The aim of this study was to evaluate the prediction accuracy of modified Wang-Koch SRK/T formula in high myopia eye with different axial lengths (AL) after cataract surgery.

The study comprised 63 eyes of 59 cataract patients with high myopia in Chengdu AIER EYE Hospital between January 2019 to December 2019. Among of them, there were 30 males (33 eyes), 29 females (30 eyes). They were aged 44 to 73 years-old with the mean age of (59.6±8.8) years-old. IOL Master 700 was used to measure the keratometry, AL, anterior chamber depth and lens thickness. An intraocular lens (IOL) with appropriate residual refractive power was individually selected for each eye, and the postoperative residual refractive powers of the SRK/T, Wang-Koch modified SRK/T and Barrett Universal Ⅱ formulas were obtained. According to ALs, patients were dived into three groups: patients with 27.00≤AL<28.00 mm (group A); 28.00≤AL <30.00 mm (group B); and AL≥30.00 mm (group C). The refractive powers of the patients at 1 month after surgery were measured. Then the difference between the preoperative residual refractive power and postoperative refractive power, which was named the mean refractive error, the absolute value of the difference, which was named the mean absolute refractive error (MAE), were calculated. The prediction accuracy was compared between 3 formulas in different groups. Data distribution for normality of the refractive errors was checked using the Shapiro-Wilk test. The quantitative data of normal distributions were expressed by the mean±standard deviation, and the measurement data were tested by analysis of variance. The quantitative data of non-normal distributions were expressed by the median and percentile, and the measurement data were tested by non-parametric tests. The description of the ratio of eyes within different prediction errors were expressed as the number of eyes and percentages, which were compared by chi-square test. Spearman′s rank and line regression was used to test the correlation between AL and MAE.

The MAE of the SRK/T, Wang-Koch SRK/T formula and Barrett Universal Ⅱ formulas were 0.57(0.32, 0.98) D, 0.32(0.17, 0.61) D and 0.34(0.17, 0.66) D, respectively. The MAE in the modified Wang-Koch SRK/T and Barrett Universal Ⅱ formulas were significantly lower than the SRK/T formula. After the analysis of variance, there was significant difference between them (Z=-3.77, -4.28; P<0.05). For the percentage of eyes within ±0.50 D and ±1.00 D of the prediction error, the modified Wang-Koch SRK/T formula had the highest value, which was 69.8% and 98.4%, respectively. No significant difference was found when compared the MAE between three formulas in group A and group B (Z=-0.28, -0.97; P>0.05). In group C, the MAE was significantly higher in the SRK/T formula than in the modified Wang-Koch SRK/T and Barrett Universal Ⅱ formulas. After the analysis of variance, there was significant difference between them(Z=-3.22, -3.29; P<0.05). When using SRK/T formula, MAE and AL had correlation. After correlation analysis, there was significant difference between them (r=0.521, P<0.05). When using Wang-Koch SRK/T formula and Barrett Universal Ⅱ formulas , MAE and AL had no correlation. After correlation analysis, there was non-significant difference between them (r=0.249, 0.228; P>0.05). The regression equation with one unknown of MAE and AL was Y=-3.606+ 0.146X. After Spearman analysis, there was non-significant difference between them (r=0.249, P>0.05).

Intraocular lens power alculation in eyes with high myopia were accurate in all 3 formulas. In patients with AL of 30.00 mm or more, the modified Wang-Koch SRK/T and Wang-Koch SRK/T and Barrett Universal Ⅱ formulas were better than the SRK/T formula.