Comparison of the Intraocular Pressure Measurement between Rebound Tonometer and Tonopen in Rats

ABSTRACT

PURPOSE: To compare the rebound tonometer with the TonoPen for measuring the intraocular pressure (IOP) in rats METHODS: Chronic IOP elevation models were induced unilaterally in nine Sprague-Dawley rats by applying an argon laser to the trabecular meshwork. IOP was measured before laser treatment and at one, two, and three days following laser treatment. Two independent operators collected five readings of the rebound tonometer and the TonoPen. Correlation analysis and comparison with the Bland & Altman method were performed. The intraclass correlation coefficient of each measurement and the difference between two independent operators were calculated. RESULTS: The IOP values measured with the rebound tonometer were well correlated with those of the TonoPen (r=0.676, p<0.001); however, the mean difference expressed as the percent difference of the averages of two tonometers, was 27.5%. The IOP values measured with a rebound tonometer exhibited a significantly higher intraclass correlation coefficient (0.966; 95% CI, 0.945-0.980 vs 0.412; 95% CI, 0.264-0.581) and a lower difference between the two operators (3.10+/-2.17 mmHg vs 6.17+/-5.17 mmHg) than those of the TonoPen. CONCLUSIONS: Although the IOP values measured with the rebound tonometer were lower than those of the TonoPen, they were in good agreement and were less variable than those of the TonoPen.