Agreement of Axial Length Measurements by Three Different Biometric Devices NC01-NC04
Dr. Arathi Roddam Simha,
Associate Professor, Department of Ophthalmology, CMC Schell Campus, Arni Road, Vellore-632001, Tamil Nadu, India.
Introduction: Accurate Intraocular Lens (IOL) power calculation is crucial for spectacle independence and patient satisfaction post cataract surgery. Of the various parameters measured to calculate IOL power, Axial Length (AL) is the most crucial. There have been several advances in AL measurement devices with the current gold standard being Optical Biometry (OB). However, OB cannot be used in all cases and hence the earlier Ultrasound (US) biometry continues to be relevant. It is however important to conduct agreement analysis with the gold standard to ensure accuracy of results in all cases.
Aim: To compare the AL measurements obtained by Tomey AL 4000 US biometer and pachymeter (Tomey US), built in US biometer of the Nidek AL Scan biometer (Nidek AL US), and the Nidek AL partial coherence interferometry optical biometer (Nidek AL OB).
Materials and Methods: This was a non-interventional cross-sectional observational study. Patients with immature cataract satisfying the inclusion criteria scheduled for surgery and undergoing biometry underwent AL measurements by the three methods. AL measurements obtained with the two US devices were compared with OB measurements and agreement analysis was done.
Results: A total of 98 eyes of 60 patients were studied. The average AL measured by the three devices were, 22.97Â±0.79 mm by Tomey US, 23.24Â±0.89 mm by the built in applanation US of Nidek AL US scan and 23.08Â±0.81 mm by the Nidek AL OB. The mean inter-device difference in AL between Tomey US and Nidek AL OB was -0.11Â±0.15 mm and 0.16Â±0.44 mm between Nidek US and Nidek OB. There was excellent correlation between the Nidek AL OB and the Tomey US, Interclass Correlation was (ICC)=0.98, 95% CI (0.95, 0.99). Bland Altman Plot analysis also showed high agreement between these two devices. About 94% of the values were within 0.3 mm difference between these two devices and there were no eyes with =1 mm difference.
Conclusion: There was excellent correlation of AL as measured by Nidek AL OB and Tomey US.