Measurement of Intraocular Pressure in a Porcine Ex Vivo Model Eye

Aims: To compare the pressure inside and outside the pig eye in relation to the location of cannulation for the injection of liquid into the anterior or vitreous chamber.

Method: Eleven enucleated pig eyes were used. 46 measurements of intraocular pressure IOP were taken with a Perkins tonometer when the eye was cannulated in the anterior chamber. 49 measurements were taken when the eye was cannulated in the vitreous chamber. The eyeball was connected to a low-pressure transducer to control, maintain and modify the pressure in the eyeball.

Results: No significant difference (P=0.138) was found between the Perkins pressure measurements from cannulations in the anterior and vitreous chambers. A linear relationship between transducer and Perkins measurements was found when the eye was cannulated in the anterior chamber (IOP=-7.749+0.763 transducer; R2=0.940, p<0.001) and when it was cannulated in the vitreous chamber (IOP=-7.476+0.730 transducer, R2=0.885, p<0.001). No difference was found between the Perkins/transducer pressure ratios (P=0.500 ANOVA) from cannulations in anterior and vitreous chambers. There were no differences in the measurements among eyes that could affect pressure outcomes. A direct relationship between the insufflate pressure inside the eyeball and the Perkins pressure was found.

Conclusion: The pressure measured by Perkins applanation tonometry in an ex vivo porcine eye model is not correlated with the area of cannulation, keeping constant pressure with a low-pressure transducer. A linear equation was generated that correlates the pressure gauge with IOP Perkins, which would apply to future studies that use the pig eye as an exvivo animal model of hypertension in glaucoma.