Experimental in-vitro investigation on Epi-Off-Crosslinking on porcine corneas

Abstract

Aim To evaluate quantitatively the effects of the Epi-Off-CXL irradiance dose on the stromal stiffening of pig corneas. Setting Laboratory of Biological structures (LaBS), Politecnico di Milano, Milano, Italy. Methods Inflation tests have been carried on 90 excised and de-epithelized pig corneas, monitoring the change of configuration of the corneal dome at specific pressures. Test have been carried out twice on each cornea, once before and once after Epi-Off-CXL performed at a constant irradiance of 9 mW/cm2 and variable UV-A exposure times. Corneas were grouped according to the exposure time (2.5, 5, 10, 15 and 20 min), proportional to the irradiation dose (1.35, 2.7, 5.4, 8.1, and 10.8 J/cm2). A theoretical model based on linearized shell theory has been used to estimate the increment of the corneal stiffness. Results The linearized shell theory allowed to establish a quantitative relation between the increment of the stiffness parameters and the irradiation dose. Relative to the pre-treatment values, in all experiments the post-treatment corneal stiffness revealed a pronounced increase. In general, the stiffness gain increased with the exposure time. No significant differences in stiffening was observed between tests conducted at 2.5, 5, and 10 min exposure. Conclusions Qualitatively, the effectiveness of accelerated CXL treatments observed in pig corneas complies very well with in-vivo clinical results in humans, suggesting that experimental data in pigs can be very useful for the design of the procedure in humans. A larger irradiation dose provides a larger increment of the corneal stiffness. Due to the biological variability of the tissues, however, it is difficult to distinguish quantitatively the level of the reinforcement induced by accelerated protocols (low doses with < = 10 min exposure), less prone to induce damage in the corneal tissue. Therefore, the definition of personalized treatments must be related to the actual biomechanics of the cornea.

A predictive model of UV-A-riboflavin crosslinking treatment on porcine corneas

“…Interestingly, the theoretical model, supported by experimental data, revealed that the effect of CXL depends more on the duration of the irradiation than on the overall applied UV-A intensity (fluence). A recent experimental study on pressurized porcine corneas tested the stiffening effect of different irradiation time (2.5, 5, 10, 15, 20 min) of de-epithelialized corneas [10]. Results demonstrated that the duration of the irradiation has a marked effect on stromal stiffening, in agreement with the previous theoretical model.…”

“…It is well established that the stiffening effect due to CXL treatment is highly dependent on the duration of treatment and that the stiffness distribution within the cross-section is inhomogeneous. A recent numerical study attempted to provide a relationship between the stiffness depth of penetration and the treatment duration [13], by making use of the experimental data presented in [10]. To limit the introduction of arbitrary fitting coefficients, the through-thickness CXL stiffening of the cornea was assumed as piece-wise-constant.…”

Transepithelial Enhanced Fluence Pulsed Light M Accelerated Crosslinking for Early Progressive Keratoconus with Chemically Enhanced Riboflavin Solutions and Air Room Oxygen

“…The finite element analysis provided at increasing irradiation doses proved that the increase in the cross-link density at a comparatively high value of irradiation dose could help improve the material strength, thus increasing the fluence not only provides an increased depth in the demarcation lines, but an increased cornea resistance that is crucial in Epi-On treatments. These clinical and experimental observations confirmed that the way to go for Epi-On CXL treatments is to find a balance between the riboflavin concentration and higher fluence between 8.1 and 10.8 J/cm 2 [ 30 , 31 , 32 , 33 ].…”

Evaluation of the Physiological Corneal Intrastromal Riboflavin Concentration and the Corneal Elastic Modulus After Violet Light Irradiation

“…In contrast, post-CXL tests are characterized by low to moderate dispersion around the average. 26 The discrepancy may be attributed to the differences in irradiance of VL in the KeraVio procedure (0.31 mW/cm 2 for 4.8 hours). Long-term irradiation of VL on the cornea can induce degradation over time in an ex vivo porcine eye model.…”