1. Mechanical Strength of of the Cornea after Femtosecond Laser Penetrating Keratoplasty NE Knox Cartwright, 1, 2 JR Tyrer, 2 J Marshall 1 1: Ophthalmology, King’s College London; 2: Mechanical Engineering, Loughborough University

2. Financial Disclosure John Marshall is a consultant for Advanced Medical Optics

3. 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.

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

5. 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

6. 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.

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

8. Results at 1 Week Quantitative measurement was not possible from corneas with top hat and zig-zag PKs due to interface leak

9. Results at 1 Week IncisionStrain increase 135º Conical15 % * Top hat18 % * Christmas Tree20 % * Zig-square21 %* Conventional44 % Mushroom[wound leak] Zig-zag[wound leak] [*p < 0.05 compared to conventional]

10. 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

11. Contact Nathaniel KNOX CARTWRIGHT n.knoxcartwright@gmail.com