Refractive Predictability Of Iol Calculations Using Segmental Versus Single Refractive Indices For Axial Length Measurements

To compare the refractive predictability of a combined SS-OCT/reflection biometer which uses segmental refractive indices for axial length (AL) calculations to another SS-OCT biometer and an OLCR biometer which use single refractive index in short (AL<22,5 mm), normal and long eyes (AL>25mm).

This was a retrospective study of uneventful cataract surgery. Refractive prediction was compared between a combined SS-OCT/reflection biometer which uses a sum of segments approach for axial length (Argos, Alcon), an OLCR biometer (Lenstar 900, Haag Streit) and another SS-OCT biometer (Anterion, Heidelberg Engineering). The IOL calculations were performed with the Barret Universal II formula, and initial IOL selection was based on the OLCR biometer. The primary outcome measures were the refractive prediction error (RPE) and MedAE (median absolute error with arithmetic mean error reduced to zero) 4-6 weeks after surgery. Secondary outcome measures were refractive spherical equivalent and visual acuity.

129 Eyes of 129 patients were included, 57% were female and mean age was 75 years. The mean logMAR UCVA was 0.1. The mean refractive SE was -0.04 D. The Argos showed lower arithmetic RPE compared to the Anterion in both the short eyes( 0.13 vs -0.32, respectively) and the normal eyes group (0.07 vs -0.13, respectively) (p=0.01), and to the Lenstar in the normal (0.07 vs 0.18, respectively) and the long eyes group(-0.05 vs 0.22) (p<0.01). The medAE was lowest for Argos in the short eyes group, and for the Lenstar in the normal and long eyes group, but this was not statistically different. No statistically significant differences in percentages of eyes within 0.5 D, 0.75 D or 1 D were observed.

The Argos showed the lowest RPE compared to the Anterion in short and normal eyes and compared to the Lenstar in normal and long eyes. However, the MedAE was not significantly different between the devices. The refractive predictability of a combined  SS OCT/reflection biometer with sum of segments approach appear to be comparable with that of another SS OCT and an OLCR biometer which use single refractive index for AL measurements.