Comparison of Pentacam Scheimpflug Camera with Ultrasound Pachymetry and Noncontact Specular Microscopy in Measuring Central Corneal Thickness

Abstract

Purpose: Although central corneal thickness (CCT) can be measured by several methods, interchangeability of different modalities has not been fully investigated. CCT is known to correlate with intraocular pressure (IOP). The aim of this study was to evaluate the agreement of Pentacam Scheimpflug system with noncontact specular microscopy (NCSM) and ultrasound (US) pachymetry in measuring CCT and the relation between IOP taken with Goldmann applanation tonometer (GAT) and the CCT measured with these three methods. Methods: The right eyes of 135 enrolled persons without antiglaucoma drug use (100 females and 35 males), who comprised 32 patients with primary open-angle glaucoma, 14 with ocular hypertension, 45 with primary angle-closure glaucoma, and 44 controls, were studied. Intermethod comparison of CCT was made by the 95% limits of agreement analysis according to Bland and Altman. Linear regression analysis was used to assess the relationship between IOP and CCT taken with each modality. Results: The mean CCT (±SD) taken with Scheimpflug, US, and NCSM was 559.49 ± 38.44 μ m, 553.01 ± 39.33 μ m, and 552.04 ± 42.95 μ m, respectively. The average values of CCT taken with the three instruments were not significantly different (one-factor ANOVA; p = 0.26), although the marginal mean difference between Scheimpflug and US or NCSM was statistically significant (paired t test; p = 0.0009 and 0.005, respectively). The 95% limits of agreement were 6.47 ± 43.21 μm between Scheimpflug and US, 7.45 ± 58.86 μ m between Scheimpflug and NCSM, and 0.98 ± 51.69 μ m between US and NCSM. There was a positive association between IOP and CCT measured with US or NCSM, whereas there was no correlation between IOP and CCT measured with Scheimpflug. Conclusions: Although CCT values measured with Scheimpflug, US, and NCSM are closely similar, clinicians should keep in mind that these methods are not simply interchangeable.

KEYWORDS:

• central corneal thickness
• interchangeability
• noncontact specular microscopy
• Scheimpflug camera
• ultrasound pachymetry