Comparison of Central Corneal Thickness Measurements Using Ultrasound Pachymetry and Anterior Segment Optical Coherence Tomography

Background: Central corneal thickness (CCT) is a cornerstone parameter in ophthalmology. It influences glaucoma risk assessment, refractive surgery safety margins, and corneal health evaluation. Traditionally, ultrasound pachymetry (USP) has been regarded as the gold standard, but its reliance on corneal contact and topical anesthesia limits its utilisation. Anterior segment optical coherence tomography (AS-OCT), a non-contact imaging modality, offers a high-resolution alternative. This study aimed to compare CCT measurements obtained by USP and AS-OCT in healthy adults, assessing their agreement and clinical interchangeability. Methodology: A cross-sectional study was conducted in 70 healthy adults aged 18–60 years. Each participant underwent CCT measurement by AS-OCT followed by USP, with the average three readings each per eye. To minimize the effect of diurnal variation, all measurements were performed between 10 am and 2 pm. Statistical analyses included paired-sample t-tests, Bland–Altman plots, Pearson correlation, and intraclass correlation coefficients (ICC). Results: USP consistently yielded higher values (mean 550.7 ± 36.2 μm) compared with AS-OCT (mean 528.5 ± 37.4 μm). The mean difference of 22.1 μm was statistically significant (p < 0.001), with 95% confidence intervals ranging from 17.4 to 26.9 μm. Despite this systematic bias, a strong positive correlation was observed (r = 0.856, p < 0.001), and USP demonstrated high reliability (ICC = 0.92). Bland–Altman analysis confirmed systematic differences, with limits of agreement spanning –16.5 to +60.7 μm. Conclusion: USP and AS-OCT provide strongly correlated but systematically different CCT measurements. USP consistently yields higher values, therefore, the two methods should not be used interchangeably. For accurate longitudinal monitoring, clinicians should employ the same device consistently. AS-OCT offers a practical non-contact alternative, but interpretation requires device-specific normative data. Recognizing these discrepancies is essential for precise glaucom