Comparative Evaluation of Classic Mechanical and Digital Goldmann Applanation Tonometers

Abstract

Objectives: The objective of this study was to evaluate the agreement and clinical interchangeability of intraocular pressure (IOP) measurements obtained with the mechanical Haag-Streit AT900 Goldmann applanation tonometer (mGAT) and the digital Huvitz HT5000 applanation tonometer (dGAT). Methods: This retrospective comparative study included 53 eyes of 28 patients undergoing routine ophthalmologic evaluation. Each eye underwent IOP measurement using both mGAT and dGAT in a randomized sequence. Central corneal thickness (CCT) was also recorded. Pearson's correlation coefficient was used to determine correlation between paired IOP measurements. Bland-Altman plots were graphed for the analysis of differences for IOP between the instruments. Results: A total of 53 eyes of 28 patients (15 males) were included in the study. The mean age of the patients was 62.6 years. The mean mGAT and dGAT measurements were 16.3 ± 6.6 mmHg (range 9-50) and 16.4 ± 6.2 mmHg (range 8.8-45.9), respectively (p = 0.53). A strong, significant positive correlation was found for paired IOP measurements by the two instruments (r = 0.98; p < 0.0001). Bland-Altman analysis revealed 95% limits of agreement from -2.5 to +2.3 mmHg, with a small but statistically significant proportional bias favoring mGAT at higher IOP levels. Additionally, 91% of paired measurements were within ±2 mmHg. CCT-related differences were statistically and clinically insignificant. Conclusions: IOP measurements obtained with mGAT and dGAT were highly correlated and clinically interchangeable for the range tested. The Huvitz HT5000 may serve as a reliable alternative to the classic Goldmann tonometer in routine clinical settings.

Keywords: Goldmann tonometer; applanation tonometry; device comparison; digital tonometry; intraocular pressure.

Figure 1

Correlation between IOP measurements (mmHg) obtained using mGAT and dGAT. A strong, statistically significant linear correlation was observed (r = 0.98, p < 0.0001). (IOP: Intra ocular pressure; mGAT: Haag-Streit AT900 mechanical Goldmann tonometer; dGAT: Huvitz HT5000 digital Goldmann tonometer).

Figure 2

Bland–Altman analysis comparing IOP measurements from mGAT and dGAT (mmHg). The mean difference (bias) is centered near zero, with 95% limits of agreement from −2.5 mmHg to +2.3 mmHg. A weak but statistically significant proportional bias was detected (r = 0.35, p = 0.011), suggesting a tendency for mGAT to yield higher readings at higher IOP levels. (IOP: Intra ocular pressure; mGAT: Haag-Streit AT900 mechanical Goldmann tonometer; dGAT: Huvitz HT5000 digital Goldmann tonometer).

Figure 3

Relationship between CCT (µm) and the difference in IOP measurements (mGAT − dGAT, mmHg). A weak, non-significant positive correlation was observed (r = 0.13, p = 0.61), with minimal influence of CCT on inter-device variability. Regression equation: Difference = (0.0021 × CCT) − 1.505. (IOP: Intra ocular pressure; mGAT: Haag-Streit AT900 mechanical Goldmann tonometer; dGAT: Huvitz HT5000 digital Goldmann tonometer; CCT: Central corneal thickness).