title: The influence of refractive errors on IOP measurement by rebound tonometry (ICare) and Goldmann applanation tonometry.
abstract: OBJECTIVE
  To evaluate the effect of refractive errors and central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) by ICare rebound tonometer (RT), and its agreement with measurements by Goldmann applanation tonometer (GAT).
  
  
  METHODS
  Two observers measured the IOP by using RT and GAT in four groups of healthy volunteers with emmetropic (n = 78), hyperopic (n = 83), myopic (n = 87) and astigmatic (n = 79) eyes. Refraction was assessed by an autorefractometer. CCT was assessed by ultrasound pachymetry.
  
  
  RESULTS
  In all groups, no significant interobserver difference was seen in IOP values detected by both tonometers (Wilcoxon signed-rank test not significant). In all groups, IOP values were higher as measured by RT than by GAT (paired t-test p = 0.000): mean RT-GAT difference was higher in myopic eyes (+1.6 +/- 1.8 mmHg), and it was less than 1 mmHg in the other groups. RT-GAT difference was correlated to the refraction (p < 0.001), and it was greater when an higher IOP was detected by RT (significant correlation between RT-GAT difference and IOP by RT, p < 0.001). Compared with GAT values, the IOP readings by RT were greater than 2 mmHg in respectively 17.9% (emmetropic), 13.3% (hyperopic), 34.5% (myopic) and 7.6% (astigmatic) of the eyes. With both tonometers, in all groups the IOP values were correlated with CCT (p < 0.05), but the discrepancy between RT and GAT values was not related to CCT.
  
  
  CONCLUSIONS
  In all groups of subjects, higher IOP values were detected by RT; the IOP readings exceed the GAT values usually in a range of less than 1 mmHg, except when RT detects IOP >18 mmHg and generally in myopic eyes; RT-GAT discrepancy is related to the refractive error, but not to CCT.
authors.affiliation: Eye Clinic, University of Catania, via Clementi 36, Catania, 95154, Italy. t.avitabile@unict.it
authors.forename: Teresio
authors.initials: T
authors.lastname: Avitabile
authors.forename: Antonio
authors.initials: A
authors.lastname: Longo
authors.forename: Daniela
authors.initials: D
authors.lastname: Rocca
authors.forename: Roberta
authors.initials: R
authors.lastname: Amato
authors.forename: Caterina
authors.initials: C
authors.lastname: Gagliano
authors.forename: Marine
authors.initials: M
authors.lastname: Castaing
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000473:pathology; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011446:Prospective Studies; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000503:physiopathology*; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000379:methods*; D055815:Young Adult