[Precision of a new device for biometric measurements in pseudophakic eyes]

Biometric measurements and the knowledge of interrelationships of structures within the eye are especially mandatory for cataract and refractive surgery. As the number of pseudophakic patients steadily increases because cataract surgery becomes more easily available all over the world, exact biometry of eyes with crystalline lenses as well as pseudophakic eyes is gaining interest. In the present study we compared biometric measurements in pseudophakic eyes using a new optical low-coherence reflectometry (OLCR) device with results measured by the IOLMaster.

In this prospective study 140 pseudophakic eyes from 123 adult volunteers following uneventful cataract surgery and IOL implantation were examined at the International Vision Correction Research Centre (IVCRC) at the University of Heidelberg, Germany. The aim of this study was to evaluate a functional prototype of the new LENSTAR LS 900 (Haag-Streit)/ALLEGRO BioGraph (Wavelight) biometer and the IOLMaster V.5 (Carl Zeiss Meditec) and to compare axial length (AL) and keratometry measurements with those obtained by the IOLMaster. Additionally we investigated whether the LENSTAR/BioGraph can detect anterior chamber depth (ACD) and the effective lens position (ELP) of IOLs by OLCR in pseudophakic eyes. Patients with corneal or intraocular pathology and patients who had undergone other surgery in the investigated eye or whose cataract surgery dated back less than 4 weeks were not included in the study. Measurements were repeated with both devices as recommended by the manufacturers. Results were compared using Bland-Altman plots, Passing Bablok regression analysis and Pearson correlation calculations (MedCalc version 7.3.0.1).

Valid axial length measurements were available in 137 eyes. The mean values were 23.75 mm for both devices (SD±2.08 with the IOLMaster, ±1.7 with the LENSTAR/BioGraph). The mean corneal radius (R) was 7.7±0.27 mm (IOLMaster) vs. 7.74±0.29 mm (LENSTAR/BioGraph). Valid ACD measurements with the LENSTAR/BioGraph were achieved in 30% of all cases. In 98.6% of the eyes in which ACD was analyzed manually a mean ACD of 4.73±0.53 mm was found.

Both devices tested in this study showed a high correlation for AL and keratometry measurements. ACD measurements performed with the LENSTAR/BioGraph showed a measurable signal but the prototype calculated a value only in the minority (30%) of cases. This study showed that on the one hand the LENSTAR/BioGraph has the potential to be a reliable and useful machine for clinical everyday routine: This space and time-saving device includes several features which make it a patient and user friendly tool for diagnostics as well as screening. On the other hand we found that the software used in the prototype could be improved especially in order to identify IOLs and to measure reliable ACD values in pseudophakic patients. IOL surfaces did not generate sufficient interference signals in the LENSTAR/BioGraph and although the light reflected by the IOL surfaces was recognized by the device the software version used in this study did not generate numerical results for ACD.