### Materials and Methods

_{m}) (Fig. 1). The built-in software of the Visante AS-OCT automatically CH

_{m}when the posterior corneal surface and the intersection point of the angle and the corneal vertex lines were specified. All AS-OCT examinations were performed by one examiner.

_{real}) was calculated using actual IOL power and postoperative spherical equivalent.

_{est}) and measured ELP (ELP

_{m}). We compared several linear regression formulas between ELP

_{est}and ELP

_{m}in various options, based on K or adjusted K, through the SRK/T formula. Thereafter, we selected the best-fit regression formula based on a high correlation coefficient (R) and statistical significance. Second, we evaluated the clinically relevant efficacy of the selected regression formula. Converted ELP (ELP

_{conv}) and IOL power (P

_{conv}), obtained with the selected regression and SRK/T formulas, were compared with ELP

_{est}and P

_{real}, respectively. In addition, mean error and mean absolute error between P

_{conv}and P

_{real}were examined. Finally, we compared the accuracy of our method with those previously documented and assessed method feasibility. Our calculations were performed with the following assumptions.

_{const}) was defined as the A-constant (A) of each IOL using the following formula: ELP

_{const}= 0.62467 × A - 68.747.

_{const}- 3.336.

_{m}was calculated as follows: ELP

_{m}= CH

_{m}+ offset.

_{est}) was back-calculated using P

_{real}, AL, and K, through the SRK/T formula. For back-calculations, we assumed that 1.00 diopter (D) of IOL prediction error produces 0.70 D of refractive error at the spectacle plane [4,16,24]. The IOL Master was also used to back-calculate ELP

_{est-master}from parameters K

_{master}and AL

_{master}. In addition, we evaluated the change of the ELP predicting accuracy in this method when we used adjusted K obtained by several IOL calculation methods after refractive surgery. After keratometric values were adjusted according to the Wang-Koch-Maloney method [9], the Orbscan II central 2-mm total-mean corneal power method [25], and the Savini no-history method [14], each estimated ELP (ELP

_{Wang}, ELP

_{Orbscan}, ELP

_{Savini}) value was back-calculated with P

_{real}, AL, and each adjusted K (K

_{Wang}, K

_{Orbscan}, K

_{Savini}) with the SRK/T formula. To investigate the relationship between estimated ELP obtained with various formulas using ELP

_{m}, AL, and K, a stepwise linear regression was performed using IBM SPSS ver. 21.0 (IBM Corp., Armonk, NY, USA). This included ELP

_{est}, (calculated with ELP

_{m}, AL, and K), ELP

_{est-master}(calculated with ELP

_{m}, AL

_{master}, and K

_{master}), ELP

_{Wang}(calculated with ELP

_{m}, AL, and K

_{Wang}), ELP

_{Orbscan}(calculated with ELP

_{m}, AL, and K

_{Orbscan}), and ELP

_{Savini}(calculated with ELP

_{m}AL, and K

_{Savini}), as shown in Table 1 [9,14,26]. Of these, the best-fit formula was selected for IOL power prediction. The following selected regression formula was used: ELP

_{est}= 1.841 × ELP

_{m}- 2.018 (

*p*= 0.023, R = 0.410).

_{conv}values were obtained by applying ELP

_{m}to this selected regression formula. Additionally, P

_{conv}was calculated from ELP

_{conv}, AL, and K with the SRK/T formula. Agreement between ELP

_{conv}and ELP

_{est}and between P

_{conv}and P

_{real}is represented by Bland-Altman plots and expressed in terms of mean bias ±1.96 standard deviations (SD). The difference between P

_{conv}and P

_{real}was defined as the mean error; the absolute value of mean error was defined as the mean absolute error. The proportion of eyes within ±0.5, ±1.0, ±1.5, and ±2.0 D of the predicted refractive error was investigated when P

_{conv}was applied. Four additional methods were used to calculate IOL power for the comparison: 1) Orbscan II central 2-mm total-mean corneal power method + double-K method and the SRK/T formula; 2) Orbscan II central 2-mm total-mean corneal power method + double-K method and the Hoffer Q formula; 3) Shammas no-history method + double-K method and the SRK/T formula; 4) Savini no-history method + double-K method and the SRK/T formula. Preoperative corneal power used in the double-K method was substituted with 43.5 D, a value close to the mean of the study population.

