Repeatability of peripheral (near-limbal) corneal thickness measurements of Pentacam Scheimpflug corneal topography

Abstract

Purpose: To assess the repeatability of peripheral corneal thickness (CT) measurements along the horizontal meridian as close to the limbus as possible in healthy eyes with Scheimpflug topography Pentacam.

Methods: CT was measured in 63 corneas of 63 healthy subjects at eleven corneal locations nominally 1 mm apart along the horizontal meridian with Scheimpflug topography Pentacam. Two consecutive Scheimpflug scans were performed in quick succession to determine the repeatability of the pachymetry values measured in each corneal location up to 5 mm away from the corneal apex. Ocular assessments also included habitual visual acuity, slit-lamp biomicroscopy, and optical coherence tomography. To rule out corneal endotheliopathy non-contact specular microscopy was performed. Descriptive statistics were generated. The repeatability was determined by assessing absolute differences between measurement 1 and 2. The relative difference was then calculated and expressed as the ratio of the absolute difference to the central CT. A variant of Bland-Altman analysis was carried out to determine the effect of the overall magnitude of CT on the differences between pachymetry measurements.

Results: The mean [SD] age was 27 [7] years. CT increased progressively and asymmetrically from the corneal center to the periphery. Mean CT (µm) at the temporal 5 mm location was 771 [49] and 823 [53] at the corresponding nasal location; central CT was 558 [33]. Peripheral CT repeatability, based on absolute differences (microns) between 2 measurements was 2.41 [13.41] temporally and -1.03 [15.39] nasally, both at 5 mm away from the corneal apex. These values decreased to just 0.27 [5.33] for central CT. This difference in repeatability between peripheral and central locations was not statistically significant (p=0.918 Kruskal-Wallis ANOVA, nasal and temporal). Regression analyses indicate that differences between measurements (repeatability) were not dependent on the absolute thickness values (p=0.978; r= 0.10).

Conclusions: Pentacam shows excellent repeatability not only for central pachymetry measurements near the corneal apex, but also for peripheral measurements close to the corneal limbus 5 mm away from the corneal centre in normal eyes. The results provide evidence of the utility of Pentacam assessment of the peripheral cornea in extended contact lens wear and surgical procedures.

Keywords: 479 cornea: clinical science • 421 anterior segment • 681 refractive surgery: corneal topography