Dual study on the sum-of-segments method for axial length measurement: is it better?

To evaluate the sum-of-segments (SOS) method for optical axial length (AL) measurements.

Department of Ophthalmology, University of Aarhus, Denmark, and Private practice, Copenhagen, Denmark.

Retrospective observational study.

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.

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.

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.