Purpose
To investigate the validity of Placido‐based corneal topography parameters to predict corneoscleral sagittal heights measured by Fourier‐based profilometry at various diameters.
Methods
Minimal (Minsag), maximal (Maxsag) sagittal height, toricity (Maxsag − Minsag) and axis of the flattest meridian (Minsag) of 36 subjects (mean age 25.4 SD ± 3.2 years; 21 female) were measured using the Eye Surface Profiler and analysed for diameters (chord length) of 8 to 16 mm (in 2‐mm intervals). Furthermore, corneal central radii, corneal astigmatism, eccentricity and diameter were measured using the Keratograph 5 M.
Results
Using multiple linear regression analysis, the best equation for predicting the sagittal heights for 8 mm (r2 = 0.95), and 10 mm (r2 = 0.93) diameters included corneal central radii and eccentricity. The best equation for predicting sagittal heights for 12 mm (r2 = 0.86), 14 mm (r2 = 0.78) and 16 mm (r2 = 0.65) diameters included corneal central radii, eccentricity and corneal diameter. Corneal astigmatism was significantly correlated with sagittal height toricity for 8 and 10 mm diameters (r2 = 0.50 and 0.29; p < 0.01), while no correlation was observed for 12, 14 and 16 mm diameters (p = 0.18 to p = 0.76). The axis of the flattest corneal meridian measured by Placido‐based topography was significantly correlated with the axis of the flattest meridian measured by Fourier‐based profilometry for 8, 10 and 12 mm diameters (r2 = 0.17 to 0.44; p < 0.05), while there was no correlation for 14 and 16 mm diameters (p = 0.48 and p = 0.75). For a typical soft contact lens diameter of 14 mm, 78% of the variance could be determined with a corneal topographer and 68% with keratometry and corneal diameter measurement.
Conclusions
The combination of corneal central radii, eccentricity and corneal diameter measured by Placido‐based topography is a valid predictor of the corneoscleral sagittal height in healthy eyes. Scleral toricity and axis of the flattest meridian seem to be independent from Placido‐based corneal parameters and requires additional measuring tools.
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