Is the cornea thickest in the morning or at night?

The cornea is indeed thickest in the morning. This phenomenon is primarily due to diurnal variations in the hydration of the corneal stroma. During sleep, the eye's normal function, including tear exchange, is reduced, leading to an accumulation of fluids in the corneal tissue. As a result, the cornea can swell due to increased hydration, reaching its maximum thickness in the early morning hours.

After awakening, the cornea generally returns to its typical thickness throughout the day as the tear film stabilizes and normal metabolic processes resume, allowing for a decrease in stroma hydration. Thus, the timing of these changes aligns with the understanding that the eye's corneal thickness peaks during the night and is most pronounced in the morning upon waking.