Stress and continuous relaxation spectrum of porcine cornea after LASIK / 国际眼科杂志(Guoji Yanke Zazhi)

ABSTRACT

AIM: To explore the characteristic of relaxation of porcine cornea after LASIKMETHODS: Usual LASIK was performed on fresh porcine corneas with stable intraoculer pressure (IOP) maintained through optic nerve irrigation. The ablation depth on stroma is 30%, 50% and 70% respectively. Then the dumbbell-shaped corneal strip specimens were cut and stored in 20% Human Albumin solution for use (4℃).Sip up the Albumin solution on specimens, and fixed them on homemade jig. Stress relaxation tests were erformed on Tytron250 Dynamics Experiment System. the loading speed was 385mm/min,extending ratewas 1.5, and relaxation time was 1 000s. The data werecollected electronically and automatically.RESULTS: In LASIK procedure, though a single flap-cutting can cause a little reduction of corneal stress relaxation (P＜0.05,P=0.49), the cornea may still remain its property of visco-elasticity. When ablation depth was 30% or more, corneal stress relaxation decreased to almost one half (P＜0.01).The change of corneal stress relaxation degree in vertical meridian specimen was lower than that in horizontal specimen, especially when ablation depth was 70%, and it's statistically significant (P＜0.001). In LASIK operation, the more depth the ablation, the more reduce the stress relaxation degree, and it's easy to cause deformation and creep deformation.CONCLUSION: The changes of the stress relaxation in verticai and longitudinal meridian specimens are similar, and slightly obvious in longitudinal specimen, especially in 70%ablation group.