SS-OCT biometers using the Sum- of-Segments method versus using the Mean Group Refractive Index to measure axial length – how does it affect IOL power calculations?

• Today’s SS-OCT biometers employ two methods to measure the axial length: Sum-of Segments using individual refractive indices or a Mean Group Refractive Index. 

• The differences in axial length measurement between the two methods are statistically significant and most noticeable in long and short eyes. 

• Axial length determined with the Mean Group Refractive Index is slightly shorter in short eyes and longer in long eyes.

• Depending on the length of the eye, some newer IOL power calculation formulas may provide better outcomes with the Sum-of Segment method.