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Comparison of Orbscan and Ultrasound Pachymetry Measurements

Comparison of Orbscan and Ultrasound Pachymetry Measurements. Faik Orucov, MD , Abraham Solomon, MD, Ziv Caspi , David Landau, MD, Eyal Strassman, MD, Joseph Frucht-Pery, MD. Department of Ophthalmology, Hadassah University Hospital; School of Medicine – Hebrew University, Jerusalem, Israel.

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Comparison of Orbscan and Ultrasound Pachymetry Measurements

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  1. Comparison of Orbscan and Ultrasound Pachymetry Measurements Faik Orucov, MD, Abraham Solomon, MD, Ziv Caspi, David Landau, MD, Eyal Strassman, MD, Joseph Frucht-Pery, MD Department of Ophthalmology, Hadassah University Hospital; School of Medicine – Hebrew University, Jerusalem, Israel

  2. Purpose To compare central corneal thickness measurements (CCT) using Orbscan II (Bausch and Lomb, Rochester, NY) and Sonogage ultrasonic (US) pachymetry in normal eyes of large population. Authors have no financial interests in any of the mentioned products or companies

  3. Methods • January 2002 and January 2006 (All LASIK patients) • Hadassah University Hospital • Missing records of any variables were excluded from the study. • Thinnest point included for Orbscan II and for US pachymetry after at least 3 repeated measurements. • The Student t test

  4. Rersults • 6466 eyes were included in the study. • Acoustic correction factor of 0.96 • Orbscan II measurements were significantly higher than US pachymetry measurements (553.8 ± 41.2 micron and 531.7± 31.6 micron, respectively) (P < 0.0001). • Corneal thickness measured by US pachymetry was approximately 22.1± 19.7 microm (4%) smaller than the thickness measured by Orbscan II with correction. • A significant correlation was observed between ultrasound pachymetry and Orbscan slitscan pachymetry (Pearson correlation coefficient, r = 0.887; P < 0.001).

  5. Difference US Orbscan P Positive 538.2 575.4 0.0001 Minimal 525.3 533.2 0.0001 Negative 514.1 477.9 0.0001 The differences between orbscan and US pachymetry are divided to three as, • High Positive Difference when orbscan measured thicker than 22 micron and • High Negative Difference when orbscan measured thinner than 22 micron and • Small Difference when measurements were ± 22 micron. • High positive differences appeared in thicker corneas • High negative differences appeared in thin corneas US Pachymetry Orbscan pachymetry • The cylinder was higher in negative differences than the positive differences (Mean -1.26±1.4 diopter and -0.87±0.9 diopter; P<0.001) while simK’s were same between groups ( P=0.491 and P=0.585 ).

  6. Conclusion • Orbscan scanning-slit system obtained significantly different values for corneal thickness. (acoustic correction factor of 0.96) • The differences between two devices are more in thick and thin corneas. • The degree of variability within each group indicated that these two techniques are not clinically comparable. • These differences are important for planning and measuring the effects of corneal refractive procedures.

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