Comparison of Intraocular Pressure Measurements with Different Contact Tonometers in Young Healthy Persons

AIM: To analyze the correlation of Goldmann applanation tonometer (GAT), I-Care tonometer and Tono-Pen tonometer results in young healthy persons, and to investigate the influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurements recorded with these tonometers.METHODS: We conducted a pilot clinical study in 78 eyes of 78 subjects aged 22-28 years old (44 women and 34 men; mean age 23.8 +/- 1.19y). IOP was measured using GAT, I-Care and Tono-Pen tonometers, followed by measurements of CCT. Statistical analysis was performed using SPSS 20.0.RESULTS: The mean IOPs and standard deviation (+/- SD) for GAT, I-Care and Tono-Pen were 15.62 +/- 2.281 mm Hg, 1629 +/- 2.726 mm Hg and 16.32 +/- 2393 mm Hg, respectively. The mean CCT was 555.15 +/- 29.648 mu m. Clear positive correlations between GAT and I-Care, GAT and Tono-Pen, and I-Care and Tono-Pen tonometers were found (r=0.867, P<0.001; r=0.861, P<0.001; r=0.915, P<0.001, respectively). In comparison between devices, Bland Altman analysis showed a significant mean difference (MD) in the measurements by GAT and I-Care of -0.679 mm Hg and by GAT and Tono-Pen of -0.705 mm Hg( P<0.001), but there was no significant difference between I-Care and Tono-Pe(P >0.05). Both non-gold standard tonometers were affected by CCT; that is, both I-Care and Tono-Pen tonometer values were significantly higher with higher CCT means (>555 mu m; MD=-1.282, P<0.001; MD=-0.949, P<0.001, respectively) compared with GAT.CONCLUSION: Both I-Care and Tono-Pen tonometers overestimated IOP compared with the GAT values. Either the I-Care or Tono-Pen tonometer could be used instead of GAT because there was no significant difference between their results. Higher CCT values (>555 mu m) were associated with overestimated IOP values.