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H. Kim, D. L. Budnez, K. Barton, P. S. Lee, W. Feuer; A Comparison of Central Corneal Thickness (CCT) Using Ultrasound vs. Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3534.
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© ARVO (1962-2015); The Authors (2016-present)
To determine if a systematic difference can be detected when central corneal thickness (CCT) is measured using ultrasound (USS) versus optical coherence tomography (OCT).
The Tema Eye Survey is a population-based study of 5,500 residents of 5 communities in the city of Tema, Ghana, West Africa. 155 subjects enrolled in the Tema Eye Survey, were measured by USS with the Pachmate DGH 55 (DGH, Exton, PA. USA) and OCT using the Heidelberg SL-OCT (Heidelberg Engineering, Heidelberg, Germany). One eye of each subject was randomly selected for analysis. For each eye and each instrument, two measurements were taken and averaged. The data were analyzed using the paired t test and Pearson’s correlation coefficient. A Bland-Altman plot was also constructed to evaluate the agreement between the two instruments.
All subjects were of West African ethnicity. The average age at enrollment was 57 (SD 12, range 40-98) years old. Measurements by OCT and USS were made an average of 15 days apart and a maximum of 6 weeks apart. Results were similar when analysis was performed on the 47 eyes measured with both instruments on the same day. The mean (SD) [range] CCT measured with the Pachmate DGH 55 was 525.3 µm (33.5) [422, 653] and 499.0 µm (32.0) [428-613] with the SL-OCT. The mean Pachmate DGH 55 - SL-OCT difference (SD) [range] was 26.3µm (14.2) [-63, 12](p<0.001). The measurements of the two devices were highly correlated (r2=0.82, p<0.001). A Bland-Altman graph indicated that the magnitude of the difference between the two instruments was not correlated with the average pachymetry measurement. Twice the standard deviation of the difference was 28 µm, about 6% of the average pachymetry reading.
There is a systematic difference of approximately 26.3µm between OCT and USS pachymetry. After accounting for this difference, a variability of ± 28µm can be expected, which is about 6% of the average pachymetry measurement.
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