Which toric IOL formula best predicts postoperative astigmatic outcome?

21 Nov 2020

A new study has shown that using the Kane toric formula significantly enhances the prediction of postoperative astigmatic outcome in comparison to other modern toric intraocular lens (IOL) formulas analysed.

In this retrospective consecutive case series, the authors used a large database of toric IOL refractive outcomes to compare the accuracy of the Abulafia-Koch, the Barrett, the EVO 2.0, the new Holladay 2 with total surgical-induced astigmatism, the Kane, and the Næser-Savini power formulas among 823 eyes of 823 patients who had a toric IOL inserted during surgery.

One eligible eye from patients having uncomplicated cataract surgery with insertion of an Alcon SN6AT(2-9) IOL from one surgeon was eligible for inclusion. Either the IOLMaster 500 or 700 was used to measure both pre- and postoperative biometry. The predicted postoperative refractive astigmatism was calculated for each formula using vector calculation. The authors then compared this with the actual postoperative refractive astigmatism to give the prediction error.

The greatest proportion of eyes with a prediction error within ±0.50 dioptre was observed with the Kane formula (65.6 percent), followed by the Barrett formula (59.9 percent), Abulafia-Koch formula (59.5 percent), EVO 2.0 formula (58.9 percent), Næser-Savini formula (56.7 percent), and Holladay 2 formula (53.9 percent).

The Kane formula also displayed a statistically significantly lower mean absolute prediction error (p<0.001) and a markedly lower variance of the prediction error (p<0.01) relative to all other formulas. There was no statistically significant difference seen among the mean absolute prediction errors for the Abulafia-Koch, Barrett, and EVO 2.0 toric formulas.

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