Differences in corneal thickness and corneal epithelial thickness measured by two kinds of frequency domain anterior segment OCT and the consistency between them

Objective

To investigate the differences in corneal thickness and corneal epithelial thickness measurements by two kinds of high-resolution frequency domain anterior segment optical coherence tomography (OCT), RTVue XR-OCT and Cirrus 5000 HD-OCT, and to analyze the consistency between them.

Methods

A cross-sectional study was conducted.Fifty-two patients (52 eyes) who were admitted to Henan Eye Hospital from July to September 2019 were enrolled.The corneal thickness and corneal epithelial thickness in various areas including the central area (C area) (2-mm diameter), and 8 concentric corneal areas of 2 to 5-mm diameter, which were the superior area (S area), the superior nasal (SN area), the nasal side area (N area), the inferior nasal area (IN area), the inferior area (I area), the inferior temporal area (IT area), the temporal area (T area) and the superior temporal area (ST area) above the temporal, were measured by the same examiner using RTVue XR-OCT and Cirrus 5000 HD-OCT.The corneal thickness and corneal epithelial thickness measurements were compared to analyze the difference, correlation and consistency between the two kinds of OCT.This study adhered to the Declaration of Helsinki.The study protocol was approved by an Ethics Committee of Henan Eye Hospital (No.HNEECKY-2021[06]). Written informed consent was obtained from each subject prior to any medical examination.

Results

The corneal thickness measured by RTVue XR-OCT in C, S, SN, N, IN, I, IT, T, ST areas were (521.73±29.85), (554.31±32.38), (553.54±33.30), (546.96±32.05), (537.54±32.10), (532.13±31.51), (528.42±30.38), (532.25±30.08), (544.85±30.70)μm, respectively, and the corneal thickness in the 9 areas measured by Cirrus 5000 HD-OCT were (526.77±30.62), (555.13±33.32), (558.08±32.57), (554.46±31.42), (548.29±31.84), (539.69±32.74), (536.19±32.40), (533.38±31.90), (543.83±32.02)μm, respectively.There was no significant difference in corneal thickness of various areas between the two kinds of OCT (all at P>0.05), and there were positive correlations between them (r=0.99, 0.89, 0.95, 0.97, 0.95, 0.93, 0.96, 0.97, 0.92; all at P<0.01). Bland-Altman analysis showed that there was a good consistency of corneal thickness measurements by the two kinds of OCT.The corneal epithelial thickness in C, S, SN, N, IN, I, IT, T, ST areas measured by RTVue XR-OCT were (52.06±3.26), (52.58±3.48), (53.06±3.56), (53.75±3.49), (53.81±3.40), (53.48±3.35), (52.96±3.32), (52.67±3.19), (53.12±3.15) μm, respectively, and the corneal epithelial thickness in the 9 areas measured by Cirrus 5000 HD-OCT were (46.75±3.25), (47.40±3.36), (47.58±3.64), (48.85±4.48), (48.46±4.54), (48.40±4.96), (48.06±5.12), (47.46±3.91), (48.79±3.90)μm, respectively.There were statistically significant differences in the corneal epithelial thickness of various areas measured by the two kinds of OCT (all at P<0.05), and there was no significant correlation between them (r=0.17, 0.08, 0.16, 0.28, 0.20, 0.24, 0.19, 0.21, 0.13; all at P>0.05). Bland-Altman analysis showed poor consistency of corneal epithelial thickness measurements between the two kinds of OCT.

Conclusions

There is no significant difference in measuring corneal thickness between the two kinds of OCT and the consistency is high, which means that they can be replaced by each other.There are significant differences in corneal epithelial thickness measurement between them and the consistency is poor, so they are not interchangeable.

Cornea; Epithelium, corneal; Thickness; Anterior eye segment; Tomography, optical coherence; Difference; Consistency