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P. M. Drayna, M. C. Neuffer, V. Panday, C. Reilly; Comparison of Intraocular Pressures after Photorefractive Keratectomy Using the Perkins Tonometer, Dynamic Contour Tonometer, Pneumatonometer and the Tono-Pen. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1481.
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The Goldmann applanation tonometer(GAT) is the gold standard for measuring intraocular pressure(IOP) in patients. However, GAT has been demonstrated to be inaccurate in patients after photorefractive keratectomy(PRK). The Dynamic Contour Tonometer(DCT) is a new tonometer with an electronic pressure sensor reported to be independent of corneal thickness. This study is a prospective animal study comparing the accuracy of the DCT to the Perkins tonometer, pneumatonometer, and the Tono-Pen in measuring IOP in sixteen post-PRK New Zealand White rabbits.
Sixteen rabbits received a standard 6.0mm diameter, 100µm depth PRK ablation in the right eye, with the left eye as the control. Approximately 4 weeks later, after sufficient healing of the epithelium, the rabbits were examined under anesthesia. Both eyes were cannulated and IOPs of 10, 20, 30, and 40 mmHg were created by a syringe filled with BSS and confirmed by a pressure transducer placed in the anterior chamber. At each IOP level, the Perkins, DCT, pneumatonometer, and Tono-Pen were used to measure IOPs. Data were analyzed using a repeated measures analysis of variance (RM ANOVA) of the mean absolute difference between the tonometers and corresponding pressure transducer measurement.
We found no statistically significant difference (p<.05) between the DCT, Tono-pen, or pneumatonometer at the 10, 20, 30 or 40 mmHg IOP levels in the treated or control eyes. There was a statistically significant difference between the Perkins and each of the other three tonometers at 10 mmHg in the treated eyes. All of the tonometers showed a significant (p<.05) increase in deviation from the pressure transducer with higher IOP (30-40mmHg) in both treated and control eyes.
The DCT demonstrates similar accuracy in measuring IOP in post PRK eyes as the pneumatonometer and Tono-Pen. The Perkins tonometer shows less accuracy than the other three in post PRK measurements. All four of the tonometers demonstrate less accuracy with higher intraocular pressures.
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