title: Analysis of the effective dose of ultraviolet light in corneal cross-linking.
abstract: OBJECTIVE
  To analyze the efficacy of ultraviolet (UV) light initiating corneal cross-linking (CXL).
  
  
  METHODS
  The time-dependent absorption of UV light due to the depletion of the initiator (riboflavin) was calculated. The effective dose of CXL with corneal surface covered by a thin layer of riboflavin was derived analytically. The cross linking time was calculated by the depletion level of the riboflavin concentration. A comprehensive method was used to derive analytic formulas.
  
  
  RESULTS
  The effective dose of CXL was reduced by a factor (R) which was proportional to the thickness (d) and concentrations (C0) of the riboflavin surface layer. Our calculations showed that the conventional dose of 5.4 J/cm(2) had a reduced effective dose of 4.3 and 3.45 J/cm(2), for d was 100 and 200 µm, respectively, and C0=0.1%. The surface cross linking time was calculated to be T*=10.75s, for a depletion level of 0.135 and UV initial intensity of 30 mW/cm(2). The volume T* was exponentially increasing and proportional to exp (bdC0), with b being the steady state absorption coefficient.
  
  
  CONCLUSIONS
  The effective dose of CXL is reduced by a factor proportional to the thickness and concentrations of the riboflavin surface layer. The wasted dose should be avoided by washing out the extra riboflavin surface layer prior to the UV light exposure.
authors: Department of Ophthalmology, Shandong Provincial Hospital, Shandong University, Jinan 250021, Shandong Province, China.
authors: Yong
authors: Y
authors: Zhang
authors: Department of Electronic Engineering, Taiwan University, Taipei, Taiwan 101, China.
authors: Kuan-Chen
authors: KC
authors: Wang
authors: Nobel Eye Institute, Taipei, Taiwan 101, China.
authors: Chao-Kai
authors: CK
authors: Chang
authors: New Vision Inc., Taipei, Taiwan 103 and Gong-Rui Medical Technology Corp, Xiamen, Fujian Province, China.
authors: Jui-Teng
authors: JT
authors: Lin
keywords: collagen corneal cross-linking; keratoconus; riboflavin; safety efficacy; ultraviolet radiation