Abstract
Aim: To compare the precision of the Topcon SP-3000P noncontact specular microscope (NCSM) and the DGH 500 ultrasound pachymeter (USP).
Methods: Triplicate measurements of central corneal thickness (CCT) for 100 eyes were taken with an NCSM and a USP in 2 visits separated by 1 week. Repeatability was assessed by computing the differences between all 3 readings from each subject. Coefficients of repeatability and reproducibility were computed.
Results: Mean CCT as measured by each instrument were: 518.53 +/- 34.96 ae m (range 417.33-592.67) and 516.94 +/- 33.60 mu m (range 431.67-582.67) for sessions 1 and 2 respectively, with the NCSM; 546.69 +/- 36.62 mu m (range 457.33-617.00) and 549.78 +/- 35.26 mu m (range 454.00-618.67) for sessions 1 and 2 respectively, with the USP. The ultrasound CCT measurements were consistently higher than those obtained with the NCSM in both sessions 28.17 +/- 19.20 mu m (mean +/- SD, session 1) and 32.81 +/- 14.04 (mean +/- SD, session 2). The repeatability coefficient for the NCSM was better in both sessions than those for USP (+/- 10 mu m vs +/- 12 mu m in session 1 and +/- 8 mu m vs +/- 10 mu m in session 2). The reproducibility coefficient with the NCSM was half that with the USP (+/- 21 mu m vs +/- 41 mu m).
Conclusion: The SP-3000P NCSM is a more precise and reproducible instrument for measurement of CCT than the USP, but both instruments are reliable, useful instruments for measuring CCT.