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Purpose:The goal of this study was to investigate diurnal changes in intraocular straylight in relation to other corneal parameters and subjective complaints in patients with Fuchs endothelial dystrophy and healthy controls.Methods: This is a prospective study conducted in 2 tertiary care hospitals in Germany and the Netherlands. Patients with Fuchs endothelial dystrophy (n = 71) and healthy controls (n = 34) were included. Patients with Fuchs dystrophy were grouped by the presence of subjective complaints and measured over multiple time points during the day. Measurements included intraocular straylight using the C-Quant and corneal thickness and backscatter using a Scheimpflug camera. A separate group of healthy controls was measured intensively with repeated straylight measurements directly after waking. An exponential decay model was used to model the diurnal change.Results: Healthy controls showed an average straylight baseline of 1.17 log(s) with an increase in straylight after waking of 0.22 log(s). In the repeated measurements subgroup, the increase in morning straylight lasted for 22 minutes. Patients with Fuchs dystrophy showed a morning increase in straylight of 0.21 log(s) present up to 4 hours after waking before reaching an average baseline of 1.30 log(s). Straylight was positively correlated with anterior corneal backscatter, r = 0.21, P = 0.022, and corneal thickness, r = 0.46, P , 0.01. Conclusions:Healthy eyes experience a diurnal straylight increase similar to patients with Fuchs dystrophy in intensity. However, in Fuchs dystrophy, the resolution of increased straylight is prolonged over multiple hours compared with minutes in healthy eyes. This suggests pathological exacerbation of a physiological diurnal change. This mechanism can play a role in subjective complaints experienced by patients with Fuchs dystrophy.

Purpose:Patients with advanced Fuchs endothelial corneal dystrophy frequently report poor vision in the morning, which improves as the day progresses. This study quantified the amount of variation in near and distance visual acuity and refraction over the course of a day.Methods:This was a prospective cohort study. Best-corrected distance visual acuity and near visual acuity were tested in participants with clinically advanced Fuchs dystrophy and in controls with healthy corneas. Subjective refraction and autorefraction were conducted in a presumed steady state in the afternoon. Measurements were repeated directly after eye opening in the hospital the next morning. In a subgroup, measurements were repeated every 30 minutes for up to 2 hours.Results:In Fuchs dystrophy, the mean distance visual acuity was worse by −3 letters (95% confidence interval, −4 to −1) directly after eye opening in the morning compared with late afternoon. No such difference was seen in healthy corneas. In Fuchs dystrophy, visual acuity improved over the course of the study. Visual acuity in the morning could be improved with fine tuning of refraction, and refractive changes were exclusive to Fuchs dystrophy (0.5–1.0 D in spherical equivalent in 30%, >1.0 D in 2% of eyes).Conclusions:Distance and near visual acuity and refraction changes over the course of the day in patients with advanced Fuchs dystrophy. Although small changes in refraction may not usually require a second set of glasses for the first hours of the day, diurnal variation should be considered when determining disease severity in routine practice and in clinical trials.