IOL Power Calculation After Radial Keratotomy Using the Haigis and Barrett True-K Formulas

To compare the accuracy of intraocular lens (IOL) power calculation in patients with previous radial keratotomy using the Haigis and Barrett True-K formulas.

In a retrospective cases series of patients with previous radial keratotomy and minimum follow-up of 1.2 months, preoperative data from an IOLMaster 500 or 700 (Carl Zeiss Meditec AG), the IOL power implanted, and the postoperative refraction were used to calculate the refractive prediction error. The primary outcomes were the mean absolute and arithmetic refractive prediction errors and the percentage of eyes with a refractive prediction error within ±0.50 and ±1.00 diopters (D).

One hundred eight eyes were evaluated with a mean follow-up of 6.9 ± 4.9 months. The Haigis formula yielded a mean arithmetic refractive prediction error of -0.29 ± 1.00 D, which was significantly different than that of the Barrett True-K formula, which was -0.03 ± 0.96 D (P < .001). The mean absolute refractive prediction error was 0.80 ± 0.67 for the Haigis formula and 0.74 ± 0.60 for the Barrett True-K formula (P > .05). The percentages of eyes with a refractive prediction error within ±0.50 and ±1.00 D were 43.5% and 65.7% for the Haigis formula and 42.6% and 75.9% for the Barrett True-K formula, respectively (all P > .05). The subgroup analysis revealed that for flat corneas (K1 < 38.00 D), the Barrett True-K formula resulted in more hyperopic results than the Haigis formula.

The Barrett True-K formula exhibited better arithmetic predictability than the Haigis formula; however, it showed a tendency for hyperopic results in very flat corneas. [J Refract Surg. 2020;36(12):832-837.].