[Accuracy of Optical Coherence Tomography versus Ultrasound in pachymetry]

Measuring the central corneal thickness is an important step in the diagnosis and monitoring of glaucoma. Ultrasound pachymetry was the gold standard before the advent of OCT. The purpose of this study is to assess the reliability of OCT pachymetry compared to ultrasound pachymetry in black patients.

Pachymetry was performed as part of a glaucoma work-up. Ultrasonic pachymetry was measured using the Alcon Ocuscan by the same operator and OCT pachymetry using the Topcon 2000 OCT. The Student's t-test was used to compare means with statistical significance of 5%. The Pearson's correlation coefficient (r²) was used to measure correlations.

One-hundred thirty-five right eyes and 135 left eyes, corresponding to 270 eyes of 135 patients, were examined. There was a female predominance (59 men/76 women), with a gender ratio of 0.78. The mean age was 42.3±17.3 [8-86] years. In the right eye, the mean OCT pachymetry was 522.4±36.8μ versus 528.2±37.9μ for ultrasonic pachymetry (P=1.00). In the left eye, the mean OCT pachymetry was 522.0±33.8μ versus 524.9±42.5μ for ultrasonic pachymetry (P=1.00). The overall mean OCT pachymetry was 522.2±35.2μ versus 526.5±40.2μ, with a non-significant difference (P=1.00). There was a strong correlation between ultrasonic pachymetry and OCT pachymetry (r²=0.83; P<0.05). On the other hand, there was a very low correlation between pachymetry and age (r²=0.09; P<0.05). Pachymetry decreased by 5μ per 10 years, corresponding to corneal thinning of 0.5μ per year.

OCT pachymetry can be a reliable alternative to ultrasound pachymetry and could be performed at the same time as the OCT for glaucoma assessment.