Limitations of Scheimpflug photography in quantifying glistenings

Behndig and Mönestam1 have described Scheimpflug photography for quantifying glistenings in intraocular lenses (IOLs). We believe the technique is unsuitable for this purpose. The authors measured the intensity of scattered light through the IOL. There is no demonstration of the ability to distinguish between light scatter due to glistenings and light scatter due to other more likely variables, such as the aqueous–IOL interface or biological materials on the IOL surface.2 The observed scatter is primarily at the IOL surfaces, whereas glistenings are more prevalent within the IOL. Glistenings are small (3 to 10 μm),3,4 irregularly distributed microvacuoles within the IOL. As they are irregularly placed, it is not evident how the microvacuoles would generate the systematic intensity distributions depicted in the graphs. We believe analysis of glistenings requires a more discrete analytical approach. The reported correlation coefficients for the given intensity profiles (interpreted as glistenings) and postoperative time were higher for Scheimpflug photography than for subjective grading. Rather than indicating that Scheimpflug imaging is reliable, as the authors conclude, it more likely indicates that the imaging is unrelated to glistenings and perhaps more related to posterior capsule opacification or debris on an IOL, both likely to increase over time. Scheimpflug photography's off-axis illumination can produce significant light scattering even in a clear cornea. This is evident in a cross-sectional photo from Rosales et al.5 in which scatter from a young cornea is higher than from the model eye cornea and lens or a human crystalline lens. Scatter from the Scheimpflug image should not be interpreted as clinically consequential. The limited resolution of the light-scatter intensity, a bias toward IOL borders, and a lack of correlation with clinical observation suggest Scheimpflug imaging is not suitable for characterization of IOL glistenings.