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Corneal thickness, curvature, and elevation readings in normal corneas: Combined Placido–Scheimpflug system versus combined Placido–scanning-slit system

Journal of Cataract & Refractive Surgery
DOI: 10.1016/j.jcrs.2012.01.033
  • Medicine


Purpose To evaluate agreement in central corneal thickness (CCT), keratometry, and anterior and posterior elevation map measurements in normal corneas between a combined Placido–Scheimpflug system and a combined Placido–scanning-slit elevation topography system. Setting Department of Cataract & Refractive Surgery, Rothschild Foundation, Paris, France. Design Evaluation of diagnostic test or technology. Methods Measurements were performed with a combined Placido–Scheimpflug system (TMS-5) and a combined Placido–scanning-slit system (Orbscan II). Ultrasound (US) pachymetry was used as the reference for CCT measurements. Bland-Altman plots were used to evaluate agreement between instruments. Results The mean CCT measurements by US pachymetry, the Placido–Scheimpflug system, and the Placido–scanning-slit system were 556.74 μm ± 42.45 (SD), 543.23 ± 36.73 μm, and 564.45 ± 41.26 μm, respectively. Although the CCT readings were statistically significantly thinner with the Placido–Scheimpflug system than with the other systems, there was high correlation between instruments. Peripheral corneal thickness readings were also thinner with the Placido–Scheimpflug system than with the Placido–scanning-slit system. Keratometry and anterior and posterior best-fit sphere (BFS) measurements were comparable between the 2 optical devices. Anterior and posterior maximum central elevations measured by the 2 instruments were not comparable or strongly correlated. Repeatability after 3 successive measurements was excellent for all parameters except maximum central elevation. Conclusions Although highly correlated, with corneal thickness readings were not interchangeable between the 2 optical devices. No statistically significant differences in keratometry or BFS measurements were observed between the 2 devices. There were important discrepancies in the maximum central elevation between the 2 topographers. Financial Disclosure Drs. Gatinel and Saad are consultants to Technolas Perfect Vision. No other author has a financial or proprietary interest in any material or method mentioned.

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