Date Published: June 6, 2019
Publisher: Public Library of Science
Author(s): So Jung Ryu, Du Roo Kim, In Seok Song, Yong Un Shin, Mincheol Seong, Heeyoon Cho, Min Ho Kang, I-Jong Wang.
To evaluate the influence of low signal-to-noise ratio (SNR) of axial length measurement, achieved using IOLMaster, on prediction of target refraction.
A total of 131 eyes of 131 patients who underwent phacoemulsification with posterior chamber lens implantation were enrolled. Preoperative axial length measurements were performed with the IOLMaster 500 (Carl Zeiss Meditec, Germany); preoperative SNR values were used to divide the eyes into three groups (Group 1; SNR <10, Group 2; 10 ≤ SNR <50, Group 3; 50 ≤ SNR <100). One month and 6 months after cataract surgery, the manifest refraction spherical equivalents (MRSE) were measured. The mean numeric errors (MNE), the mean of the difference between postoperative MRSE, and preoperative target refraction, using the various intraocular lens (IOL) formulas, were calculated and compared among the three groups. One month after cataract surgery, postoperative MRSE was more hyperopic than preoperative target refraction, calculated by the Haigis formula in group 1, and by the SRK/T formula in group 2. After 6 months, for all formulas in group 1, there were significantly hyperopic results (approximately 0.35 diopter). Upon comparison of MNE among the three groups, group 1 was statistically significantly different from the other groups by Haigis formula. When the SNR values in biometry, using IOLMaster, are <10, careful attention should be given to determining IOL power, as postoperative spherical equivalents are more hyperopic than preoperative target refraction by IOL formula.
The precise measurement of the axial length (AL) and corneal power is important in the calculation of intraocular lens (IOL) power.[1, 2] As commonly known, an inaccurate AL measurement results in crucial errors in postoperative refraction; thus, more accurate measurement of AL has been required to respond the increasing demand for cataract surgery as a refractive correction. Until the 1990s, measurements of AL were generally performed by A-scan ultrasound, which has a low repeatability and can change by pressing the cornea or alternating observers.[4–6] After development of laser interferometry, such as IOLMaster, it has been widely used to decide the IOL power. IOLMaster has been a useful, uncomplicated, non-contact device for calculation of the required IOL power and optimization of the A-constant by measurement of the AL, radius of corneal curvature, and anterior chamber depth.[5, 6, 8–15]
Our study showed postoperative hyperopia in group 1 according to the Haigis formula and in group 2 by the SRK/T formula, at 1 month postoperatively. At 6 months, in group 1, the postoperative MRSE was approximately 0.35 D more hyperopic than the preoperative target refraction, as calculated by all formulas. Group 1 exhibited statistically significant differences using the Haigis formula, compared with groups 2 and 3. We also found a correlation of worse preoperative visual acuity with low SNR.