Repeatability of scheimpflug based corneal tomography parameters in advanced keratoconus with thin corneas

Abstract

Objective To determine the repeatability limits of corneal tomography parameters in patients with advanced and moderately thin keratoconic corneas to assist in planning thickness-based procedural interventions. Methods Prospective, single-centre, repeatability study. Three tomography scans using the Pentacam AXL were obtained from patients with keratoconus with thinnest corneal thickness TCT ≦ 400 µm (sub-400 group) and compared to those with TCT = 450–500 µm (450-plus group). Eyes with previous crosslinking, intraocular surgery, or acute corneal hydrops were excluded. Eyes were age and gender-matched. The within-subject standard deviations for flat keratometry (K1), steep keratometry (K2), maximal keratometry (Kmax), astigmatism and TCT were used to calculate respective repeatability limits (r). Intra-class correlation coefficients (ICC) were also analysed. Results The sub-400 group comprised 114 eyes from 114 participants, and the 450-plus group comprised 114 eyes from 114 participants. In the sub-400 group, TCT was amongst the least repeatable parameters (33.92 µm; ICC 0.96), compared with the 450-plus group (14.32 µm; ICC 0.99, p < 0.01). In the sub-400 group, K1 and K2 of the anterior surface were the most repeatable parameters (r 3.79 and 3.22 respectively; ICC 0.97 and 0.98 respectively) compared with the 450-plus group (r 1.17 and 0.92 respectively; and ICC 0.98 and 0.99 respectively, p < 0.01). Conclusions The repeatability of corneal tomography measurements is significantly reduced in sub-400 keratoconic corneas when compared to 450-plus corneas. Consideration to repeatability limits should be carefully considered when surgical interventions are planned for such patients.

Comparing Repeatability and Agreement between Commonly Used Corneal Imaging Devices in Keratoconus

“…Although the eyes included in this study had a spectrum of keratoconus severity, measurements have been shown to have greater fluctuation with increasing severity. 21 In addition, some subjects may not have been out of contact lenses long enough before the scan, so the effect of contact lens use on the measured parameters must be taken into account, and thus, this study's findings may not apply to other groups of patients.…”

Corneal Tomography in a Commercially Available Optical Coherence Tomography Device and Comparison With a Rotating Scheimpflug Camera

“…It is also known that the repeatability of corneal tomography measurements is significantly reduced in patients with advanced keratoconus and corneas thinner than 400 mm when compared with individuals with corneas thicker than 450 mm. 23 Moreover, the variability of measurements can be an indicator of clinical progression of keratoconus. 24 The present investigation showed a relatively large difference between the devices in corneal thickness measurements; for Revo, the values were significantly lower than for Pentacam AXL (535.54632.45 vs. 550.74631.55 mm), and this difference was even greater for thinnest pachymetry.…”

“…It is also known that the repeatability of corneal tomography measurements is significantly reduced in patients with advanced keratoconus and corneas thinner than 400 μm when compared with individuals with corneas thicker than 450 μm. 23 Moreover, the variability of measurements can be an indicator of clinical progression of keratoconus. 24…”

Multi-modal imaging for the detection of early keratoconus: a narrative review

“…The difference in measurements between different devices were statistically significant, and therefore should not be used interchangeably. Additionally, the repeatability may be affected according to the status of the measured cornea (i.e., healthy corneas, KC severity, thin corneas) [34].…”