The accuracy of intraocular lens power calculation formulas for eyes longer than 25.00 mm and the correlation between method accuracy and eyeball axial length

Aim of the study
To compare the accuracy of intraocular lens power calculation formulas and examine the correlation of this accuracy with the axial length for eyes larger than 25.00 mm

Material and methods
The data of myopic patients who underwent uneventful phacoemulsification between October 2015 and June 2019 were reviewed. The intraocular lens power for each patient was calculated using 6 formulas (Holladay1, SRK/T, Hoffer Q, Holladay 2, Haigis and Barrett Universal II) before cataract surgery. Postoperative refraction was measured and refractive prediction error was calculated 3 months after phacoemulsification. The correlation between axial length and absolute error was evaluated.

Results
Seventy patients (81 eyeballs with ocular axial length between 25.01 mm and 28.57 mm) were studied. The Barrett Universal II formula achieved the lowest level of mean absolute error of 0.08 ±0.08 D (p < 0.001). Significant correlations for the Holladay 1 (r = 0.478, p < 0.001), the Barrett Universal II (r = 0.312, p = 0.005) and for the Hoffer Q (r = 0.293, p = 0.008) formula were observed.

Conclusions
1. The Barrett Universal II formula obtained the lowest absolute error and is recommended for intraocular lens power calculation for eyeballs with axial length exceeding 25.0 mm. 2. The correlation between axial length and absolute error is a factor which should be considered when calculating intraocular lens power, especially for eyeballs with an extremely large axial length.