Dual study on the sum-of-segments method for axial length measurement: is it better?. Issue 1 (January 2023) - Olsen, Thomas
Abstract : The sum-of-segments axial length method was double checked by comparing preoperative and postoperative readings and by evaluating the accuracy of IOL power calculation. Abstract : Purpose: To evaluate the sum-of-segments (SOS) method for optical axial length (AL) measurements. Setting: Department of Ophthalmology, University of Aarhus, Denmark, and Private practice, Copenhagen, Denmark. Design: Retrospective observational study. Methods: 2 retrospective datasets were included. The first dataset comprised 1491 university cataract cases measured with the LENSTAR LS900 preoperatively and 1 to 4 months postoperatively. The second dataset comprised 904 lens surgery cases with refractive follow-up to study the accuracy of intraocular lens power calculation. The prediction accuracy was evaluated as the difference between the observed and the expected refraction. Results: The mean difference between the preoperative and the postoperative AL readings was −0.06 mm and −0.020 mm for the standard and the SOS AL method, respectively, however with a larger variation for the SOS AL method ( P < .01). For the second dataset, the SOS method was found to increase the accuracy of the SRK/T and the Holladay formulas. With the Olsen formula, the SOS method was found to be worse ( P < .01). The highest accuracy was found using standard AL with the Olsen formula, with a mean absolute error of 0.24 diopter (D) and 89.8% of the cases within ±0.5 D. Conclusions: The SOS method improved the accuracy of the classical formulas probably because the optical path is a better representative of the true AL. The Olsen formula already incorporates an optical path correction, and this may be the reason for the lack of improvement with the SOS method.