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.

Forward ray tracing for image projection prediction and surface reconstruction in the evaluation of corneal topography systems.

A forward ray tracing (FRT) model is presented to determine the exact image projection in a general corneal topography system. Consequently, the skew ray error in Placido-based topography is demonstrated. A quantitative analysis comparing FRT-based algorithms and Placido-based algorithms in reconstructing the front surface of the cornea shows that arc step algorithms are more sensitive to noise (imprecise).

Performance in specular reflection and slit-imaging corneal topography.

Purpose: Assessment of the relative performance in measuring corneal shape and corneal aberrations for two specular reflection topographers: Keratron Placido Ring Topographer, VU Topographer, and two slit-lamp imaging instruments: Orbscan II and Topcon SL-45 Scheimpflug.

Methods: Corneal height maps of the anterior corneal surface were obtained from a group of 34 subjects with all four instruments; posterior corneal surface height maps were only obtained with the two slit-lamp imaging instruments. Corneal surface shapes are calculated in terms of radius of curvature and asphericity fitting an aspheric model.

Equivalent refractive index of the human lens upon accommodative response.

Purpose: To experimentally verify the suggestion of Gullstrand (1909), i.e., that the equivalent refractive index of the human lens increases with accommodation.

Development of a ciliary muscle-driven accommodating intraocular lens.

Purpose: To develop a ciliary muscle-driven accommodating intraocular lens (IOL) that has a large and predictable range of variable power as a step toward spectacle independence.

Setting: Department of Physics and Medical Technology, VU University Medical Center, Amsterdam, The Netherlands.

Methods: A concept IOL that has a rotating focus mechanism and a mechanical frame that can operate within the range of ciliary muscle contraction of a typical 60-year-old human eye was designed.