Comparison of Target Refraction with Optical Vs. Immersion Biometry with Ladi Adjustment using Barrett Universal II Formula after Phacoemulsification with Premium IOLs

Abstract

Purpose: The Barrett’s formula requires optical biometry inputs. The Ladi adjustment was designed to overcome this and use ultrasound (US) axial length (AXL) inputs into Barrett’s universal II formula. We compared the residual refractive error (RRE) with optical vs. ultrasound biometry with Ladi adjustment following phacoemulsification when all IOL powers were calculated using Barrett’s formula. Study Design: Prospective, randomised, double blinded study Methods: All adults undergoing routine phacoemulsification were recruited. The keratometry and AXL were randomly measured using either the IOL master 500 (IM500) or a combination of US biometry and Sirius topography. For the US measurements, 200 microns was added to the AXL (Ladi adjustment) and values were entered in the online Barrett’s calculator. The RRE (spherical equivalent – target refraction) was determined at 6 months. Results: We included 200 eyes of which 100 had IOL-power calculation using the IM500 and 100 using the Ladi adjustment of the US. The groups were comparable in baseline characteristics. The RRE was comparable in the two groups (-0.09+0.27D in US vs. -0.08+0.23D in IM500, p=0.90). The RRE was slightly higher in eyes with AXL>25mm (n=18 eyes, -0.21+0.33D in US vs. -0.07+0.17D in IM500), though this was not statistically significant (p=0.27). The preop BCVA (β= 0.06D, 95%CI= -0.5 to 0.13D, p=0.07) was the only factor marginally influencing RRE. Conclusion: The US biometry with the Ladi adjustment was as accurate as the IM500 and can be reliably used with the Barrett’s formula for IOL power calculations. Caution should be maintained at extremes of AXL.