title: Corneal elasticity after oxygen enriched high intensity corneal cross linking assessed using atomic force microscopy.
abstract: The purpose of this study was to assess anterior and mid corneal stromal elasticity after high intensity (HI) corneal cross linking (CXL), with and without oxygen (O2) enrichment, and compare these results to conventional CXL. Experiments were performed on 25 pairs of human cadaver eyes, divided into four different groups. Group 1 included corneas that did not receive treatment and served as controls; Group 2 included corneas that received conventional CXL treatment (Dresden Protocol: corneal epithelial debridement, 30 min of riboflavin pretreatment followed by 30 min of exposure to 3 mW/cm2of ultraviolet light); Group 3 included corneas that received HI CXL treatment (corneal epithelial debridement, 30 min of riboflavin pretreatment followed by 3 min of exposure to 30mW/cm2of ultraviolet light); and Group 4 included corneas that received the same treatment as Group 3, except that they were enriched with oxygen (4 L per minute pure O2gas stream) during ultraviolet irradiation. In each group, corneas were subdivided to assess anterior stromal elasticity and mid stromal elasticity. Corneal stromal elasticity was quantified using Atomic Force Microscopy (AFM) through micro-indentation. Young's modulus for the anterior corneal stroma was 14.5 ± 6.0 kPa, 80.7 ± 44.6 kPa, 36.6 ± 10.5 kPa, and 30.6 ± 9.2 kPa, for groups 1, 2, 3 and 4 respectively. Young's modulus for the mid corneal stroma was 5.8 ± 2.0 kPa, 20.7 ± 4.3 kPa, 12.1 ± 4.9 kPa, and 11.7 ± 3.7 kPa, for groups 1, 2, 3 and 4, respectively. In the anterior stromal region, conventional CXL demonstrated a significantly different result from the control, whereas the two HI CXL protocols were not significantly different from the control. There were no statistical differences between the two HI CXL protocols, although only the HI CXL protocol with O2enrichment was significantly different from the conventional CXL group. In the mid stromal region, once again only conventional CXL demonstrated a significantly different result from the control. There were no statistical differences between the two HI CXL protocols, and both HI CXL protocols were significantly different from the conventional CXL group. Oxygen enriched HI CXL seems to offer similar changes in corneal elasticity when compared to HI CXL without the presence O2. Conventional CXL increases corneal stiffness more than HI CXL both with and without O2enrichment.
authors.affiliation: Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, FL, USA.
authors.forename: Vasilios F
authors.initials: VF
authors.lastname: Diakonis
authors.affiliation: Florida Lions Eye Bank, Bascom Palmer Eye Institute, University of Miami, FL, USA.
authors.forename: Nikita Y
authors.initials: NY
authors.lastname: Likht
authors.affiliation: Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, FL, USA.
authors.forename: Nilufer
authors.initials: N
authors.lastname: Yesilirmak
authors.affiliation: Florida Lions Eye Bank, Bascom Palmer Eye Institute, University of Miami, FL, USA.
authors.forename: Desiree
authors.initials: D
authors.lastname: Delgado
authors.affiliation: Pharmathen Pharmaceuticals, Athens, Greece.
authors.forename: Andreas E
authors.initials: AE
authors.lastname: Karatapanis
authors.affiliation: Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, FL, USA.
authors.forename: Yener
authors.initials: Y
authors.lastname: Yesilirmak
authors.affiliation: Diabetes Research Institute, University of Miami Miller School of Medicine, Miami, FL, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Fraker
authors.affiliation: Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, FL, USA.
authors.forename: Sonia H
authors.initials: SH
authors.lastname: Yoo
authors.affiliation: Biomedical Atomic Force Microscopy Laboratory, Department of Biomedical Engineering, University of Miami College of Engineering, Miami, FL, USA. Electronic address: nziebarth@miami.edu.
authors.forename: Noël M
authors.initials: NM
authors.lastname: Ziebarth
mesh_terms: D000328:Adult; D000368:Aged; D002102:Cadaver; D003315:Cornea / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D018625:Microscopy, Atomic Force / Q000379:methods*; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D014466:Ultraviolet Rays; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D010100:Oxygen
keywords: Atomic force microscopy; Cornea crosslinking; Corneal elasticity; Ultraviolet light