title: Comparison between Tonopachy and other tonometric and pachymetric devices.
abstract: OBJECTIVE
  This study aimed to compare central corneal thickness (CCT) measurement by Tonopachy to that by Pentacam and ultrasound pachymetry, and intraocular pressure (IOP) measurement to that by Goldmann applanation tonometry (GAT). The reproducibility of CCT and IOP measurements by Tonopachy was also evaluated.
  
  
  METHODS
  In 104 eyes of 104 patients, CCT was measured by Tonopachy, Pentacam, and ultrasound pachymetry, and IOP was measured by Tonopachy and GAT. Each CCT and IOP measurement was compared using Pearson correlation, repeated measures analysis of variance, and Bland-Altman plots. In 30 subjects, CCT and IOP measurements by Tonopachy were repeated to evaluate intrasession and intraobserver variability.
  
  
  RESULTS
  Both CCT and IOP measurements were highly correlated among all instruments used in this study. CCT measurements by three pachymeters were statistically different (p<0.0001). CCT measured by ultrasound pachymetry was lowest (541.7 ± 30.6 μm) whereas those by Tonopachy and Pentacam showed no difference (557.3 ± 34.3 and 558.0 ± 33.7 μm, respectively). Tonopachy overestimated CCT by 13.9 μm when compared with ultrasound pachymetry. There was a statistically significant difference between IOP measurements by two tonometers (p<0.0001); IOP measurement was higher by Tonopachy than by GAT (13.9 ± 4.2 and 12.5 ± 3.2 mm Hg, respectively). Tonopachy overestimated IOP measurements by 1.2 mm Hg compared with GAT. Intersession agreements for IOP and CCT measurements by Tonopachy were excellent (intraclass correlation, 0.902 and 0.962, respectively) with 95% limits of agreement ranging from -1.4 to 2.2 mm Hg and from -12.9 to 12.1 μm, respectively.
  
  
  CONCLUSIONS
  Although CCT and IOP measurements obtained by Tonopachy were reproducible and showed close agreement with ultrasound pachymetry and Pentacam, and GAT, careful attention should be paid when comparing Tonopachy CCT measurement to ultrasound pachymetry or its IOP measurement to GAT as the values may not be interchangeable. Tonopachy is a reliable instrument for evaluating CCT and IOP.
authors.affiliation: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Yong Gi
authors.initials: YG
authors.lastname: Lee
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Kim
authors.forename: Na Rae
authors.initials: NR
authors.lastname: Kim
authors.forename: Chan Yun
authors.initials: CY
authors.lastname: Kim
authors.forename: Eun Suk
authors.initials: ES
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation* / Q000592:standards; D014463:Ultrasonography; D055815:Young Adult