Corneal hysteresis with intraocular pressure of a wide range: A test on porcine eyes

PURPOSE: To investigate the relationship between corneal hysteresis (CH) and intraocular pressure (IOP) using porcine eyes in the low to high IOP ranges. METHODS: In vitro porcine eyes were used to investigate the relationship of CH and IOP. IOP was altered by changing the height of a drip stand within the dynamic range of 60 mm Hg. CH and IOP were measured with the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Depew, NY) at different heights. Sec-ond- order polynomial regression method was employed to assess the nonlinear correlation of CH and IOP. RESULTS: CH demonstrated an initial plateau stage with low IOP, which then decreased as IOP increased to higher values up to 60 mm Hg. The maximum CH value of approximately 6 to 8 mm Hg was achieved when IOP ranged from 11 to 25 mm Hg. The nonlinear regression lines of Goldmann correlated IOP (IOPg) and CH can be described as CH = -0.0029 x IOPg² + 0.1005 x IOPg + 5.2824, R² = 0.3676, P < .05. CONCLUSIONS: CH was relatively constant for lower values of IOP and showed a decreasing relationship at higher values of IOP. This nonlinear relationship provides insight into understanding the viscoelastic nature of CH over a wider range of IOP values. The experimental data on porcine eyes may indicate that IOP should be taken into account when analyzing the deformation response of the cornea to an applied air puff.