The relationship between corneal thickness and pressure in rabbits eyes after LASIK surgery

• Aim: To study biomechanical changes in the cornea of rabbits in ex vivo after laser in situ keratomileusis(LASIK) surgery. To explore the relations between corneal biomechanical properties of rabbits and the central corneal thickness(CCT) and the intraocular pressure(IOP). • Methods: 1) A total of thirty eyes of fifteen New Zealand rabbits were included in the study. The thirty eyes were divided into three groups. Each group had ten eyes of five rabbits; ten eyes were incised 1/ 3 primary corneal thickness with excimer laser and ten eyes were incised 1/2; the other ten eyes were regarded as control. 2) The isolated cornea was cut into a round sample whose diameter is 15mm. The sample was put on the clamping apparatus, pressurized by cross-connection device and scanned with three dimensional laser scanner. At last changes of corneal anterior process of the corneal sample were analyzed under different pressures and different corneal thickness. 3) All the parameters were converted into logarithm and the measurement data were evaluated through variance analysis and tendency test. • Results: 1) The differences of corneal protrusion d_x (x = 10-80) (logd1) under different pressures are statistically meaningless in the three groups. 2) The differences of corneal protrusion d_x-₁₀ (x = 20-80) (log d2) between every experimental pressure and primary pressure among three groups are as below: 1) The differences between ablation 1/2 group and normal group, ablation 1/3 group are statistically meaningful (P <0.05). 2) The difference between normal group and ablation 1/3 group is statistically meaningless(P < 0.05). 3 The differences of corneal protrusion d_(x+10)-x (x = 10-70) (log d3) under adjacent pressures are statistically meaningless in the three groups. 4) Corneal protrusion under different pressures grows with the increase of pressure d_x(x = 10-80) (logd1), which has a linear trend. But the trend differences among the three roups are statistically meaningless. • Conclusion: 1) The change of corneal biomechanics has some relationship with CCT after LASIK surgery. The corneal biomechanics of ablation 1/3 group is close to that of normal group and in safety margin. The corneal biomechanics of ablation 1/2 group is obviously degraded. 2) There is certain relationship between IOP and the corneal biomechanics. When the IOP is high enough, the corneal anterior process is irreversible. 3) To insure the stability and security of LASIK, the residual corneal stroma-bed thickness must not be less than half of the primary thickness and IOP must be maintained at the low level of normal range.