title: A Comparison of Different Corneal Iontophoresis Protocols for Promoting Transepithelial Riboflavin Penetration.
abstract: OBJECTIVE
  To measure corneal riboflavin penetration using different transepithelial iontophoresis protocols.
  
  
  METHODS
  Freshly enucleated rabbit eyes were divided into nine treatment groups of 4 eyes. One group, in which 0.1% wt/vol riboflavin was applied for 30 minutes without iontophoresis after corneal epithelial debridement, acted as a control. The remaining groups were treated with an intact epithelium using different riboflavin formulations and varying iontophoresis current, soak, and rinse times. After riboflavin application, eyes were snap frozen in liquid nitrogen. Corneal cross sections 35 μm thick were then imaged immediately by two-photon fluorescence microscopy, using image processing software to quantify stromal riboflavin concentration at different corneal depths.
  
  
  RESULTS
  In the epithelium-on iontophoresis treatment groups, greater stromal riboflavin penetration was achieved with higher-concentration riboflavin solutions, greater iontophoresis dosage, and longer solution contact times. A protocol utilizing 0.25% wt/vol riboflavin with benzalkonium chloride (BAC) 0.01% and two cycles of applied current and subsequent soaking (1 mA 5 minutes, soak 5 minutes; 0.5 mA 5 minutes, soak 5 minutes) achieved similar stromal riboflavin penetration to epithelium-off controls. The best-performing non-BAC-containing protocol produced stromal riboflavin penetration approximately 60% that of epithelium-off controls. Riboflavin solutions containing saline resulted in minimal stromal penetration. Riboflavin loading within the epithelium was equivalent to or higher than that in the subjacent stroma, despite rinsing the ocular surface with balanced salt solution.
  
  
  CONCLUSIONS
  Modified iontophoresis protocols can significantly improve transepithelial riboflavin penetration in experimental corneal collagen cross-linking.
authors.affiliation: Moorfields Eye Hospital London, United Kingdom.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Gore
authors.affiliation: Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.
authors.forename: David P
authors.initials: DP
authors.lastname: O'Brart
authors.affiliation: Department of Physics, Imperial College London, South Kensington, London, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: French
authors.affiliation: Department of Physics, Imperial College London, South Kensington, London, United Kingdom 4Centre for Histopathology, Imperial College London, London, United Kingdom.
authors.forename: Chris
authors.initials: C
authors.lastname: Dunsby
authors.affiliation: Moorfields Eye Hospital London, United Kingdom.
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Allan
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D019573:Epithelium, Corneal / Q000378:metabolism* / Q000473:pathology; D007478:Iontophoresis / Q000379:methods*; D007640:Keratoconus / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008856:Microscopy, Fluorescence; D009883:Ophthalmic Solutions; D011817:Rabbits; D012256:Riboflavin / Q000008:administration & dosage / Q000493:pharmacokinetics*; D014803:Vitamin B Complex / Q000008:administration & dosage / Q000493:pharmacokinetics
chemical_list: D009883:Ophthalmic Solutions; D014803:Vitamin B Complex; D012256:Riboflavin