Mechanical Strength of of the Cornea after Femtosecond Laser Penetrating Keratoplasty NE Knox...

Mechanical Strength of of the Cornea after Femtosecond

Laser Penetrating Keratoplasty

NE Knox Cartwright,1, 2 JR Tyrer,2 J Marshall1

1: Ophthalmology, King’s College London;

2: Mechanical Engineering, Loughborough University

Financial Disclosure

• John Marshall is a consultant for Advanced Medical Optics

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.

Aim

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

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

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.

ConventionalConventional Christmas treeChristmas tree

ScarfScarfZig-squareZig-square

Strain Change at 1 Week

Strain

Results at 1 Week

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

Results at 1 Week

Incision Strain increase135º Conical 15 % *Top hat 18 % *Christmas Tree 20 % *Zig-square 21 % * Conventional 44 %Mushroom [wound leak]Zig-zag [wound leak]

[*p < 0.05 compared to conventional]

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

Contact

Nathaniel KNOX CARTWRIGHTn.knoxcartwright@gmail.com