Goldmann tonometry versus the Tono-Pen XL for intraocular pressure measurement: an evaluation of the potential impact on clinical decision making in glaucoma

Aim:  To assess the validity of the Tono-Pen XL as an alternative to the Goldmann applanation tonometer (GAT) for the measurement of intraocular pressure (IOP) in patients with ocular hypertension (OHT) and glaucoma.
Methods:  Over a 3 month period, patients with OHT or glaucoma attending a general clinic had IOP measurements taken using the Tono-Pen XL and the GAT. Tono-Pen measurements were taken by suitably trained nursing staff, while Goldmann tonometry was performed by the examining ophthalmologist.
Results:  There were 124 eyes of 62 patients in this study. Overall, mean IOP was 18.3 ± 4.8 mmHg using GAT and 18.8 ± 5.5 mmHg using the Tono-Pen. Using the Bland–Altman method, the upper and lower limits of agreement between the two devices were +10.6mmHg and ?9.6 mmHg, respectively. Significant over- and under-estimates of IOP were noted in 10 (16%) patients.
Conclusion:  Our findings suggest that the Tono-Pen XL cannot be used as a substitute for GAT in the management of patients with glaucoma or OHT.