Clinical comparison of the Keeler Pulsair 2000, American Optical MkII and Goldmann applanation tonometers

The aim of our study was to evaluate the performance of both the Keeler Pulsair 2000 and the American Optical (AO) MkII non-contact tonometers (NCT) and compare these to the reference Goldmann standard using the same group of patients. Forty-five patients (89 eyes) receiving medical treatment for primary open angle glaucoma had their intraocular pressure (IOP) measured with each instrument in a random order using five experienced observers. In the IOP range of the sample (6-27 mmHg) the difference between means for each tonometer was small. The Pulsair 2000 (mean = 19.06 mmHg, SD 6.28) read slightly higher than Goldmann (mean = 18.01 mmHg, SD 4.88), whereas the AO MkII read slightly lower (mean = 16.27 mmHg, SD 5.93). However, all differences were statistically significant (P < 0.001, repeat measures ANOVA). Correlation coefficients for Pulsair 2000 versus Goldmann was r = 0.82 and for AO MkII versus Goldmann was r = 0.85. In addition, the repeatability for each NCT was assessed using 10 consecutive measurements on a further 10 subjects. The Pulsair 2000 showed significantly greater variation of IOP (mean SD 3.43 mmHg) than the AO MkII (mean SD 1.76 mmHg), confirming the need for taking at least four readings per eye with the Pulsair 2000. These variations are greater than that generally observed with Goldmann, and possible explanations why this occurs are discussed. In conclusion, subject to these limitations, both NCTs should be useful for measuring IOP as part of a screening protocol for glaucoma.