Is viscoelastic the corneal tissue? [Il tessuto corneale è viscoelastico?]

Purpose: To compare the known viscoelastic properties of soft tissues with singular published observations on the behaviour of corneal tissue. Materials and methods: The behaviour of the maxwellian element, typical viscoelastic biomechanical model, is compared with that of various previously studied soft tissues of animals. The same comparison can be made between stress-strain curves of riboflavin and UVA treated and untreated strips of human and porcine corneal tissue, stretched at constant velocity, from the literature. Results: The asymptotic stress-strain curves of the various soft tissues previously examined could be faithfully simulated by the Maxwell viscoelastic element. The exponential stress-strain curves of samples of corneal tissue were clearly different. Conclusions: The observed divergence demonstrates incompatibility between the alleged behaviour of corneal tissue and the viscoelastic properties attributed to it. Thus there are two possibilities: either corneal tissue is viscoelastic and the experiment showing exponential behaviour suffers from some technical problem, or the data is correct and corneal tissue is not viscoelastic. In either case further research is necessary for correct interpretation of the mechanism of cross-linking and for consequent therapeutic choices.