Clinical validation of point-source corneal topography in keratoplasty.

Purpose: To validate the clinical performance of point-source corneal topography (PCT) in postpenetrating keratoplasty (PKP) eyes and to compare it with conventional Placido-based topography.

Methods: Corneal elevation maps of the anterior corneal surface were obtained from 20 post-PKP corneas using PCT (VU topographer, prototype; VU University Medical Center, Amsterdam, The Netherlands) and Placido-based topography (Keratron, Optikon 2000, Rome, Italy). Corneal surface parameters are calculated in terms of radius and asphericity. Corneal aberrations were characterized using standard Zernike convention. An artificial surface with quadrafoil feature (SUMIPRO, Almelo, The Netherlands) was measured and used as a reference to assess instrument performance compared with the gold standard.

Results: The differences (mean ± std of PCT - Placido) found between the two types of topographers in measurements of post-PKP eyes are 0.02 ± 0.21 mm (p=0.64) for radius of curvature, 0.14 ± 0.49 (p=0.23) for asphericity, -0.19 ± 1.67 μm (p=0.61) for corneal astigmatism, -0.25 ± 1.34 μm (p=0.41) for corneal coma, 0.23 ± 0.82 μm (p=0.23) for corneal trefoil, and 0.15 ± 0.28 μm (p=0.02) for corneal quadrafoil. The PCT measured the artificial surface more accurate (rms error 0.16 μm; 0.12 eq. Dpt.) than the Placido-based topographer (rms error 1.50 μm; 1.15 eq. Dpt.).

Conclusions: PCT is more accurate than Placido-based topography in measuring quadrafoil aberration.