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Comparison of Central Corneal Thickness using Anterior Segment Optical Coherence Tomography vs Ultrasound Pachymetry
PurposeTo determine if there is a systematic difference in central corneal thickness (CCT) measured using anterior segment optical coherence tomography (AS-OCT) as compared with ultrasound pachymetry.DesignProspective observational study.MethodsConsecutive subjects with clinically normal corneas underwent CCT measurement by both ultrasound and AS-OCT while participating in a population-based study in Ghana, West Africa. One eye of each subject was randomly selected for analysis. Two measurements were taken and averaged. Agreement and interobserver variability were also analyzed.ResultsOne hundred and fifty-five subjects of African ethnicity and average age 57 years (standard deviation [SD] 12; range, 40 to 98 years) were included. Measurements by AS-OCT and US were taken a mean of 15 days (maximum, six weeks) apart. The mean (SD) [range] US CCT was 525.3 μm (33.5) [422, 653] and 499.0 μm (32.0) [428, 613] with AS-OCT. Measurements by the two modalities were strongly correlated (r2 = 0.82; P < .001), and a significant difference was observed between mean US and AS-OCT CCT (SD) [range] of 26.3 μm (14.2) [−63, 12] (P < .001). The width of the limits of agreement was 28 μm, about 6% of the average pachymetry reading. In 50 eyes randomly remeasured with OCT by a second observer, the intraclass correlation coefficient was 0.91. There was a small but significant systematic difference between observers (mean 6.9 μm, SD 10.9 μm), or 1.4% (P < .001), increasing the difference noted above.ConclusionThere is a reproducible systematic difference between CCT measurements taken with ultrasound and OCT. It is important to note in clinical practice, that measurements acquired by these two modalities are not directly interchangeable.