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


METHODS
Department of Cataract & Refractive Surgery, Rothschild Foundation, Paris, France.


METHODS
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.


BACKGROUND
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.
Department of Cataract & Refractive Surgery, Rothschild Foundation, Paris, France.
Emmanuel
E
Guilbert
Alain
A
Saad
Alice
A
Grise-Dulac
Damien
D
Gatinel
D000328:Adult; D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D011446:Prospective Studies; D015203:Reproducibility of Results; D055815:Young Adult