Yeni Cihazlar Otomatize Keratometre Yerine Kullanılabilir mi? Lenstar ve OPD ile Karşılaştırılması

1. 1Selcuk University Faculty Of Medicine, Department Of Ophthalmology, Konya, Turkey
2. 2Dünya Göz Hospital, Istanbul, Turkey

Sorumlu Yazar: A precise keratometry measurement is essential ophthalmology practice. Although the traditional way of performing keratometry measurements was through manual keratometer, automated refractokeratometers are used practically. Today, many new devices are available for both corneal power calculations and for measurement of ocular dimensions. For example, the LenStar is an optical low-coherence reflectometer that is capable of performing keratometry and determining many other ocular components. This instrument can be used as a first-line tool to calculate the intraocular lens power for modern cataract surgery.7 These developments in ophthalmic technology, and the new devices that have come available, have prompted studies to compare these devices with the conventional ones, to determine the practicality of replacing older instruments with new technology. In the present study, keratometry results obtained with the LenStar were found to give values 0.12 diopters lower than the keratometry results obtained with the OPD Scan II and only 0.01D lower than the readings given by ARK. These differences were not statistically significant when the LenStar measurements were compared to those of the OPD Scan II and ARK. Savini et al.8 compared the keratometry results obtained with Scheimpflug camera imaging (Pentacam, Oculus, Germany), corneal topography, or partial coherence interferometer (PCI) for intraocular power calculations in cataract surgery. They reported that the Scheimpflug results were accurate, but the mean results were lower than the measurements with either corneal topography or PCI. In our study, we also obtained lower but not significantly different measurements with the LenStar than with corneal topography and ARK, in agreement with the results of Savini et al. Their mean corneal power measurements obtained with the Pentacam Scheimpflug system (software version 1.16) were not significantly different than their corneal topography measurements, but the agreement was poor. Modis et al.9 conducted a study about keratometry evaluations with the Pentacam high resolution (HR) and compared the results with automated keratometry and conventional topography. They reported statistically significant differences in keratometry measurements among Pentacam HR, automated keratometry and corneal topography systems and for patient follow-up, they recommended one certain keratometry device. We have found no significant difference in keratometry measurements among LenStar, automated keratometry and corneal topography (OPD) in our study. In the aforementioned study, they found automated keratometry to be the most repeatable. In our study, intraclass correlation was high among different examiners for ARK (78.9%), but the highest repeatability was found in corneal topography (OPD). The agreement between the three different devices in the manner of keratometry measurement was also high in our study (rho: 0.965-0.981). Shammas and Hoffer performed a study for repeatability and reproducibility of biometry and keratometry measurements with LenStar.10 They reported that the precision of the average K readings was high with an intraclass correlation (ICC) of 0.989. In our study, we have found an ICC of 0.997, regarding keratometry measurements with LenStar. The difference in the measurement of corneal power might be more significant when a toric or multifocal IOL is planned for implantation. The manufacturers recommend using manual keratometer when implanting toric IOLs, but the measured values might differ among different observers. Thus, it may be more convenient to perform corneal topography in native patients. The LenStar might be a better choice than OPD for measurement of corneal power in patients with a history of refractive surgery, as they have smaller optic zones.11 Reuland et al.12 compared the Pentacam and PCI for corneal curvature and stated that the difference observed is not clinically relevant and that the Pentacam could be used as a biometric device. Savini et al.8 proposed that the difference in overestimation and underestimation of corneal power with these devices could be compensated by constant optimization. In our study, for the comparison of K-values in diopter form, LenStar, OPD and ARK were set to the same keratometric index (1.3375, in all three devices). Since our study was designed to compare results of keratometry measurements, the values have not been used for intraocular lens calculation; but in case the mean keratometry values of ARK, OPD and LenStar were used in an IOL calculation formula (SRK-II) for error estimation hypothetically; with LenStar, the mean IOL power would be 0.01 and 0.12 diopters lower than obtained with ARK and OPD. This difference would again be not significant in clinical practice. However, the significance level of this difference should also be supported by clinical studies. Acar et al.13 compared the keratometry readings from keratometer, corneal topography and automated keratometer in keratoconus patients. They have reported that corneal topography measurements were flatter than with the other two methods. We have found similar results with ARK and corneal topography; however, our patients were healthy adults. Our study has some limitations, as our sample size is small due to the voluntary participation of the subjects from the outpatient clinics. Our subjects were also healthy and not candidates for cataract surgery or intraocular lens implantation. Therefore, intraocular power calculation and postoperative error assessment were not performed, but only a hypothetical IOL power error estimation was performed by the mean keratometric results. However, the current study provides preliminary data for our future studies. We can use our findings for better applications of contact lens procedures and corneal refractive operations, as a first-line screening. In conclusion, our study data showed good correlation, and no significant difference, between keratometry readings of the LenStar, the OPD Scan II, and ARK. Moreover, the repeatability of all devices was found high. Even though the differences between these devices were not significant, each one has its own operating principles and the field of utility, thus, we do not recommend them to be used interchangeably for keratometry measurements. Address for Correspondence/Yazisma Adresi: Bengü Ekinci Köktekir MD, Selcuk University Faculty of Medicine, Department of Ophthalmology, Konya, Turkey Gsm: +90 532 353 27 16 E-posta: benguekinci@hotmail.com Received/Gelis Tarihi: 23.09.2012 Accepted/Kabul Tarihi: 23.11.2012