Tono-Pen Versus Goldmann Applanation Tonometry: A Comparison of 898 Eyes

Purpose: To compare the agreement in intraocular pressure (IOP) measurements obtained with the Tono-Pen (Reichert, Inc, Depew, NY) and Goldmann applanation tonometry (GAT). The influence of central corneal thickness (CCT) on IOP agreement between the 2 tonometry methods also was evaluated.

Design: Database study.

Participants: A total of 898 patients from the Research, Innovation and Experimentation Database spanning 1999 through 2016.

Methods: A total of 898 IOP measurements of right eye obtained with GAT and the Tono-Pen were extracted from a glaucoma, glaucoma suspect, and ocular hypertension clinical database. The agreement between IOP measurements obtained by the 2 methods was analyzed using a Bland-Altman plot in Microsoft Excel (Microsoft, Redmond, WA). Their relationship to CCT was evaluated using linear regression analysis.

Main Outcome Measures: Agreement between GAT and Tono-Pen measurements of IOP and influence of CCT on tonometry methods.

Results: The correlation between both tonometry devices was 0.76 (P < 0.001). The mean difference (Tono-Pen minus GAT) in IOP measurement was -0.15 mmHg (95% confidence limits, ±6.8 mmHg). The Tono-Pen underestimated GAT measurements at IOP of more than 16.8 mmHg and overestimated at IOP of less than 16.8 mmHg. Larger differences were associated with higher IOPs. An average difference of more than 3 mmHg by the Tono-Pen was observed for IOPs of 29 mmHg or more. A thicker cornea also was associated with higher IOP. A change of 0.16 mmHg for a 10-μm increase in CCT was appreciated for GAT, and one of 0.15 mmHg per 10 μm was appreciated for the Tono-Pen (all P < 0.001).

Conclusions: In a large cohort of more than 898 measurements, the average difference between IOP measured by GAT and the Tono-Pen was less than 1 mmHg, although the limits of agreement were wide. Higher IOPs were associated with larger differences.