title: Comparison of intraocular pressure measurements with different contact tonometers in young healthy persons.
abstract: OBJECTIVE
  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, 16.29±2.726 mm Hg and 16.32±2.393 mm Hg, respectively. The mean CCT was 555.15±29.648 µm. 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-Pen ( 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 µm; MD=-1.282, P<0.001; MD=-0.949, P<0.001, respectively) compared with GAT.
  
  
  CONCLUSIONS
  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 µm) were associated with overestimated IOP values.
authors.affiliation: Center of Eye Diseases, Vilnius University, Vilnius LT-08661, Lithuania.
authors.forename: Saulius
authors.initials: S
authors.lastname: Galgauskas
authors.affiliation: Center of Eye Diseases, Vilnius University, Vilnius LT-08661, Lithuania.
authors.forename: Rasa
authors.initials: R
authors.lastname: Strupaite
authors.affiliation: Center of Eye Diseases, Vilnius University, Vilnius LT-08661, Lithuania.
authors.forename: Ernesta
authors.initials: E
authors.lastname: Strelkauskaite
authors.affiliation: Center of Eye Diseases, Vilnius University, Vilnius LT-08661, Lithuania.
authors.forename: Rimvydas
authors.initials: R
authors.lastname: Asoklis
keywords: Goldmann tonometer; I-Care tonometer; Tono-Pen tonometer; corneal thickness; intraocular pressure