title: Supersonic shear wave elastography for the in vivo evaluation of transepithelial corneal collagen cross-linking.
abstract: OBJECTIVE
  To assess corneal stiffening with supersonic shear wave imaging (SSI) technology in an experimental model of iontophoresis-assisted transepithelial corneal collagen cross-linking (I-CXL).
  
  
  METHODS
  Six rabbits underwent full, central I-CXL in one eye. The contralateral eye served as control. In vivo iontophoresis was used for 10 minutes to perform transepithelial delivery of riboflavin prior to UV-A irradiation. Accelerated UV-A protocol was applied for 9 minutes with a 10-mW/cm(2) irradiance. Animals were killed and both treated and control corneas were then immediately mounted on a corneal artificial anterior chamber and internal pressure was varied from 15 to 50 mm Hg in 5-mm Hg increments. Swelling was evaluated via central corneal thickness measurements. Ex vivo inflation tests were monitored using SSI technology that provides real-time mapping of the corneal elasticity.
  
  
  RESULTS
  Corneal yellowing of the central 9-mm diameter area was clearly visible in the iontophoresis area of all treated eyes. Elasticity versus internal pressure revealed significant differences of the change in elasticity coefficient with pressure between I-CXL-treated and control corneas with a mean slope that was 27.1 and 16.9 kPa/mm Hg, respectively (P = 0.029). Differences in elasticity at individual pressure levels between groups were statistically significant above 40 mm Hg (P < 0.05).
  
  
  CONCLUSIONS
  Intraocular pressure variations were the most important limitations for in vivo stiffness monitoring with SSI because stiffness is a function of internal pressure. Supersonic shear wave imaging succeeded in comparing corneas that underwent I-CXL by performing ex vivo inflation tests where pressure was controlled. Iontophoresis-assisted transepithelial corneal collagen cross-linking corneas exhibited increased resistance to pressure rise, indicating stiffening. In vivo I-CXL and ex vivo SSI is an interesting model to evaluate the sole effect of photopolymerization occurring in the CXL process close to physiological conditions.
authors: Ophthalmology Department, National Reference Center for Keratoconus (CRNK), Centre Hospitalier Universitaire, Bordeaux, France.
authors: David
authors: D
authors: Touboul
authors: Jean-Luc
authors: JL
authors: Gennisson
authors: Thu-Mai
authors: TM
authors: Nguyen
authors: Antoine
authors: A
authors: Robinet
authors: Cynthia J
authors: CJ
authors: Roberts
authors: Mickael
authors: M
authors: Tanter
authors: Nicolas
authors: N
authors: Grenier
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism / Q000503:physiopathology*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods*; D007640:Keratoconus / Q000378:metabolism / Q000503:physiopathology* / Q000628:therapy; D008297:Male; D011817:Rabbits
chemical_list: D003432:Cross-Linking Reagents; D003094:Collagen
keywords: biomechanics; cornea; corneal collagen cross-linking; elasticity; iontophoresis; keratoconus; riboflavin; shear wave elastography; supersonic shear wave imaging