In Vivo Intraocular Lens Thickness Measurement and Power Estimation Using Optical Coherence Tomography

Purpose: To estimate the power of an implanted intraocular lens (IOL) by measuring IOL thickness using anterior segment optical coherence tomography (AS-OCT) and to assess the repeatability of measurements. Methods: Ninety-seven eyes were studied one month after uneventful phacoemulsification within the bag Acrysof SA60AT IOL implantation (range +11 to +35). All eyes had postoperative refraction of +/- 0.5 D of target refraction. AS-OCT was used to measure the central thickness of the IOL. Correlation between labelled IOL power and central IOL thickness as well as the measure of repeatability, for example, intraclass correlation coefficient (ICC), were evaluated. IOL thicknesses were also calculated using a formula and compared with AS-OCT derived measurements. Results: IOL thickness correlated significantly with labelled IOL power (R-2 = 0.985, P < 0.001). The regression equation (IOL Power = [0.04 x IOL thickness in micron] - 7.56) indicates 25 microns of central IOL thickness change per 1D power change. Over the studied range, IOL power could be estimated with a precision of 0.85 +/- 0.02 D (95% confidence interval: 0.83-0.94D). ICC for repeated measurements was 0.999. There was a significant correlation between calculated and measured (AS-OCT) IOL thickness (R-2 = 0.984, P < 0.001). Conclusion: Central IOL thickness measurements with the AS-OCT are highly repeatable and closely correlated with the labelled IOL power, which can predict the IOL power with +/- 0.85 D from the actual power. This method can be helpful in cases of postoperative IOL surprise.