Agreement in anterior segment measurements between swept-source and Scheimpflug-based optical biometries in keratoconic eyes: a pilot study

Abstract

Background: Cataract surgery in keratoconic patients is challenging because of the corneal distortion, which can lead to inaccurate keratometry readings. This study is a comparison of the accuracy of keratometry readings by two types of devices in a tertiary hospital. Purpose: To evaluate the comparability of corneal power measurements, anterior chamber depth (ACD), and white-to-white (WTW) distance between Scheimpflug-based tomography (Pentacam AXL; OCULUS GmbH, Wetzlar, Germany) and swept-source optical biometry (IOLMaster 700; Carl Zeiss Meditec AG, Jena, Germany) in patients with keratoconus. Methods: This pilot, prospective, interinstrument reliability study included 30 keratoconic eyes of 15 individuals who had not undergone any kind of corneal surgery. Standard K and total refractive power (TK®) of the flattest and steepest axes of the IOLMaster 700 were compared with the standard keratometry (SimK), true net power (TNP), equivalent keratometer readings (EKR), and total corneal refractive power (TCRP) of the Pentacam. The Bland–Altman analysis was used to evaluate the agreement between the measurements of both devices. The paired-samples t-test and the Wilcoxon signed-rank test were performed to compare the mean values of the variables obtained with the devices. Results: The K1 value of the IOLMaster 700 was significantly higher from EKR K1 along the 3-mm (mean difference: 0.79 diopters, p = 0.01), 4-mm (mean difference: 1.01 D, p = 0.01), and 4.5-mm zones (mean difference: 1.20 D, p = 0.01) and TNP K1 along the 3-mm (mean difference: 0.88 D, p < 0.001) and 4-mm zones (mean difference: 0.97 D, p < 0.001). The TK1 value was significantly higher from EKR K1 along the 2-mm (mean difference: 0.42 D, p = 0.04), 3-mm (mean difference: 0.83 D, p = 0.003), 4-mm (mean difference: 1.05 D, p = 0.004), and 4.5-mm zones (mean difference: 1.24 D, p = 0.005) and TNP K1 along the 3-mm (mean difference: 0.92 D, p < 0.001) and 4-mm zones (mean difference: 1.01 D, p < 0.001). The K2 value of the IOLMaster 700 was significantly higher from TK2 (mean difference: 0.11 D, p = 0.04) and all the corresponding variables of the Pentacam device. The TK2 value was significantly higher from all the corresponding variables of the Pentacam device. The Pentacam also yielded significantly lower values for the WTW distance (mean difference: 0.31 mm, p < 0.001) and no significant difference in terms of ACD values ( p = 0.9). Conclusion: The IOLMaster measured significantly greater keratometry readings in the steep axis for all the variables studied. The keratometry and WTW measurements of the investigated devices cannot be used interchangeably in keratoconus.

Comparison of Total Corneal Astigmatism between IOLMaster and Pentacam

“…Previous study had reported that Pentacam had large ACD values than IOLMaster [26]. Besides the difference of measuring mode, the measuring diameters also are different [27][28][29].…”

Cataract surgery considerations in patients with prior history of keratoconus and ectasia

“…Studies comparing keratometry measurements ( K f , K s , K m , K max ) of Pentacam HR and IOL Master showed no difference in values [27]. By contrast, comparisons of total K of IOLMaster to SimK, TCRP, and TNP of Pentacam AXL revealed that IOL Master results in significantly greater keratometry values and overestimates corneal power [23 ▪ ]. Comparisons of Pentacam HR and Lenstar in keratoconus patients reveal flatter K values with Pentacam [8,25,28].…”

“…Pentacam provides multiple measurements of corneal power, including simulated K (SimK), true net power (TNP), equivalent keratometry reading (EKR), and total corneal refractive power (TCRP). Studies comparing these parameters note that TCRP [5,23 ] and TNP [24] measure flatter values compared with SimK, whereas SimK values were significantly greater than EKR at increased corneal zone diameters [25].…”

Correction of Asymmetric Bowtie Corneal Astigmatism with a Toric Intraocular Lens: Outcomes and Accuracy of Measurement Modes

“…Another study showed that IOLMaster measured significantly greater keratometry readings in the steep axis for all participants. The keratometry and WTW measurements of the IOLMaster and Pentacam cannot be used interchangeably in keratoconic patients [ 18 ]. However, it is unclear which measurement mode is most accurate in the surgical planning of toric IOL implantation in eyes with asymmetric bowtie corneal astigmatism.…”