Agreement And Repeatability Of Axial Length And Main Ocular Biometric Endpoints Between Vemos-Axl And Iolmaster 700 For The Vemos Project Software Validation.

The aim of this study was to evaluate the agreement and the intrasession repeatability of the axial length (AL) obtained by the topograph VEMoS-AXL, designed by CSO, likewise to compare the ocular biometric parameters provided by VEMoS-AXL and IOLMaster 700 (Zeiss). This way, validating the consistency of the biometric values collected from the device for the VEMoS project that will be used as inputs for the building of a virtual eye. It is an essential part in the European project “Virtual Eye Model System for personalized refractive surgery treatment” which will offer pre-operative analysis, decision support and the simulation of postoperative outcomes for refractive surgery thanks to the software developed by VISSUM and the device by CSO

Vissum Grupo Miranza, Alicante, Spain.

The study included 30 eyes of 30 patients (mean age of 37.9 ± 9.7 years) where healthy eye examinations were performed with VEMoS-AXL (CSO) and IOLMaster 700 (Zeiss). Ocular biometric endpoints were collected and compared.

The normality of the sample was confirmed by Kolmogorov-Smirnov test (p>0.05). The repeatability of 6 consecutive measurements of axial length provided by VEMoS-AXL was evaluated using the within-subject standard deviation (Sw), the intraclass correlation coefficient (ICC) and Oneway ANOVA analysis. The comparison of ocular biometric parameters between devices was performed using the Paired T-test considering a significance level of 0.05. The agreement between the two devices was carried out using Bland-Altman method.

The repeatability analysis of AXL revealed a Sw of 0.8 micron and an ICC of 1.00. Mean AL was 23.72±1.31 mm with VEMoS-AXL and 23.69±1.28 with IOLMaster, not appreciating statistical difference between both devices (p 0.355). ANOVA analysis showed absence of differences in the three parameters for consecutive measurements. However, the anterior chamber depth (ACD) and corneal central thickness (CCT) showed minimal statistical differences between devices (mean difference of CCT 3.1±6.7 mm, mean difference of ACD 0.13±0.04 mm, p<0.05) but presenting strong correlations between measurements (rho>0.90, p <0.001).

Both VEMoS-AXL and IOLMaster 700 provide consistent axial length measurements. High correlations for the ACD and CCT confirm similarities between values. Even though there exist statistical mean differences for CCT values, these are minor and can be due to the number of study samples taken.  The new device VEMoS-AXL considers the refractive indices of the cornea and stroma, this possibly being the reason for the statistical differences found for ACD parameters.