The Research Of The Corneal Biomechanical Properties

Objective: In ex vivo to research biomechanical changes in the cornea of rabbits after excimer laser incision as would be performed in laser in situ keratomileusis. To develop a relation among the corneal biomechanical property of rabbits and the central corneal thickness and the intraocular pressure. To expect this relationship can supply reference for the patients who would be performed in laser in situ keratomileusis during preoperative screening and postoperative treatment.Method: 1. A total of thirty eyes of fifteen New Zealand rabbits were internalize in the study. The thirty eyes were divided into three groups. Each group had ten eyes of five rabbit; ten eyes were incise 1/3 primal corneal thickness with excimer laser and ten eyes were incise 1/2, the other ten were control. 2. Two rabbits were killed at once after surgery every time. The isolated cornea was cut into a round sample which diameter is 15mm. The sample was put on the clamping apparatus. To pressurize by cross-connection device and scan with three dimensional laser scanning. At last to analyze changes of corneal forward shift of the corneal sample under different pressures and different corneal thickness. To analyze the relationship of corneal thickness and IOP with the change of corneal forward shift. 3. All the parameters were convert into logarithm, then the measurement data were evaluate using variance analysis and tendency testResult: 1. The differences of corneal protrution under different pressures grows with the growing of pressure d_x (x=10～80) (logd1) are statistically meaningless in the three groups. 2. The differences of corneal protrution d_x-10 (x=20～80) (logd2) under three groups of every experimental pressure and primary pressures are as below: The differences of ablation1/2 group with normal group and ablation1/3 group are statistically meaningful. The differences of normal group with ablation 1/3 group are statistically meaningless. 3. The differences of corneal protru-tion d_(x+10)-x(x=10～70) (logd3) under adjacent pressures are statistically meaningless in the three groups. 4. corneal protrution under different pressures grows with the growing of pressure d_x (x=10～80) (logd1),It has a linear trend.but the trend differences among the three groups are statistically meaningless. Conclusion: 1. The change of corneal biomechanics has some relationship with thickness and pressure.The corneal biomechanics of ablationl/3 group is closed to nomal and in safety margin. The corneal biomechanics of ablationl/2 group is obviously degrade. 2. There is the relationship between IOP and The corneal biomechanics. When the IOP is enough high ,the corneal forward shift is irreversible. 3. As to insure the stability and security of lasik, the residual corneal stroma-bed thickness must be less than half of the primary thickness and IOP must maintain at the low level of normal pressure.