*p*< 0.05.

### Results

_{est}, and ELP

_{m}were 3.71 ± 0.23, 7.74 ± 1.09, and 5.78 ± 0.26 mm, respectively. The number of eyes that had undergone PRK, LASIK, and LASEK were 9, 20, and 1, respectively. Four different IOL types were implanted, including the Alcon IQ SN60WF (n = 18 eyes), the Alcon Acrysof 1 piece SA60AT (n = 1 eye), the AMO Tecnis ZCB00 (n = 9 eyes), and the AMO Sensar AR40e (n = 2 eyes). Mean ELP

_{est}was 7.74 ± 1.09 mm and the best linear regression formula (Fig. 2) was, ELP

_{est}= 1.841 × ELP

_{m}- 2.018.

_{conv}was 7.74 ± 0.43 mm. Agreement between ELP

_{m}and ELP

_{est}is displayed in Fig. 3. The difference between ELP

_{m}and ELP

_{est}was -0.0021 ± 1.00 mm (mean ± 1.96 SD; range, -1.97 to 1.62 mm). Agreement between P

_{conv}and P

_{real}is displayed in Fig. 4. The difference between P

_{conv}and P

_{real}was 0.90 ± 1.24 D (mean ± 1.96 SD; range, -1.14 to 3.17 D) (Fig. 4). The mean absolute error was 1.27 ± 0.83 D (range, 0.03 to 3.17 D). Figs. 3 and 4 show considerable agreement between ELP

_{m}and ELP

_{est}, and P

_{conv}and P

_{real}, respectively. The percentages of eyes within ±0.5, ±1.0, ±1.5, and ±2.0 D of the refractive error were 23.3%, 66.6%, 83.3%, and 100.0%, respectively (Table 3) [4,16,25]. These percentages were compared to those calculated with the four additional methods and in another study [25] (Table 4). We found that our method provided relatively similar results compared to others.

### Discussion

*p*< 0.001). It is known that actual CH is closely related to anterior chamber depth (ACD) [27] and that ELP is significantly correlated with ACD [28]. Therefore, actual CH can be also related to ELP.

_{conv}and ELP

_{conv}showed good agreement with P

_{real}and ELP

_{est}, respectively. In comparing the accuracy of IOL power calculation for eyes with a history of myopic refractive surgery, our methods showed comparable accuracy with other conventional methods (Table 4). We chose the Shammas no-history, Savini no-history, and Orbscan II central 2-mm total-mean corneal power methods for K value modification because they have been relatively accurate in our clinical experience. McCarthy et al. [32] and Arce et al. [25] reported that 80.9% and 97.7% of eyes and 77% and 96% of eyes were within ±1.0 and ±2.0 D, respectively. However, our study did not show results as good as the two reports above. The accuracy of each IOL calculation method seemed to depend on several surgical factors. Most IOL calculation formulas [18,19,20], including the SRK/T formula, assume that the cornea is perfectly spherical and converting corneal radius to diopters is performed using a keratometric refractive index of 1.3375 [3,5,33]. However, most other K-adjusting methods utilize other theoretical indices to correct this keratometric refractive index [33]. Therefore, regression formulas in which adjusted K values are applied may not be suitable models to use with the SRK/T formula. The AL and K values were not considered in our formula, thus relevant corneal power was not considered in IOL power calculations. The application of effective corneal power is quite important in IOL power calculations after refractive surgery. Nevertheless, relatively good predictive outcomes were obtained with our method when only converted ELP values were applied. Our results imply that relevant ELP estimation may be quite important, as much as AL and K, in IOL power calculations for eyes that had previously undergone corneal refractive surgery.