Fritz M, Grewing V, Maier P, et al. - Since the extent of diurnal variation in corneal edema in Fuchs dystrophy is not known, researchers conducted this prospective cohort study to measure corneal thickness and posterior profile over the course of the day utilizing Scheimpflug imaging. Candidates with clinically advanced Fuchs dystrophy eyes undergoing endothelial keratoplasty and candidates with healthy corneas were evaluated around noon the day before surgery and late afternoon, in presumed steady state. Candidates were evaluated immediately upon eye-opening in the hospital the morning of surgery after controlled overnight patching to standardize eyelid closure. Patients had mean corneal thickness of 663 μm in Fuchs dystrophy and controls had thickness of 557 μm directly upon awakening. Over time, there were no systematic changes in the control corneas. Corneal thickness reduced after awakening in Fuchs dystrophy eyes. For clinically advanced Fuchs dystrophy, impaired hydration control makes measurements of key corneal parameters inaccurate immediately after eye-opening. Corneal thickness measurements are unlikely to vary more in Fuchs dystrophy eyes than in normal eyes beyond the first hours after eye-opening.