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Repeatability of Pentacam peripheral corneal thickness measurements
Raul Martin1, Sven Jonuscheit2, Ana Rio-Cristobal3
1Instituto 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.
Purpose:
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.
