Interocular differences of the Pentacam measurements in normal subjects

Abstract

Purpose:The aim of this study was to determine the interocular differences of the Pentacam corneal measurements in a normal population. Methods: A retrospective analysis was performed on 550 eyes of 275 consecutive subjects evaluated for refractive surgery at the Rassoul Akram Hospital, Iran University of Medical Sciences. A Pentacam Scheimpflug camera was used for corneal measurements. Statistical analysis was performed to determine the normal levels of the difference between the two eyes. Results: One hundred and four men and 171 women with a mean age of 29.1 Ϯ 7.73 years were evaluated. The mean (range) interocular difference was 2.17 (zero to 21) mm for maximum anterior elevation (AEmax), 3.62 (zero to 31) mm for maximum posterior elevation (PEmax), 8.42 (zero to 30) mm for minimum corneal thickness (CTmin), 0.06 (zero to 0.4) mm 3 for three millimetre corneal volume (CV3), 0.19 (zero to 1.2) mm 3 for five millimetre corneal volume (CV5), 0.44 (zero to 2.9) mm 3 for seven millimetre corneal volume (CV7), 0.24 (zero to 2.5) dioptres for the mean keratometry (Km) and 0.39 (zero to 2.5) D for measurements of the corneal dioptric power in the steepest meridian (Kmax). Conclusions: Individuals with differences greater than 17.4 mm in AEmax, 29.1 mm in PEmax, 29.6 mm in CTmin, 2 D in Km, 2.27 D in Kmax, 0.32 in CV3, 1.05 in CV5, and 2.6 in CV7 between eyes represent less than 0.5 per cent of the population. An interocular difference outside the normal range should alert the clinician to examine for other parameters that are more predictive of post-refractive surgical ectasia.

Intereye Asymmetry Detected by Scheimpflug Imaging in Subjects With Normal Corneas and Keratoconus

“…Distance was the only variable that did not show statistically significant difference between the better and worse eyes of the keratoconic patients (P = 0.22). The mean intereye asymmetry in volume at 3 mm central in the normal group was 0.07 mm 3 , similar to 0.06 mm 3 reported in a previous study, 25 and in the keratoconus group 0.15 mm 3 , demonstrating that there is a greater intereye asymmetry in the keratoconus group consistent with the characteristics of keratoconus as a bilateral, asymmetric, slowly progressive disorder in which the cornea has central or paracentral thinning, 1 resulting in asymmetry of the corneal volume.…”

“…When evaluating posterior elevation, the mean intereye asymmetry in the normal group at the posterior corneal elevation was 3.75 mm in accordance with 3.62 mm reported by Falavarjani et al, 25 at the maximum posterior elevation; and the mean intereye asymmetry in the keratoconus group was 20.08 mm. A cutoff value of 6.5 mm in the mean intereye asymmetry at the posterior elevation had an AUROC value of 0.91, with 85% sensitivity and 88% specificity, discriminating these 2 groups.…”

“…The mean intereye asymmetry in the normal group in pachymetry at the apex of the cornea was 10.28 mm, and at the TP was 11.04 mm, in accordance with those reported by Khachikian et al, 24 who reported 8.8 and 9.0 mm, respectively. Falavarjani et al 25 reported an intereye asymmetry of 8.42 mm at the TP for normal subjects. In contrast, our results show that the mean intereye asymmetry in the keratoconus group at the apex of the cornea was 25.89 mm and at the TP 30.15 mm.…”

Correlation of Corneal Elevation With Severity of Keratoconus by Means of Anterior and Posterior Topographic Analysis

“…Previous reports addressed the elevation of the posterior corneal surface to provide diagnostic cues as an earlier sign of keratoconus. [16][17][18] In the present study, ROC curve analyses with reference to keratoconic staging according to the Amsler-Krumeich classification indicated that the AUC did not differ significantly between anterior and posterior corneal surfaces in advanced keratoconus, whereas the assessment of posterior elevation was most important for the early detection of keratoconus. A combination of the curvature map and height data has promise for an improvement in diagnostic accuracy.…”

Anterior Segment Eye Assessment of Refractive Surgery Candidates in the Southeast of Iran

“…First, the assessment of corneal refractive parameters allows examiners to have more control over refractive error progress. CCT considered as a major factor in keratoconus diagnosis (Falavarjani et al, 2010;Fahd et al, 2014), precise IOP measurement, and early detection of open-angle glaucoma (Channa et al, 2009). Anterior chamber parameters could be helpful to IOL power calculation of cataract patients (Shankar et al, 2007).…”