How does atmospheric pressure cold helium plasma affect the biomechanical behaviour on alkali-lesioned corneas?

Abstract Background - Melting corneal ulcers are a serious condition that affects a great number of animals and people in the world and it is characterised by a progressive weakening of the tissue leading to possible severe ophthalmic complications, such as visual impairment or blindness. This disease is routinely treated with medical therapy and keratoplasty, and recently also with alternative regenerative therapies, like cross-linking, amniotic membrane transplant and laser. Plasma medicine is another recent example of regenerative treatment that showed promising results in reducing microbial load of corneal tissue together with maintaining its cells vitality. Since the effect of helium plasma application on corneal mechanical viscoelasticity has not yet been investigated, the aim of this study is first to evaluate it on ex vivo porcine corneas for different exposition times, and then to compare the results with previous data on cross-linking treatment. Results - 94 ex-vivo porcine corneas divided in 16 populations (healthy or injured, fresh or cultured corneas and treated or not with plasma or cross-linking), were analysed. For each population, a biomechanical analysis was performed by uniaxial stress-relaxation test and a statistical analysis was carried out considering the characteristic mechanical parameters. In terms of equilibrium normalized stress, no statistically significative difference resulted when the healthy corneas were compared to the lesioned plasma-treated ones, independently of the treatment time, contrary to what was obtained in relation to the cross-linking treated corneas exhibiting more intense relaxation phenomena. Conclusions - In this study, the influence of the Helium plasma treatment on the viscoelasticity of ex vivo porcine corneas was observed, by restoring in lesioned tissue a degree of relaxation similar to the one of native tissue, even after only 2 minutes of application. Therefore, the obtained results suggest the plasma treatment as a promising new regenerative ophthalmic therapy for melting corneal ulcers, laying the groundwork for further studies to correlate the mechanical findings to corneal histology and ultrastructural anatomy after plasma treatment.