1. Influence of UVA-Riboflavin corneal collagen cross-linking on biomechanical properties of keratoconic eyes
David Zadok MD, Yakov Goldich MD,
Yaniv Barkana MD, Adi Rasko MD, Isaac Avni MD
Department of Ophthalmology
Assaf Harofeh Medical Center
Israel
The authors have no conflicts of interest and no financial interest in the article’s subject matter or methods mentioned.

2. Background
Corneal Collagen-Cross linking (CXL) using UVA and Riboflavin was proposed recently as treatment to stop progression of keratoconus1
A suggested mechanism is stiffening of the cornea2
1.Wollensak G. et al, Riboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol May;135(5):620-7.
2.Kohlhaas M. et al, Biomechanical evidence of the distribution of cross-links in corneas treated with riboflavin and ultraviolet A light. J Cataract Refract Surg Feb;32(2):

3. Background
The Ocular Response Analyzer (ORA; Reichert Inc) provides in vivo measurements of corneal biomechanical properties, namely corneal hysteresis (CH) and corneal resistance factor (CRF), and non contact measurements of IOP: Goldmann correlated IOP (IOPg) and corneal compensated IOP (IOPcc)

4. Purpose
To assess changes in biomechanical properties of human corneas following treatment of keratoconus with UVA-Riboflavin CXL

5. Methods
Ten eyes of 10 patients aged 26.5±5.7 years were treated with CXL and assessed with the ORA
Inclusion criteria
progressive keratoconus documented clinically ( Astigmatic refraction and/or topography) within the past 12 months
Age >18 years
Absence of corneal opacities
No previous ocular surgeries
Minimum corneal thickness > 400 μm
No wearing of rigid contact lenses for 1 month before initial evaluation

6. Methods
Treatment: corneal deepithelization, instillation of 0.1% riboflavin in 20% dextran solution every 5 minutes for 40 minutes and corneal irradiation with UVA 3 mW/cm2 for 30 minutes
Patients were assessed before, 1week, 1month and 3 months after treatment. Comparison of postoperative to preoperative measurements was done

7. Results
CH and CRF were transiently elevated after cross-linking treatment, without statistical significance.
IOPcc and IOPg were statistically significantly higher at 1 week and 1 month.
The results presented in table and box and whisker plots (smallest, median and largest values with interquartile range) showing values before treatment (Preop) and on 1 week, 1 month and 3 months thereafter.

8. Results

9. Results

10. Results

11. Discussion
Previous in vitro studies showed increased corneal rigidity after CXL treatment using biomechanical stress-strain measurements3
In this study there were no significant changes in biomechanical properties of human corneas as measured in vivo by ORA following CXL treatment. CH and CRF were transiently elevated 1 week after treatment, but without statistical significance
IOPcc and IOPg were statistically significantly higher at 1 week and 1 month
ORA-measured IOP changes may be a measurement artifact following changes in ocular characteristics (like increased corneal thickness), and not a real IOP elevation .
3.Wollensak G. et al, Stress-strain measurements of human and porcine corneas after riboflavin-ultraviolet-A-induced cross-linking. J Cataract Refract Surg Sep;29(9):

12. Conclusions
There were no differences in corneal biomechanical properties as measured with the Ocular Response Analyzer following corneal collagen cross-linking in keratoconus
Correspondence: David Zadok MD