title: Comparison of the precision of the Topcon SP-3000P specular microscope and an ultrasound pachymeter.
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Turki M
authors.initials: TM
authors.lastname: Almubrad
authors.forename: Uchechukwu L
authors.initials: UL
authors.lastname: Osuagwu
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Alabbadi
authors.forename: Kelechi C
authors.initials: KC
authors.lastname: Ogbuehi