title: Correspondence of Tono-Pen intraocular pressure measurements performed at the central cornea and mid-peripheral cornea.
abstract: BACKGROUND
  As the awareness of the influence of central corneal thickness (CCT) on Goldmann tonometry has increased, many publications have questioned the accuracy of Goldmann intraocular pressure (IOP) measurement. The Tono-Pen, because it indents a much smaller surface area when compared to a Goldmann probe, may be less affected by corneal thickness variations when compared with Goldmann tonometry.
  
  
  METHODS
  Forty human subjects with no history of refractive surgery participated in this study. The IOP of the right eye of each subject was measured with the Goldmann tonometer, the Tono-Pen at the central cornea, and the Tono-Pen at the mid-peripheral cornea. An ultrasonic DGH Pachette pachymeter was used to measure the central and mid-peripheral corneal thickness at the location of the IOP readings.
  
  
  RESULTS
  Tono-Pen measurements at the central and mid-peripheral cornea highly correlated (r = 0.933), and did not significantly differ (p = 0.646). The IOP readings with the Goldmann tonometer (r= 0.406), the Tono-Pen at the central cornea (r = 0.453), and the Tono-Pen at the mid-peripheral cornea (r = 0.321) showed a positive correlation to corneal thickness. The Goldmann and Tono-Pen tonometers differed significantly in the measurement of IOP at the central cornea (p = 0.007), but were positively correlated (r = 0.674).
  
  
  CONCLUSIONS
  The Tono-Pen IOP measurement at the central cornea highly approximated Tono-Pen IOP measurement at the mid-peripheral cornea. Furthermore, although not highly correlated, both the Goldmann and Tono-Pen tonometers showed a significantly positive correlation between IOP and corneal thickness measurements.
authors.affiliation: Albuquerque VA Medical Center, Eye Clinic, Albuquerque, New Mexico 87108, USA. Michael.Sullivan-Mee@med.va.gov
authors.forename: Michael
authors.initials: M
authors.lastname: Sullivan-Mee
authors.forename: Fortsmith
authors.initials: F
authors.lastname: Pham
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D003315:Cornea / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008365:Manometry / Q000295:instrumentation*; D008875:Middle Aged; D012016:Reference Values; D014463:Ultrasonography