Purpose: To determine the most accurate method of estimating scleral-spur-to-scleral-spur (STS) distance for ophthalmologists without access to an anterior chamber optical coherence tomography (AS-OCT) instrument when selecting an anterior chamber intraocular lens (AC IOL).
Setting: Robert Cizik Eye Clinic, Houston, TX.
Design: Prospective cohort study.
Methods: The eyes of 65 participants aged 18 years or older were imaged by the Lenstar LS 900 optical biometer and CASIA SS-1000 swept-source Fourier-domain AS-OCT. Eyes were excluded if the anterior segment anatomy was significantly altered and the angle could not be visualized. When both eyes were eligible, 1 eye was randomly selected. The white-to-white (WTW) distance, STS distance, and axial length were recorded and compared. The difference between STS and horizontal WTW was calculated for each meridian. The mean (±SD) differences, 95% limits of agreement, and Bland-Altman agreement were computed for each pair of STS and WTW measurements.
Results: The study comprised 65 eyes of 65 participants. In nearly every case, WTW + 0.5 and WTW + 1 overestimated STS. The horizontal WTW without adjustment was the best predictor of STS. The WTW best corresponded to the vertical STS meridian (6 to 12 o'clock) and not the horizontal meridian (3 to 9 o'clock), along which AC IOLs are traditionally placed.
Conclusions: The horizontal WTW method without an adjustment factor most accurately estimated STS distance and should be used to select AC IOL size when AS-OCT is not available. If AS-OCT is available, it should be used instead. In addition, AC IOLs should be placed in a vertical orientation rather than the traditional horizontal orientation to minimize sizing errors.