Comparison of the precision of the Topcon SP-3000P specular microscope and an ultrasound pachymeter

Turki M Almubrad, Uchechukwu L Osuagwu, Ibrahim AlAbbadi, Kelechi C Ogbuehi
Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia

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 µm (range 417.33–592.67) and 516.94 ± 33.60 µm (range 431.67–582.67) for sessions 1 and 2 respectively, with the NCSM; 546.69 ± 36.62 µm (range 457.33–617.00) and 549.78 ± 35.26 µm (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 µm (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 µm vs ± 12 µm in session 1 and ±8 µm vs ±10 µm in session 2). The reproducibility coefficient with the NCSM was half that with the USP (±21 µm vs ±41 µm).
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.

Keywords: cornea, Topcon SP-3000P, ultrasound pachymetry, repeatability coefficient, reproducibility coefficient