This study examined intraobserver and interobserver reproducibility of corneal thickness (CT) and epithelial thickness (ET) measurement of Fourier domain OCT (RTVue) in 23 healthy volunteers. RTVue is capable of producing 26,000 A scans per second with depth resolution of 5µm. All patients underwent three sessions of examinations, totalling nine CT and ET measurements each. Sessions were taking place at different times during a day (9am and 4pm) and 9am the next day. CT and ET were evaluated at nine different corneal locations. The intraobserver and interobserver reproducibility was almost perfect for both CT and ET at most measured locations and substantial for six and 12 o’clock locations. Interestingly data showed significant difference in CT and ET between morning and afternoon measurements. CT and ET were significantly thinner in the afternoon by -3.15µm and -0.52µm respectively. This might be secondary to overnight swelling and daily detumescence of the cornea secondary to reduced oxygen level and evaporation of tear film beneath the closed eyelids. This may represent physiological changes in CT and ET, but values are below the manufactures depth resolution, therefore need to be looked at with caution.

Reproducibility and daytime-dependent changes of corneal epithelial thickness and whole corneal thickness measured with Fourier domain optical coherence tomography.
Wasielicka-Poslednik J, Lisch W, Bell K, et al.
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Magdalena Popiela

Royal Gwent Hospital, Cardiff, UK.

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