title: Repeatability of Pentacam peripheral corneal thickness measurements.
abstract: OBJECTIVE
  To assess the repeatability of corneal thickness (CT) measurements, along the horizontal meridian up to 5mm from centre, in healthy eyes with the Pentacam instrument.
  
  
  METHODS
  CT was measured in 82 right eyes (82 healthy subjects) at 11 corneal locations nominally 1mm apart along the horizontal meridian with Scheimpflug topography Pentacam. Two consecutive scans were performed in quick succession. The repeatability of CT was determined by assessing differences between measurements and calculating the coefficient of variation (CV). The relative repeatability (difference) was calculated as the ratio of the absolute peripheral CT difference to the central thickness. A variant of Bland-Altman analysis was carried out to determine the effect of the overall magnitude of CT on the absolute and relative differences.
  
  
  RESULTS
  Mean CT (μm) at the temporal 5mm location was 770 ± 51 and 823 ± 56 μm at the corresponding nasal location; central CT was 554 ± 36 μm. Good repeatability (CV < 1.2%) was found at all corneal locations. Differences (arithmetic; absolute and relative) were 3 ± 17 μm; 13 ± 11 μm; 2 ± 2%; respectively temporally and -1 ± 15 μm; 13 ± 8 μm; 2 ± 1% nasally, both at 5mm from the corneal apex. These values decreased for central CT (0 ± 6 μm; 4 ± 4 μm; 1 ± 1%). Differences between both measurements in all corneal locations were not statistically significant (p = 0.308 ANOVA Games-Howell).
  
  
  CONCLUSIONS
  Pentacam shows good repeatability for pachymetry measurements up to 5 mm away from the corneal apex across the horizontal meridian, even though repeatability decreases slightly towards the periphery. A single Pentacam scan will be sufficient for most clinical applications.
authors.affiliation: Instituto Universitario de Oftalmobiología Aplicada (IOBA - Eye Institute), Universidad de Valladolid, Paseo de Belén, 17 - Campus Miguel Delibes, 47011 Valladolid, Spain; Departamento de Física Teórica, Atómica y Óptica (School of Optometry), Universidad de Valladolid, Paseo de Belén, 7 - Campus Miguel Delibes, 47011 Valladolid, Spain; Department of Life Sciences, Glasgow Caledonian University (GCU), Glasgow, Scotland, UK. Electronic address: raul@ioba.med.uva.es.
authors.forename: Raul
authors.initials: R
authors.lastname: Martin
authors.affiliation: Instituto Universitario de Oftalmobiología Aplicada (IOBA - Eye Institute), Universidad de Valladolid, Paseo de Belén, 17 - Campus Miguel Delibes, 47011 Valladolid, Spain; Department of Life Sciences, Glasgow Caledonian University (GCU), Glasgow, Scotland, UK; Anterior Eye Research Group, Institute for Applied Health Research, Glasgow Caledonian University (GCU), Glasgow, Scotland, UK.
authors.forename: Sven
authors.initials: S
authors.lastname: Jonuscheit
authors.affiliation: Instituto Universitario de Oftalmobiología Aplicada (IOBA - Eye Institute), Universidad de Valladolid, Paseo de Belén, 17 - Campus Miguel Delibes, 47011 Valladolid, Spain; Departamento de Física Teórica, Atómica y Óptica (School of Optometry), Universidad de Valladolid, Paseo de Belén, 7 - Campus Miguel Delibes, 47011 Valladolid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Rio-Cristobal
authors.affiliation: Department of Life Sciences, Glasgow Caledonian University (GCU), Glasgow, Scotland, UK; Anterior Eye Research Group, Institute for Applied Health Research, Glasgow Caledonian University (GCU), Glasgow, Scotland, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Doughty
mesh_terms: D000328:Adult; D063171:Corneal Pachymetry / Q000295:instrumentation / Q000592:standards*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D016850:Limbus Corneae / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D015203:Reproducibility of Results; D055815:Young Adult
keywords: Human cornea; Pentacam; Peripheral corneal thickness; Repeatability; Scheimpflug pachymetry