title: Effect of central corneal thickness, corneal curvature, and axial length on applanation tonometry.
abstract: OBJECTIVE
  To evaluate the effect of central corneal thickness (CCT), corneal curvature, and axial length on applanation tonometry in an in vivo study.
  
  
  METHODS
  In a masked, prospective clinical trial, we examined 125 eyes of 125 patients scheduled for cataract surgery. Corneal curvature was measured by means of keratometry and axial length by A-scan ultrasonography. By cannulating the anterior chamber before surgery, intraocular pressure (IOP) was set to 20, 35, and 50 mm Hg in a closed system by means of a water column. After measuring thickness, the IOP was measured with an applanation tonometer. Pearson product moment correlations and multiple linear regression analyses were performed, and significance levels were evaluated by the paired, 2-tailed t test.
  
  
  RESULTS
  The difference between measured and real IOP was significantly dependent (P < .001) on CCT. The associations between IOP and corneal curvature or IOP and axial length were not statistically significant (P = .31). The association between IOP reading and CCT is shown in the "Dresdner correction table," which illustrates an approximately 1-mm Hg correction for every 25-microm deviation from a CCT of 550 microm. The correction values were positive as thickness decreased and negative as thickness increased.
  
  
  CONCLUSIONS
  Central corneal thickness significantly affects IOP readings obtained by applanation tonometry according to the Goldmann principle. A correction of IOP readings by considering CCT according to the Dresdner correction table might be helpful for determining an accurate IOP value.
authors.affiliation: Department of Ophthalmology, University Carl Gustav Carus, Dresden, Germany. Markus.Kohlhaas@jojo-dortmund.de
authors.forename: Markus
authors.initials: M
authors.lastname: Kohlhaas
authors.forename: Andreas G
authors.initials: AG
authors.lastname: Boehm
authors.forename: Eberhard
authors.initials: E
authors.lastname: Spoerl
authors.forename: Antje
authors.initials: A
authors.lastname: Pürsten
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Grein
authors.forename: Lutz E
authors.initials: LE
authors.lastname: Pillunat
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001837:Body Weights and Measures; D003315:Cornea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D005123:Eye / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D014065:Tonometry, Ocular; D014463:Ultrasonography