Mechanical%20Strength%20of%20of%20the%20Cornea%20after%20Femtosecond%20Laser%20Penetrating%20Keratoplasty

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Mechanical Strength of of the Cornea after
Femtosecond Laser Penetrating Keratoplasty

• NE Knox Cartwright,1, 2 JR Tyrer,2 J Marshall1
• 1 Ophthalmology, Kings College London
• 2 Mechanical Engineering, Loughborough University

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Financial Disclosure

• John Marshall is a consultant for Advanced
  Medical Optics

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Background

• The cornea has limited wound healing capacity
  resulting in an 4 incidence of
  post-keratoplasty wound dehiscence.
• Certain femtosecond lasers now have FDA approval
  for use in PK and the limited data available
  suggests that some of the complex incision
  profiles possible may be superior to conventional
  parallel sided trephinations.

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Aim

• To compare quantitatively the biomechanical
  differences between differing femtosecond
  penetrating keratoplasty cut configurations.

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Method

• Human eyebank corneas were obtained and
  transferred into a previously described organ
  culture model

• All surgery was performed using a 60 kHz
  Intralase femtosecond laser

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Strain Measurements

• A custom built radial shearing speckle
  interferometer was used to measure the change in
  corneal strain following an increase in
  intraocular pressure from 15.0 to 15.5 mmHg
  before, after and one week following surgery.

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Strain Change at 1 Week
Conventional
Christmas tree
Strain
Zig-square
Scarf
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Results at 1 Week

• Quantitative measurement was not possible from
  corneas with top hat and zig-zag PKs due to
  interface leak

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Results at 1 Week

• Incision Strain increase
• 135º Conical 15
• Top hat 18
• Christmas Tree 20
• Zig-square 21
• Conventional 44
• Mushroom wound leak
• Zig-zag wound leak
• p lt 0.05 compared to
  conventional

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Conclusions

• PK incisions with greater endothelial than
  epithelial diameter (top hat, scarf, zig-square,
  Christmas tree) are mechanically superior to
  conventional incisions
• Trephinations with greater epithelial than
  endothelial diameter (mushroom and zig-zag) are
  biomechanically inferior to parallel sided
  incisions

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Contact

• Nathaniel KNOX CARTWRIGHT
• n.knoxcartwright_at_gmail.com