Real-world comparison between the Tonopen and Goldmann applanation tonometry in a university glaucoma clinic

Purpose: To determine whether Tonopen intraocular pressure (IOP) measurements by Ophthalmic technicians are interchangeable with Goldmann applanation tonometry (GAT) by a specialist in our glaucoma clinic. Methods: Ophthalmic technician Tonopen and glaucoma specialist GAT IOP measurements were performed on both undilated eyes of 300 consecutive patients during the same visit to our glaucoma clinic. Results: Among all 600 eyes of 300 patients (age 65.4, range: 23–92 years, male: 44.3%), Tonopen and GAT IOPs were similar (15.5 ± 0.6 vs. 15.4 ± 0.7 mmHg, respectively, p = 0.63) and directly correlated (r² = 0.58, p < 0.0001). However, among 120 patients with bilateral primary open-angle glaucoma GAT IOP was significantly higher than Tonopen in the right eyes (17.1 ± 1.1 vs. 16.2 ± 0.9 mmHg, p = 0.024) and in the left eyes (17.0 ± 1.0 vs. 16.3 ± 1.0 mmHg, p = 0.029). In all 300 right eyes, Tonopen underestimated IOP in 48.3% of eyes and overestimated in 39% (difference range: (−)14 to (+)12 mmHg), with IOP difference > ± 3 mmHg in 34% of eyes. In eyes with GAT IOP ≥ 22 mmHg, Tonopen IOP was significantly lower (24.7 ± 2.6, range: 11–43 mmHg vs. 28.2 ± 2.2, range: 22–43 mmHg, p = 0.0002, mean difference: − 3.6 ± 1.7 mmHg), and the Tonopen measured IOP ≤ 21 mmHg in 33.3% of eyes. In eyes with Tonopen IOP ≤ 10 mmHg GAT measured IOP of 11–17 mmHg in 65.7% of eyes. Conclusions: Tonopen may mask a third of eyes with elevated IOP and two third of eyes with potentially above-goal IOP. The Tonopen may not be interchangeable with GAT or sufficiently reliable for patient management or screening in our glaucoma clinic. However, further study is recommended to assess the limitations of the Tonopen IOP measurements in eyes with higher or lower GAT IOPs. Clinical Trials Registration: The Institutional review board, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY does not require this retrospective study to register.