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Rabbits are commonly used as animal models for the evaluation of drugs and surgery to lower intraocular pressure (IOP).The accuracy of IOP measurement is therefore critical in the analysis of data and subsequent extrapolation to humans.An accurate method to measure rabbit IOP is intracameral manometry,but it is an invasive way.Schiötz,Perkins and Rebound were often used in clinic.However,their accuracy in measuring rabbit IOP in experimental study is unclear.
The purpose of this study was to investigate the accuracy of IOP measured by Schiötz tonometer,Perkins tonometer and Rebound tonometer relative to intracameral manometry in New Zealand white rabbits.
The central corneal thickness (CCT),corneal curvature (CC),axial length (AL),anterior chamber depth (ACD), lens thickness (LT) and scleral thickness (ST) were respectively measured in 8 eyes of 8 healthy New Zealand white rabbits with lenstar900 and ultrasound biomicroscopy (UBM).The actual IOP was measured with a 24G needle inserted the anterior chamber and connected to a pressure transducer under the general anesthesia,the IOP gradient was set with a 24G needle inserting the vitreous cavity and connecting to a container with balanced salt solution(BSS).Then,comparative measurements at the same pressures were performed with three types of tonometers.The IOP values from Schiötz tonometer,Perkins tonometer and Rebound tonometer were calibrated based on actual IOP from intracameral manometry and eyeball physiological parameters by multiple regression equation.
The mean of CCT,CC,AL,ACD,LT and ST was (338.96±21.52) μm,(51.68±1.66) D,(14.63±0.19) mm,(2.22±0.04) mm,(6.15±0.10) mm and (339.80±47.41) μm.Compared with the intracameral manometry value (IMV),the error range was (17.08±11.22) mmHg in the Schiötz tonometer value (STV),(25.81±12.43) mmHg in the Perkins tonometer value (PTV) and (22.50±11.47) mmHg in the Rebound tonometer value (RTV),with significant differences between them(t=10.54,14.39,13.59,all at P<0.05).Compared with IMV,the 95% limits of agreement of three portable tonometer values is larger,and three portable tonometer values had the greater measurement error with elevated IOP gradient.The regression equations was IOP=141.015+1.570×STV+0.122×CCT-3.480×CC between actual IOP and STV (R=0.92,P=0.00),IOP=-33.323+1.914×PTV+0.133×CCT between actual IOP and PTV(R=0.88,P=0.00),IOP=160.395+1.866×RTV+0.201×CCT+34.554×LT-2.649×CC+0.063×ST between actual IOP and RTV (R=0.95,P=0.00).
The physiological parameters of rabbit eyeball are obviously different from human. The STV, PTV and RTV have a great measuring error in comparson with actual IOP, and therefore it is necessary to correct STV, PTV and RTV based on the ocular physiology parameters in experimental study.