Aims/objectives: Tonometry is a fundamental procedure in the diagnosis and management of glaucoma. Different tonometers have been proposed but none are as accurate as the Goldman applanation tonometry (GAT). Nonetheless, due to the limitations of GAT, mobile tonometry methods became prevalent. This study aims to examine the reliability of the Tono-Pen AVIA® (TPA) in measuring intraocular pressure (IOP) across different postures.
Methods: A total of 196 eyes were prospectively examined for IOP changes using GAT and TPA. IOP measurements were taken across different postures using the TPA. Reliability of measurements was compared using interclass correlation coefficients (ICC), while agreement was represented using Bland-Altman analysis. Pearson r coefficient was used to measure correlations.
Results: When compared to GAT (14.5 ± 4.4 mmHg), IOP readings were significantly higher for TPA at both seated (16.5 ± 4.5 mmHg; p < 0.001) and supine (16.9 ± 5.7; p < 0.001) positions. The ICC values for GAT and TPA among seated and supine patients were 0.79 (0.54-0.90) and 0.76 (0.48-0.87) indicating good reliability between the readings. There were significantly positive correlations between GAT and TPA at both seated (r = 0.626, p < 0.001) and supine (r = 0.727, p < 0.001) positions. Per Bland-Altman analysis, limits of agreement were -8.57 to 4.37 for GAT and seated TPA and -10.34 and 5.34 for GAT and supine TPA.
Conclusion: Good reliability exists between IOP measurements using GAT and TPA. However, the devices are not interchangeable and therefore cannot be used reciprocally in the same patient.
Keywords: Tonometer; intraocular pressure; posture; tonopen; validation.