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L. Remon, C. Dorronsoro, S. Kling, J. Merayo-LLoves, S. Marcos; Validation of Posterior Cornea Quantitative Scheimpflug Imaging Using a Hybrid Porcine/Plastic Model. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5105.
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© ARVO (1962-2015); The Authors (2016-present)
Quantitative analysis of posterior corneal Scheimpflug images requires proper correction of geometrical and optical distortion from the anterior surfaces. We developed a hybrid porcine/plastic eye model (with the scattering properties and refractive index of corneal tissue and known posterior corneal geometry) for validation of the posterior corneal reconstruction of the Pentacam Scheimpflug imaging system.
The hybrid porcine/plastic eye models consisted on excised porcine corneas mounted on a 12-mm diameter plastic piston finished on spherical surfaces with known radii of curvature (7.47, 7.93 and 8.75 mm, as validated by non-contact profilometry). Special care was taken to preserve the endothelium integrity. The porcine’s posterior cornea conformed to the underlying plastic surface. Scheimpflug images were obtained within 4 hours post-mortem. The posterior corneal surface was evaluated using both fitting routines written in Matlab and Pentacam software. We used 10 porcine corneas (5 repeated measurements per eye). The retrieved posterior corneal geometry was compared to the plastic surfaces’ nominal data. Correlations between anterior and posterior corneal data were performed to assess that the optical distortion correction was successfully applied.
There was a good correspondence between nominal and estimated posterior radii of curvature, although the measured radius was a consistently underestimated (0.26±0.12 mm on average). There was larger variability and underestimation of the posterior surface asphericity (Qpost=-0.33±0.44) than of the same spherical surfaces tested anteriorly (Qant=-0.02±0.22). The anterior porcine corneas varied in anterior radii (from 8.0 to 9.6) and astigmatism (1.9 ±1.0 D). However, there was no significant correlation between anterior and posterior corneal radii of curvature, asphericity or astigmatism (p>0.6).
This model has allowed testing the accuracy of the posterior corneal geometry estimates from Pentacam. The independence of the retrieved data from the anterior corneal topography suggests proper correction of optical distortion. This model shows more comparable properties to those of living eyes and could be used for calibration of other anterior segment imaging systems.
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