Date Published: February 27, 2018
Publisher: Public Library of Science
Author(s): Yanjun Hua, Wei Qiu, Qiuyi Xiao, Qiang Wu, Manuel Garza León.
To assess the precision (repeatability and reproducibility) of ocular parameters measured by the Tomey OA-2000 biometer, and to compare them with those measured by the IOLMaster.
In this prospective study, the right eyes of 108 healthy subjects were included. Three consecutive scans were obtained by 2 observers using the Tomey OA-2000, and in the same session one observer used the IOLMaster (version 5.4.4.0006) for the measurements. About 1 week later, 3 scans were obtained by one observer using the Tomey OA-2000. The axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), keratometer readings, pupil diameter (PD) and corneal diameter (CD) values measured by the Tomey OA-2000 and IOLMaster were analyzed. The coefficient of variation (CoV), intraclass correlation coefficient (ICC), within subject standard deviation (Sw) and 2.77Sw were calculated to assess the repeatability and reproducibility. The paired t test and Bland-Altman plots were used to analyze the differences and agreements of parameters measured by the two devices, respectively.
Intraobserver repeatability, and interobserver and intersession reproducibility of the AL, CCT, ACD, LT, Kf, Ks, Km, PD and CD values measured by the Tomey OA-2000 biometer showed a CoV of less than 1% except that for PD, and an ICC of more than 0.97 except that for PD and CD. The AL, Kf, Ks, Km and CD values measured by the Tomey OA-2000 were 0.058 ± 0.094 mm, 0.088± 0.150 diopters (D), 0.163 ± 0.170 D, 0.127 ± 0.117 D and 0.171 ± 0.217 mm lower than those measured by the IOLMaster, respectively (all Ps < 0.05). However, the ACD values from the two devices were comparable (P = 0.169). The 95% linite of agreement (LoA) of the AL, ACD, CD and all keratometer readings were no more than 0.24 mm, 0.14 mm 0.60 mm and 0.5 D, respectively. Except for the PD and CD, the ocular parameters measured by the Tomey OA-2000 were highly repeatable and reproducible. Except for the CD value, there was good agreement of ocular parameters measured by the Tomey OA-2000 and the IOLMaster in healthy eyes.
Accurate ocular biometry is essential for predicting the intraocular lens (IOL) power before refractive and cataract surgery. Generally for cataract surgery, precise ocular biometry can decrease refractive error and achieve the predicted postoperative outcome. Ultrasound-based axial length (AL) and anterior chamber depth (ACD, from corneal epithelium to anterior surface of crystalline lens) measurements have been the benchmark for a long period of time. However, the contact measurement is accompanied by the risk of infection and indentation compelling technicians and clinicians to seek safer and more comfortable techniques for ocular biometry. In 1999, the introduction of the partial coherence interferometry (PCI) based IOLMaster (Carl Zeiss Meditec AG) marked a great improvement due to its non-contact nature and higher resolution of AL measurement (about ±0.02 mm compared to ±0.15 mm by ultrasound)[2–4]. Furthermore, the inclusion of the corneal curvature, ACD and horizontal corneal diameter (CD) measurements in the same device, minimized the time for all measurements and improved the calculation of IOL power. In the last decade, the precision of the IOLMaster in both cataract biometry[5–7] and the study of refractive error evaluation[8, 9] set a new standard for ocular biometry. However, only AL measurement is based on PCI principle for the IOLMaster. The corneal curvature, ACD and CD are obtained from image analysis. Nevertheless, in IOLMaster 500 and older models, such as the model(software version: 5.4.4.0006) used in the present study, the corneal, crystalline lens or retinal thickness are not evaluated. Additionally, realignment is required before each parameter is measured.
The study was conducted between July and September 2015 at the Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital. The study protocol followed the principles of the Declaration of Helsinki and was approved by the Office of Research Ethics Committee, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital. All subjects provided written informed consent after the purpose of the study had been explained to them in detail.
With the development of phacoemulsification and IOL implantation in cataract and refractive lens surgery, accurate ocular biometry is essential for achieving the predicted postopervative refractive outcomes. In the present study, we evaluated the precision of ocular parameters measured by the Tomey OA-2000 biometer and found excellent intraobserver repeatability and interobserver and intersession reproducibility for all parameters except for PD and CD. Moreover, we compared the AL, keratometer readings, ACD and CD measured by the new device with those measured by the IOLMaster and found that the differences were very small but statistically significant.