Postoperative astigmatism errors by two toric intraocular lens calculation formula using anterior segment optical coherence tomography

<p> 【Purpose】Anterior segment optical coherence tomography (AS-OCT) has two methods for toric intraocular lens (T-IOL) calculation: the Barrett toric formula (BT formula) based on keratomerty (K) and the CASIA2 toric formula (CT formula) based on Fourier real power cylinder (FRCyl). We compared the postoperative astigmatism errors obtained using both formulas.</p><p> 【Subjects and Methods】Subjects were 39 eyes of 39 patients (20 males and 19 females; mean age, 68.8±9.7 years) who were implanted with multifocal T-IOL (ACTIVEFOCUSTM SV25T3-6, Alcon). The T-IOL power was determined using the CT formula in all eyes at the time of surgery. We retrospectively examined the following: 1) comparisons of the preoperative corneal with-the-rule (WTR) and against-the-rule (ATR) astigmatic measurements obtained using the K and FRCyl values, and 2) comparisons of the postoperative astigmatism errors and the percentages of eyes that had achieved a refractive astigmatism error within ±0.50 D and ±1.00 D with both formulas.</p><p> 【Results】The degree of the preoperative corneal ATR astigmatism obtained with FRCyl was significantly higher (p = 0.04). The respective mean postoperative WTR and ATR astigmatism errors were 0.64±0.36 D (the BT formula) and 0.45±0.39 D (the CT formula) (p = 0.18); and 0.37±0.27 D (the BT formula) and 0.36±0.29 D (the CT formula) (p = 0.84). No significant difference was seen between the values obtained by both formulas. The percentages of eyes that had achieved a refractive astigmatism error within ±0.50 D were 66% with both formulas (p = 0.59); and the percentages for those achieving within±1.0 D were 90% with the BT formula and 95% with the CT formula (p = 0.67). No significant difference was seen between these percentages.</p><p> 【Conclusion】The CT formula installed on the AS-OCT showed the same astigmatism correction effect as same as the effect by the BT formula. T-IOL with power calculated using the CT formula installed on the AS-OCT could achieve the same astigmatism correction effect as that using the BT formula.</p>