Estimation of the thickness of the crystalline lens from on-axis and off-axis Scheimpflug photographs.

Measurement of human lens biometry directly from Scheimpflug images of the anterior ocular segment may be impossible when pupil size precludes an adequate Scheimpflug view of the posterior lens surface. The authors describe a simple and accurate geometric method of overcoming this problem by estimating the true lens thickness from pairs of on-axis and off-axis Scheimpflug images. The method is validated and the variability of the estimate is quantified. This new method has utility in the study of lens biometry in subjects with large lenses whose pupils cannot be adequately dilated.