Biomechanical efficacy of collagen crosslinking in porcine cornea using a femtosecond laser pocket.
OBJECTIVE
The aim of this study was to assess the biomechanical efficacy of transepithelial collagen crosslinking using the femtosecond laser pocket technique compared with that using the standard crosslinking (CXL) technique.


METHODS
Forty ex vivo porcine eyes were divided into 4 groups with 10 samples each. Group 1 comprised the untreated controls. Group 2 was the standard CXL group with debridement, instillation of 0.1% riboflavin-dextran solution for 15 minutes before and every 5 minutes during the 30 minutes of irradiation with ultraviolet A (UVA) light of 370 nm and an irradiance of 3 mW/cm². Group 3 pertained to the femtolaser pocket control with an intrastromal pocket but without riboflavin/UVA. Group 4 was the femtolaser pocket CXL group with an intrastromal pocket of an 8-mm diameter at a 180-μm depth, riboflavin/dextran application for 15 minutes and subsequent exposure to UVA light for 30 minutes. Postoperatively, biomechanical stress-strain measurements were performed.


RESULTS
In the standard CXL group, the stress at 10% strain was 207.8 ± 64.1 × 10 Pa (+79.45% vs. controls; P = 0.021) compared with 115.8 ± 20.8 × 10 Pa in the untreated control group; in the crosslinked femtolaser pocket group, it was 159.5 ± 30.4 × 10 Pa (+37.74%; P = 0.049), in the non-cross-linked femtolaser pocket group, it was 103.5 ± 17.3 × 10 Pa (-10.62%; P = 0.103). The Young modulus was 5.4 MPa (+100% vs. controls) in the standard CXL group, 3.7 MPa (+37.04%) in the crosslinked femtolaser pocket group, and 2.4 MPa (-11.12%) in the non-cross-linked femtolaser pocket group compared with 2.7 MPa in the untreated control group.


CONCLUSIONS
The biomechanical effect of CXL using the femtolaser pocket technique is about 50% less pronounced than that after standard CXL. Future studies will show whether the efficacy of the technique can still be improved and whether the clinical effect is sufficient for stabilizing ectatic corneas.
*Department of Ophthalmology, AugenMVZ Lausitz, Kamenz, Germany; †Department of Anatomy II, Friedrich-Alexander University of Erlangen-Nürnberg, Erlangen, Germany; ‡Department of Ophthalmology, University of Dresden, Dresden, Germany; §WaveLight GmbH, Erlangen, Germany; and ¶Department of Ophthalmology, Ruprecht-Karls University, Heidelberg, Germany.
Gregor
G
Wollensak
Christian M
CM
Hammer
Eberhard
E
Spörl
Jörg
J
Klenke
Katrin
K
Skerl
Yao
Y
Zhang
Saadettin
S
Sel
D000818:Animals; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000502:physiology* / Q000601:surgery; D063171:Corneal Pachymetry; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D004548:Elasticity / Q000502:physiology*; D053685:Laser Therapy / Q000379:methods; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D012256:Riboflavin / Q000627:therapeutic use*; D013524:Surgical Flaps; D013552:Swine; D041623:Tomography, Optical Coherence; D014466:Ultraviolet Rays
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin