changes in peripheral vision can be associated with damage to the retina or central neural pathways, or reflect tumors in the brain, at the level of 85% proficiency for each student.

 

In order to achieve this objective, you will need to be able to:

  1. Measure peripheral vision in two axes.
  2. Explain the anatomy of the visual pathways

Materials:

Group Supplies:

colored pencils or pens

visual field diagrams

four colors of string to represent axons

four colors of beads to represent cell bodies

Lab Supplies:

disc perimetry device and target wand

Methods and Results:

Peripheral Vision

 

  1. To test the right eye, have the subject occlude the left eye.
  2. Hold the large plastic half disc horizontally against the nose to test the temporal and nasal fields.
  3. Have the subject look at the center dot.
  4. To test the temporal field, hold the wand 1 cm to the temple side of the center dot and move outward until the peripheral target disappears. Repeat the test starting at 90o and move toward the center. Record the point of disappearance and appearance in degrees on the temporal side of the visual field diagram for the RIGHT eye.
  5. To test the nasal field, hold the wand near the center dot and move outward until the peripheral target disappears. Repeat the test starting at 90o and move toward the center. Record the point of disappearance and appearance in degrees on the nasal side of the visual field diagram for the RIGHT eye.
  6. Hold the large plastic half disc vertically against the nose to test the superior and inferior fields.
  7. To test the superior field, hold the wand near the center dot and move upward until the peripheral target disappears. Repeat the test starting at 90o and move downward to the center. Record the point of disappearance and appearance in degrees on the superior field of the visual field diagram for the RIGHT eye.
  8. To test the inferior field, hold the wand near the center dot and move downward until the peripheral target disappears. Repeat the test starting at 90o and move upward to the center. Record the point of disappearance and appearance in degrees on the inferior field of the visual field diagram for the RIGHT eye.
  9. Repeat for the LEFT eye with the right eye occluded.

Visual Field Diagram RIGHT Eye

 

Nasal Field

Temporal Field

 

 

Superior Field

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Inferior Field

 

 


Visual Field Diagram LEFT Eye

 

Nasal Field

Temporal Field

 

 

Superior Field

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Inferior Field

 

 

 


Visual Pathways

Construct the visual pathway using different colored beads and string. Include the cell bodies, axons, and synaptic sites for each pathway. Use beads to represent cell bodies and string to represent axons. Use a sheet of paper and label each nucleus and tract as they are relevant.

Use the following description, table and illustrations as a guide.

Visual pathways

Organization of the Visual Pathways

 

Left Eye

Right Eye

Left Half

Right Half

Left Half

Right Half

Left Optic Nerve

Right Optic Nerve

Optic Chiasm

Left Optic Tract

Right Optic Tract

Left Optic Tract

Right Optic Tract

Left Superior Colliculus

Left LGN

Right Superior Colliculus

RightLGN

Left Superior Colliculus

Left LGN

Right Superior Colliculus

RightLGN

Left Visual Cortex

Right Visual Cortex

Left Visual Cortex

Right Visual Cortex

 


Pathways to Primary Visual Cortex

 

 

Pathways to Superior Colliculus

 


 

Discussion:

  1. The retina extends farther forward on the medial (inside) of the eye than the lateral (outside). Did this affect the findings?
  2. Why is the superior field less than the inferior field?
  3. What accounts for the temporary target disappearance sometimes noted when testing the temporal fields?
  4. Could retinal damage be localized based on the results of this test?
  5. Think of the situation where reduced field "tunnel vision" could be dangerous.
  6. Reduced field of vision is often a symptom of glaucoma. Can you offer an explanation for this occurrence?
  7. Diagram the pathway and neurons involved from the retina to the visual cortex.
  8. Describe how the tectal system (superior colliculus) pathways are involved in the control of the extrinsic eye muscles, circular muscle fibers of the iris, and ciliary muscle.
  9. Describe the visual disturbance that often accompanies a pituitary tumor. Explain why this particular pattern is observed.
  10. If a patient reported that he could not see with his left eye, how could you tell if the problem was the optic nerve or the optic radiation? Explain.

David G. Ward, Ph.D.  Last modified by wardd 23 May, 2006