The Difference in Intraocular Pressure Readings Between 3 Applanation Tonometers is Independent of Central Corneal Thickness, in Glaucomatous and Nonglaucomatous Eyes

Abstract

To look at tonometry differences between 3 tonometers and to correlate this difference with central corneal thickness (CCT) in glaucomatous and nonglaucomatous eyes. A total of 145 patients were recruited (39 with glaucoma). Intraocular pressure (IOP) was carried out using the Tonosafe (TS), Tono-Pen XL (TP), and Goldmann applanation tonometer (GAT). CCT was also performed using a digital pachymeter. The TS underestimated IOP when compared with the GAT by a mean (±SD) of 1.03±2.14 mm Hg (P<0.001). The TP when compared to the GAT overestimated IOP by a mean (±SD) of +1.09±6.38 mm Hg (P=0.071). We found only 31% of TP readings to be within ±2 mm Hg of the GAT readings and only 60% to be within ±4 mm Hg of the GAT readings. Correlation was poor (F=0.247) between the GAT and TP with the coefficient of determination being 0.061. The difference in IOP was independent of CCT and a diagnosis of glaucoma. The TS, when compared with the GAT, underestimates IOP with a tendency for this to increase in the higher range of IOP readings. The TP is poorly correlated with the GAT.