Sensory Case Study 5*:

 

A twenty-two year old female came to the College Preparatory Medical Center for evaluation for corneal transplants using cutting-edge biotechnology.   At the age seven the patient had an accident involving a flare-up of lighter fluid when lighting a barbeque grill.  The patient had second-degree burns over her hands and parts of her face.  The heat flash had damaged her vision. In the normal eye the epithelial cells of a cornea wear away through ordinary eye movements and are replaced by stem cells located in the corneal limbus.  She had essentially lost her vision with minimal light/dark recognition.  As a precocious child, she wanted to be independent, and learned how to dress, eat, play, and navigate the house.  After several years she became proficient in reading and typing Braille.  At the age of sixteen, she acquired a Seeing Eye dog and a special "blind" cane, both of which acted as surrogate eyes.  She developed a reliance on her other senses and started flourishing socially and in school, but still longed for seeing blue sky she remembered as a child.  At the age of eighteen, she had corneal transplants performed at the Head Royal University Medical School but these failed after several weeks.

 

Questions:

 

1.) Explain the mechanism of phototransduction in the eye.  Be sure to include anatomy and cellular structures within the retina.

 

2.) Why do humans have circular pupils?

 

3.) What function does a cornea have in vision?

 

4.) Can a cornea be repaired after sustaining damage?  Explain.

 

5.) What is a cornea transplant and how successful is the procedure?

 

6.) Why do some cornea transplants fail? Elaborate.

 

7.) What is a stem cell?  What is the difference between a totipotent, pluripotent, multipotent and unipotent stem cell?  How do adult and embryonic stem cells differ?

 

8.) What type of stem cell is used to reconstruct the cornea in this procedure, why are they important, and what problems have been encountered in using this type of stem cell?

 

9.) How do stem cells normally function in the cornea?

 

10.) What are some major concerns with adult vs. embryonic stem cell use?

 

*adapted from Eyes Without a Face:

Stem Cell Research and Corneal Implants

by

Kari Mergenhagen, University at Buffalo, State University of New York