Impaired subjective morning visual acuity with improvement of symptoms during the day is pathognomonic for corneal endothelial dysfunction in advanced Fuchs endothelial corneal dystrophy (FECD). This study aimed to analyze the daily fluctuations of corneal thickness, refraction, and (glare) visual acuity in advanced FECD.Prospective cohort study.Patients with advanced FECD (FECD group) and patients with normal cornea (control group) were enrolled. Routine clinical examination was performed using slitlamp biomicroscopy, funduscopy, macular OCT. In addition, assessment using corneal Scheimpflug tomography (Pentacam), refraction, corrected distance visual acuity (CDVA) and glare CDVA was performed at 4pm (afternoon) and the following day at 8am (morning).A total of 29 FECD eyes and 22 control eyes were included. Diurnal variations from afternoon to morning were Δcorneal thickness (apex) ± standard deviation (SD) 41.45±34.1μm (p<0.001, FECD group) and 5.5±6.72μm (p=0.001, control group); Δspherical equivalent ± SD -0.64±0.6 dpt (p<0.001, FECD group) and -0.01±0.50 dpt (p=0.461, control group); Δtotal corneal refractive power (TCRP) ± SD 0.60±0.83 dpt (p=0.001, FECD group) and -0.01±0.49 dpt (p=0.602, control group), Δ corrected distance visual acuity (CDVA) ± SD 0.15±0.18 LogMAR (p<0.001, FECD group) and 0.02±0.04 LogMAR (p=0.174, control group), Δ CDVA glare ± SD 0.34±0.25 LogMAR (p<0.001, FECD group) and 0.05±0.11 LogMAR (p=0.106, control group).A morning myopic shift and increased glare paralleling increased corneal thickness may particularly contribute to subjective visual impairment in advanced FECD in the first hours after awaking. This should be taken into account during assessment and surgical decision-making in FECD patients.