title: Repeatability and reproducibility of applanation resonance tonometry: a cross-sectional study.
abstract: BACKGROUND
  To assess repeatability (intra-observer variability) and reproducibility (inter-operator variability) of intraocular pressure (IOP) measurements with servo-controlled Bioresonator Applanation Resonance Tonometry (ART) and to evaluate possible influential factors.
  
  
  METHODS
  The study included 178 patients (115 glaucoma and 63 controls; one eye per subject). IOP was measured once with a Goldmann applanation tonometer (GAT) and twice by ART (ART1, ART2), in randomized sequence, by a single operator to assess intra-operator variability. Each ART measurement consisted on 3 readings. To assess inter-operator variability 2 evaluators performed 2 measurements each (in random order) on the same patient. Repeatability and reproducibility were assessed by the coefficient of variation (CoV) and intraclass correlation coefficient (ICC).
  
  
  RESULTS
  In the entire cohort, ART1 was 0.4 ± 2.2 mmHg (-7.0 to 5.7 mmHg) higher than ART2 (p = 0.03) regardless of test order. Intra-operator CoV was 7.0% ± 6.3%, and ICC was 0.80-0.92. Inter-operator CoV ranged between 5.7% ± 6.1% and 8.2% ± 7.2%, and ICC between 0.86 and 0.97. ART1 and 2 were respectively 1.7 ± 3.1 and 1.3 ± 3.1 mmHg higher than GAT (p < 0.01). Test-retest difference with ART fell within ±1 mmHg in 41% of cases, within ±2 mmHg in 70%, within ±3 mmHg in 85%. 15% had a test-retest difference higher than ± 3 mmHg; Bland-Altman 95% intervals of confidence were -3.9 and +4.6 mmHg. Results were unaffected by age, diagnosis, central corneal thickness, keratometry, operator, randomization sequence.
  
  
  CONCLUSIONS
  In most cases ART repeatability and reproducibility were high, with no differences due to patients' characteristics. ART measurements overestimated GAT by a mean of 1.3-1.7 mmHg.
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. laura.ottobelli@gmail.com.
authors.forename: Laura
authors.initials: L
authors.lastname: Ottobelli
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. fogagnolopaolo@googlemail.com.
authors.forename: Paolo
authors.initials: P
authors.lastname: Fogagnolo
authors.affiliation: Dipartimento di scienze oftalmologiche e neurochirurgiche, Università degli Studi di Siena, Siena, Italy. frezzottip@unisi.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Frezzotti
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. stefano_de_cilla@yahoo.co.uk.|Eye Clinic, Azienda Ospedaliero-Universitaria Maggiore della Carità, Novara, Italy. stefano_de_cilla@yahoo.co.uk.
authors.forename: Stefano
authors.initials: S
authors.lastname: De Cillà
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. elena.vallenzasca@virgilio.it.
authors.forename: Elena
authors.initials: E
authors.lastname: Vallenzasca
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. mauriziodigiuni@gmail.com.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Digiuni
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. doctorpaderni@email.it.
authors.forename: Ruggiero
authors.initials: R
authors.lastname: Paderni
authors.affiliation: Dipartimento di scienze oftalmologiche e neurochirurgiche, Università degli Studi di Siena, Siena, Italy. ilaria.motolese@libero.it.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Motolese
authors.affiliation: Dipartimento di scienze oftalmologiche e neurochirurgiche, Università degli Studi di Siena, Siena, Italy. bagasimo@gmail.com.
authors.forename: Simone Alex
authors.initials: SA
authors.lastname: Bagaglia
authors.affiliation: Dipartimento di scienze oftalmologiche e neurochirurgiche, Università degli Studi di Siena, Siena, Italy. motolese@unisi.it.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Motolese
authors.affiliation: Eye Clinic, Dipartimento di Scienze della Salute, San Paolo Hospital, University of Milan, Milan, Italy. luca.rossetti@unimi.it.
authors.forename: Luca
authors.initials: L
authors.lastname: Rossetti
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055815:Young Adult; D063171:Corneal Pachymetry; D003430:Cross-Sectional Studies; D005902:Glaucoma, Open-Angle / Q000175:diagnosis; D006068:Gonioscopy; D064368:Healthy Volunteers; D007429:Intraocular Pressure / Q000502:physiology; D015588:Observer Variation; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation / Q000592:standards; D014792:Visual Acuity / Q000502:physiology