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Some Riddles in the Microscopic Structure of the Stroma

David Maurice

Columbia University Department of Ophthalmology
Presented at
The XIII International Congress for Eye Research, Paris, France - July 26-31, 1998

Published in Journal of Refractive Surgery 
The mammalian cornea differs from other connective tissues in three ways. 
  Fine fibrils 
  Fibrillar order:  Interfibrillar forces. 
  Interfibrillar  forces. 
  Not interwoven:  Lamellar structure. 
  Not interwoven:  Lamellar structure. 
 Four puzzling features of the lamellar structure are discussed:
          1. Number of lamellae
          2. What holds them together
          3. Structural basis for high shear
          4. Architecture of lamellar waves.
  Slide 1. Cross-section of beef cornea observed under polarizing microscope. About 70 lamellae.
Slide 2. Low power TEM of beef stroma, showing 3-400 lamellae. 
  In human, Bowman describes 60 lamellae by histology, but Pouliquen et al. 307 lamellae by TEM.
  Slide 3. Small piece of stroma lying flat at bottom of cuvette under saline, and observed by slit lamp. Slit vertical, i.e., perpendicular to plane of cornea.
Slide 4. Striated appearance of very swollen stroma viewed in slit lamp as in Slide 3.
Slide 5. Showing how cohesive structures  in stroma must be stretched to several times their length by swelling and even more by shear.
Slide 6. Method of marking stroma to demonstrate shear.
Slide 7. 
 Left, unstressed. 
 Right, maximal shear.
Slide 8. 
 Left, unstressed. 
 Right, maximal shear. 

Tissue shows greater freedom of movement as hydration increases.

Slide 9. 
 Left, unstressed. 
 Right, maximal shear. 

Tissue stiffening again near maximum hydration

Slide 10. Thick cross-section of swollen stroma crushed perpendicular to face of section, showing further (irreversible) extension of structure. 
Pouliquen et al.

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