The Comparative Study of Refractive Index Variations between Haigis, Srk/T and Hoffer-Q Formulas Used for Preoperative Biometry Calculation in Patients with the Axial Length >25 mm.

BACKGROUND: To compare refractive index variation between Hoffer-Q, Haigis and SRK/T formulas used for preoperative biometry calculation in patients with axial length >25 mm, undergoing cataract surgery.

MATERIALS AND METHODS: This is a randomized clinical trial study was performed on 54 eyes of 54 patients with ages of 40-70 years old and axial length >25 mm classified into three groups that their IOL POWER were calculated by Haigis, SRK/T and Hoffer-Q formulas before undergoing cataract surgery. Their refractive index variations were calculated from the difference between predicted refractive error formula and actual post-operative refractive error formula. The collected data was entered in SPSS software and was analyzed by ANOVA and Chi-square statistical test.

RESULTS: With comparison sphere, astigmatism and spherical equivalent indexes before and after of cataract surgery between Haigis, SRK/T, and Hoffer-Q formulas, statistically significant differences were found between the mean of sphere and SE indexes in patients with use of Haigis and SRK/T formulas that have been more favorable post-operative refraction.

CONCLUSIONS: Haigis formula and then, with slight difference, SRK/T formula have better and more acceptable post-operative refraction results than Hoffer-Q formula in patients with high axial myopia. Therefore, it is recommended using Haigis and SRK/T formulas for IOL power calculation in patients with high axial myopia undergoing cataract surgery.