JUL 24, 2013
This retrospective study found that ray tracing based on biometry data improved IOL prediction accuracy compared with conventional formulas in normal eyes implanted with aberration-correcting IOLs. The authors also found that the number of outliers with greater prediction errors can be reduced significantly. Maybe we will have new formulas with ray tracing to improve outcomes soon.
They reviewed the charts of 185 patients implanted with three different aberration-correcting IOLs. Before surgery, axial length, corneal thickness, anterior chamber depth, crystalline lens thickness and corneal radii were measured with the Lenstar biometer. Subjective refraction was measured one month after surgery.
They found that the median absolute error was 0.28 D using the Hoffer Q formula, 0.27 D with the Holladay, 0.28 D with the SRK/T, and 0.24 D using ray-tracing calculation. With the ray-tracing calculation, 95 percent of eyes were within ± 0.71 D of the predicted refraction as opposed to ±0.85 D with the Hoffer Q, ±0.82 D with the Holladay and ± 0.84 D with the SRK/T.
They say that IOL calculation relying on physical data as much as possible is preferable to the classic formulas that have served us so well for more than two decades. They conclude that ray tracing overcomes some systematic errors and limitations of Gaussian optics, whereas Lenstar anterior chamber and lens thickness data simultaneously allow improved prediction accuracy of the axial length position, one of the single largest errors remaining in IOL calculation.