Comparison of the Tono-Pen to the Goldmann applanation tonometer

Oculab Tono-Pen tonometry was compared with Goldmann applanation tonometry in 142 eyes of 71 patients without corneal problems. Overall we found 63% of the Tono-Pen readings to be within +/- 2 mm Hg of the Goldmann applanation tonometry readings and 77% to be within +/- 3 mm Hg, while 4% were within at least +/- 7 mm Hg difference. The correlation coefficient between the readings of the two instruments was .84. The mean value of the paired differences was 0.81 +/- 3.09 mm Hg overall, -1.78 +/- 1.86 mm Hg in the 4 to 10 mm Hg interval, 0.07 +/- 2.97 mm Hg in the 11 to 20 mm Hg interval, 1.27 +/- 2.62 mm Hg in the 21 to 30 mm Hg interval, and 4.15 +/- 2.28 mm Hg in the 31 to 45 mm Hg interval. We conclude that the Tono-Pen measures intraocular pressure in a manner that corresponds well to the Goldmann tonometer in the 11 to 20 mm Hg interval, and fairly well in the 4 to 10 mm Hg and 21 to 30 mm Hg intervals. It lacks good correspondence in the 31 to 45 mm Hg interval.