title: High-irradiance CXL combined with myopic LASIK: flap and residual stroma biomechanical properties studied ex-vivo.
abstract: OBJECTIVE
  To evaluate ex vivo biomechanical and enzymatic digestion resistance differences between standard myopic laser in-situ keratomileusis (LASIK) compared with LASIK+CXL, in which high-irradiance cross-linking (CXL) is added.
  
  
  METHODS
  Eight human donor corneas were subjected to femtosecond-assisted myopic LASIK. Group A (n=4) served as a control group (no CXL). The corneas in LASIK+CXL group B were subjected to concurrent prophylactic high-irradiance CXL (n=4). Saline-diluted (0.10%) riboflavin was instilled on the stroma, subsequently irradiated with UV-A through the repositioned flap. The cornea stroma and flap specimens were separately subjected to transverse biaxial resistance measurements; biomechanical differences were assessed via stress and Young's shear modulus. Subsequently, the specimens were subjected to enzymatic degradation.
  
  
  RESULTS
  For the corneal stroma specimen, stress at 10% strain was 128±11 kPa for control group A versus 293±20 kPa for the LASIK+CXL group B (relative difference Δ=+129%, p<0.05). The stress in group B was also increased at 20% strain by +68% (p<0.05). Shear modulus in group B was increased at 10% strain by +79%, and at 20% strain by +48% (both statistically significant, p<0.05). The enzymatic degradation time to dissolution was 157.5±15.0 min in group A versus 186.25±7.5 min in group B (Δ=+18%, p=0.014). For the flaps, both biomechanical, as well as enzymatic degradation tests showed no significant differences.
  
  
  CONCLUSIONS
  LASIK+CXL appears to provide significant increase in underlying corneal stromal rigidity, up to +130%. Additionally, there is significant relevant enzymatic digestion resistance confirmatory to the above. LASIK flaps appear unaffected biomechanically by the LASIK+CXL procedure, suggesting effective CXL just under the flap.
authors: Laservision.gr Eye Institute, Athens, Greece Department of Ophthalmology, New York University Medical School, New York, New York, USA.
authors: Anastasios John
authors: AJ
authors: Kanellopoulos
authors: Laservision.gr Eye Institute, Athens, Greece.
authors: George
authors: http://orcid.org/0000-0002-9620-3878
authors: G
authors: Asimellis
authors: Department of Cornea & Refractive Surgery, Harvard Medical School, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts, USA.
authors: Borja
authors: B
authors: Salvador-Culla
authors: Department of Cornea & Refractive Surgery, Harvard Medical School, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts, USA.
authors: James
authors: J
authors: Chodosh
authors: Department of Cornea & Refractive Surgery, Harvard Medical School, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts, USA.
authors: Joseph B
authors: JB
authors: Ciolino
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D003131:Combined Modality Therapy; D003315:Cornea / Q000187:drug effects / Q000601:surgery; D003319:Corneal Stroma / Q000502:physiology*; D003432:Cross-Linking Reagents; D004548:Elasticity / Q000502:physiology; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000188:drug therapy / Q000601:surgery / Q000628:therapy*; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D012256:Riboflavin / Q000627:therapeutic use; D013524:Surgical Flaps / Q000502:physiology*; D014019:Tissue Donors; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D012256:Riboflavin
keywords: Biochemistry; Cornea; Eye (Tissue) Banking; Treatment Lasers; Treatment Surgery