Diurnal variation of corneal and corneal epithelial thickness measured using optical coherence tomography

To determine the feasibility of optical coherence tomography (OCT) measurement of overnight corneal swelling and de-swelling and, specifically, to examine overnight changes in the corneal epithelium and recovery during the day.

Ten healthy volunteers were recruited. Corneal OCT imaging was performed at 10:00 PM (baseline), 8:30 AM, and every 2 hours thereafter until 4:30 PM. Either the right or left eye was taped shut (using a gauze pad and surgical tape) until the 8:30 AM session of the next day. Measurements were made along a 1-mm strip centered on the visual axis.

At baseline, there were no differences in corneal or epithelial thickness between control and experimental eyes (all p > 0.05). Immediately after patch removal, corneal and epithelial thicknesses of patched eyes were higher than the baseline (all p < 0.05). In patched eyes, the cornea and epithelium swelled 5.5% and 8.1% overnight, respectively (p > 0.05). Two hours later, the epithelial thickness of the experimental eyes recovered to baseline level (p > 0.05), but corneal thickness did not reach to baseline level until 4 hours after patch removal. For control eyes, there were no differences compared with baseline (all p > 0.05).

Both cornea and corneal epithelium experience proportionately similar amounts of overnight swelling. Recovery of overnight swelling may be slower for the cornea than for the epithelium. OCT provides valuable information about anterior segment morphometry.