Measurement of corneal and limbal epithelial thickness by anterior segment optical coherence tomography and in vivo confocal microscopy

BACKGROUND: To compare corneal epithelial thickness (CET) and limbal epithelial thickness (LET) measured by anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscope (IVCM) in normal subjects, and evaluate the consistency between them. METHODS: Thirty-eight normal subjects (17 men and 21 women) were enrolled in this study. AS-OCT was performed at central cornea and the superior, inferior, nasal and temporal limbus. Then followed by IVCM examination performed at the same location. Agreement was analyzed by mean difference (AS-OCT minus IVCM), 95 % limits of agreement (LoA) (1.96 standard deviation of the difference), and Bland-Altman analysis. RESULTS: The average CET measured by AS-OCT and IVCM was 55.6 ± 4.0 μm and 51.9 ± 4.9 μm respectively. The value measured by IVCM was significantly lower than that measured by AS-OCT (P = 0.015). The average LET values tested by AS-OCT were 10.3 and 10.9 % less at nasal and temporal quadrant (nasal: P = 0.019, temporal: P = 0.003), and were similar as those measured by IVCM at superior and inferior quadrant. In subjects older than 40 years, CET and LET values measured by AS-OCT were significantly higher than those by IVCM. Such differences were not found in subjects ≤ 40 years old. CONCLUSIONS: CET values measured by IVCM are lower than those by AS-OCT, while LET values measured by two devices have good agreement. These two techniques have their own advantages in measuring epithelial thickness and are mutually complementary.