We enjoyed reading the article by Li et al.1 We would be most grateful if the authors could elaborate on the following issues.
First, in their study, the intraocular pressures (IOPs) were measured by Goldmann, TonoPen (Mentor, Norwell, Mass), and Proview (Bausch & Lomb, Rochester, NY) tonometers, in that order for all subjects. It is known that repeated tonometry will produce a massaging effect on the eyeball that will lower the IOP.2 Incidentally, the mean IOPs measured by the 3 instruments were in the same descending order: eg, in the right eye, the mean IOPs were 17.2 mm Hg, 15.6 mm Hg, and 13.8 mm Hg by Goldmann, TonoPen, and Proview tonometers, respectively. It is therefore uncertain whether the differences in results were partially accounted for by the massaging effect. The authors thought that it was a remote possibility that the order of IOP measurement contributed significantly to the difference because at least 2 minutes were allowed to elapse between measurement methods. In the article that they cited to support their argument,3 its conclusion reads, “We recorded a statistically significant difference between the first and the second IOP measurements at 1-, 3-, 4-, and 5-minute intervals. The differences were not significant at 2- and 10-minute groups.”3 Thus, if we accept the recommendation from this study, it is not entirely true that a time lapse of at least 2 minutes would be acceptable. It appears to be more desirable to employ the 3 instruments in random order, which is regarded as a valid methodology to even out the effect of massaging.
Leung DYL, Lam DSC. Clinical Comparison of the Proview Eye Pressure Monitor With the Goldmann Applanation Tonometer and the TonoPen. Arch Ophthalmol. 2005;123(4):578-579. doi:10.1001/archopht.123.4.578-c