Abstract
Purpose: :
To compare the change in biomechanical properties of human cadaver corneas after standard transepithelial cross-linking (CXL-TE) versus CXL-TE using iontophoresis, different solutions and UV-A power.
Methods: :
Twelve human cadaver corneas were divided in 4 different groups according to methods of impregnations and UV-A power used: Group A (three corneas, treated with CXL-TE using an irradiance power of 3 mW/cm2 for 30 minutes and riboflavin solution with 15 % dextrane and Tromethamine); Group B (three corneas treated with CXL-TE using an irradiance power of 3 mW/cm2 for 30 minutes and riboflavin solution with Tromethamine); Group C (three corneas treated with CXL-TE using an irradiance power of 10 mW/cm2 for 10 minutes and riboflavin solution with Tromethamine); Group D (three corneas treated with an irradiance power of 10 mW/cm2 for 10 minutes, the impregnation was obtained with the aid of iontophoresis and a riboflavin solution with Tromethamine). After cross- linking, static stress-strain measurements of the corneas were performed using a microcomputer-controlled biomaterial tester with a pre-stress of 5x103 Pa. Stress stain curves were fitted with an exponential function and the Young's modulus was calculated. Thickness of the cornea was measured with an ultrasound pachymeter.
Results: :
Stress strain measurement showed an increase in corneal rigidity after cross-linking compared to standard CXL-TE, indicated by a rise in strain and in Young’s modulus calculated at 10% strain. Considering group A as standard of comparison, group B showed an increase by a factor of 1.45, group C by a factor of 1.26, group D by a factor of 1.81. Mean corneal thickness was: 627 µm for group A, 628 µm for group B, 527 µm for group C, 665 µm for group D.
Conclusions: :
CXL-TE is able to increase mechanical rigidity in human corneas in selected groups. Stress strain results showed a maximal effect in the iontophoresis group, probably due to the increased riboflavin concentration in the stroma. Stress strain measurement in the other groups showed a better results using riboflavin solution without dextrane and 3 mW/cm2 of irradiance power.
Keywords: cornea: basic science • keratoconus • clinical laboratory testing