Purpose: The extent of diurnal variation in corneal edema in Fuchs dystrophy is unknown. We measured corneal thickness and posterior profile over the course of the day using Scheimpflug imaging.
Design: Prospective cohort study.
Methods: Participants with clinically advanced Fuchs dystrophy eyes undergoing endothelial keratoplasty and participants with healthy corneas were assessed around noon the day before surgery and late afternoon, in presumed steady state. After controlled overnight patching to standardize eyelid closure, participants were assessed immediately upon eye opening in hospital the morning of surgery.
Results: Directly upon awakening, patients had mean corneal thickness of 663 μm (interquartile range [IQR], 625-707) in Fuchs dystrophy (n = 44) and controls (n = 11) had thickness of 557 μm (IQR, 527-601). In control corneas, there were no systematic changes with time. In Fuchs dystrophy eyes, corneal thickness decreased after awakening. Ninety-five percent of patients can be expected to have a decrease in corneal thickness over the first 4 hours after awakening between 31 μm and 58 μm (95% prediction interval). Posterior Q decreased on average by 0.15 (95% confidence interval [CI], 0.07-0.23) and posterior radius of curvature decreased by 0.20 mm (95% CI, 0.14-0.27) over the first 4 hours, indicating that edema resolution steepened the central posterior cornea. Beyond 4 hours after awakening, corneas no longer changed considerably in Fuchs dystrophy.
Conclusion: Impaired hydration control in clinically advanced Fuchs dystrophy makes measurements of key corneal parameters unreliable directly after eye opening. Beyond the first hours after eye opening, corneal thickness measurements are unlikely to vary more in Fuchs dystrophy eyes than in normal eyes.
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