title: Comparison of Corneal Riboflavin Gradients Using Dextran and HPMC Solutions.
abstract: OBJECTIVE
  To determine the riboflavin concentration gradient in the anterior corneal stroma when using hydroxypropyl methylcellulose (HPMC) or dextran as the carrier agent.
  
  
  METHODS
  Four different groups of porcine corneas (5 each) were compared regarding the riboflavin concentration in the anterior stroma. Prior to all experiments, stable hydration conditions were established for the corresponding solution. The dextran groups were treated with 0.1% riboflavin in 20% dextran for 10 and 30 minutes and the HPMC groups with 0.1% riboflavin in 1.1% HPMC for 10 and 30 minutes. After imbibition, nonlinear microscopy and consecutive image analysis were used to determine two-photon fluorescence intensities. To determine the riboflavin concentration, corneas were saturated and measured a second time by two-photon microscopy. With this measurement, a proper correction for absorption and scattering could be performed. Ultraviolet-A (UVA) transmission was measured after the application time for each group.
  
  
  RESULTS
  Riboflavin concentration decreased with increasing depth and increased with longer application times in all groups. Comparing the dextran for 30 minutes and HPMC for 10 minutes groups, a significantly higher stromal riboflavin concentration was found within the most anterior 70 µm in the dextran group for 30 minutes, whereas deeper than 260 µm HPMC-assisted imbibition for 10 minutes yielded higher concentrations. In dextran-treated corneas, values obtained from pachymetry were substantially reduced, whereas HPMC-assisted imbibition led to a decent swelling. UVA transmission values were higher in dextran-assisted imbibition than in HPMC-assisted imbibition.
  
  
  CONCLUSIONS
  Stromal riboflavin gradients are similar when applied in dextran for 30 minutes and HPMC for 10 minutes. When using HPMC solutions, a shallower cross-linked volume is expected due to a higher corneal hydration. [J Refract Surg. 2016;32(12):798-802.].
authors.forename: Tobias
authors.initials: T
authors.lastname: Ehmke
authors.forename: Theo G
authors.initials: TG
authors.lastname: Seiler
authors.forename: Isaak
authors.initials: I
authors.lastname: Fischinger
authors.forename: Tammo
authors.initials: T
authors.lastname: Ripken
authors.forename: Alexander
authors.initials: A
authors.lastname: Heisterkamp
authors.forename: Beatrice E
authors.initials: BE
authors.lastname: Frueh
mesh_terms: D000818:Animals; D003315:Cornea / Q000502:physiology; D063171:Corneal Pachymetry; D003319:Corneal Stroma / Q000378:metabolism*; D003432:Cross-Linking Reagents; D003911:Dextrans / Q000493:pharmacokinetics*; D004337:Drug Carriers; D065347:Hypromellose Derivatives / Q000493:pharmacokinetics*; D036641:Microscopy, Fluorescence, Multiphoton; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000493:pharmacokinetics*; D012256:Riboflavin / Q000493:pharmacokinetics*; D013552:Swine; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D003911:Dextrans; D004337:Drug Carriers; D017319:Photosensitizing Agents; D065347:Hypromellose Derivatives; D012256:Riboflavin