Indian Journal of Ophthalmology (Jan 2000)
Tonometry in normal and scarred corneas, and in postkeratoplasty eyes : A comparative study of the Goldmann, the ProTon and the Schiotz tonometers.
Abstract
PURPOSE: Clinical comparison of intraocular pressure (IOP) measured with the Goldmann applanation tonometer (GAT), the ProTon tonometer (PT), and the Schiotz tonometer (ST), in normal eyes, eyes with scarred corneas and postkeratoplasty eyes. MATERIAL AND METHODS: The IOP readings with GAT, PT, and ST were compared in 125 eyes with normal corneas (Group A), 17 eyes with scarred corneas (Group B), and in 21 postkeratoplasty eyes (Group C). The data were statistically analysed at 95% confidence interval; linear regression analysis and paired t-test were done. RESULTS: The mean differences and their standard deviation [SD] between GAT and PT readings, and GAT and ST readings respectively were: [1] in Group A: -0.23 [SD 2.75] mmHg and +0.24 [SD 3.18] mmHg respectively; [2] in Group B: -1.8 [SD 12.67] mmHg and -4.5 [SD 9.95 mmHg; and [3] in Group C: +0.24 [SD 8.72] mmHg and -0.12 [SD 8.7] mmHg. They were not statistically significant. In Group A the 95% confidence interval between GAT and PT readings was -5.27 mmHg to 5.73 mmHg, and between GAT and ST readings, -6.12 mmHg to 6.59 mmHg. Ninety six [77%] eyes with the PT and 84 [69%] eyes with ST measurements were within 3 mmHg of GAT pressure. The correlation coefficients [r] for PT and ST were 0.93 [P = 0.0000] and 0.88 [P = 0.0000] respectively. In Group B 95% confidence interval between GAT and PT readings was -27.17 mmHg to 23.51 mmHg, and between GAT and ST measurement, -24.37 mmHg to 15.44 mmHg. The correlation coefficients [r] for the PT and ST were 0.112 [P = 0.660] and 0.630 [P = 0.006] respectively. In group C, the 95% confidence interval between GAT and PT measurements was -17.20 mmHg to 17.67 mmHg, and between GAT and ST measurements, -17.51 mmHg to 17.27 mmHg. The correlation coefficients [r] for the PT and the ST were 0.780 [P = 0.0000] and 0.740 [P = 0.0001] respectively. CONCLUSIONS: In clinical practice PT appears to have a higher level of accuracy than ST in normal corneas. In scarred corneas and post-penetrating keratoplasty eyes, because of high SD for mean differences and wide confidence interval of 95%, both PT and ST are inaccurate in measuring IOP as compared to GAT in such eyes.
