Optimization model for UV-riboflavin corneal cross-linking.

Purpose: To develop a theoretical model for riboflavin ultraviolet-A cross-linking treatment that can predict the increase in stiffness of the corneal tissue as a function of the ultraviolet intensity and riboflavin concentration distribution, as well as the treatment time.

Methods: A theoretical model for calculating the increase in corneal cross-linking (polymerization rate) was derived using Fick's second law of diffusion, Lambert-Beer's law of light absorption, and a photopolymerization rate equation. Stress-strain experiments to determine Young's modulus at 5% strain were performed on 43 sets of paired porcine corneal strips at different intensities (3-7 mW/cm²) and different riboflavin concentrations (0.

Optical ray tracing for the calculation of optimized corneal ablation profiles in refractive treatment planning.

Purpose: Optical calculations have shown that wavefront-based ablation profiles as well as intraocular lens (IOL) implantations can cause residual aberrations or even induce significant additional aberrations due to the poor registry between the eye's optical components. These effects can be exacerbated in eyes that require higher corrections. Individualized eye models can provide accurate ablation profiles for these cases.

Corneal and total wavefront aberrations in phakic and pseudophakic eyes after implantation of monofocal foldable intraocular lenses.

Purpose: To compare the correlation between corneal and total wavefront aberrations in normal phakic and pseudophakic eyes after implantation of foldable monofocal intraocular lenses (IOLs).

Setting: University Hospital, Eye Clinic, Zurich, Switzerland.

Methods: Wavefront aberrations and corneal topography of 29 eyes that had cataract surgery with implantation of hydrophobic monofocal foldable IOL (AcrySof, Alcon Labs) were measured at least 2 months postoperatively and compared with wavefront measurements performed in 33 normal young phakic eyes.

The effect of phenylephrine and cyclopentolate on objective wavefront measurements.

Purpose: To investigate the impact of phenylephrine and cyclopentolate on wavefront refraction and fourth order spherical aberration C12.

Methods: This cohort study comprised 151 eyes with sphere up to -10.00 diopters (D) and cylinder -3.

Treatment-induced shifts of ocular reference axes used for measurement centration.

Purpose: To determine the shifts of the main corneal reference points in dependence of the chosen centration axis for the treatment.

Setting: Federal Institute of Technology Zurich, Institute of Biomedical Engineering, Zurich, Switzerland.

Methods: Computer simulations were performed on several variants of the Gullstrand-Emsley schematic eye, which was modified by an off-axis fovea.

Simulation of eye-tracker latency, spot size, and ablation pulse depth on the correction of higher order wavefront aberrations with scanning spot laser systems.

Purpose: The aim of this theoretical work was to investigate the robustness of scanning spot laser treatments with different laser spot diameters and peak ablation depths in case of incomplete compensation of eye movements due to eye-tracker latency.

Methods: Scanning spot corrections of 3rd to 5th Zernike order wavefront errors were numerically simulated. Measured eye-movement data were used to calculate the positioning error of each laser shot assuming eye-tracker latencies of 0, 5, 30, and 100 ms, and for the case of no eye tracking.

Transferring wavefront measurements into corneal ablations: an overview of related topics.

We give an overview of possible side effects that are specific for, or of particular relevance in, customized treatments. Certain processes involved in customized ablations have the potential to alter the quality of the optical correction. Professionals associated with customized treatment should be informed and trained with respect to possible sources of error.

Limitations of pupil tracking in refractive surgery: systematic error in determination of corneal locations.

Purpose: The goal of this investigation was to show the theoretical limitations of pupil tracking in refractive surgery. The parallax error associated with localizing corneal positions by tracking the subjacent entrance pupil center was quantified.

Methods: Optical ray-tracing in a schematic model eye was performed to determine the geometric parallax error.

Maximum permissible torsional misalignment in aberration-sensing and wavefront-guided corneal ablation.

Purpose: To determine the maximum permissible torsional misalignment in wavefront-guided refractive surgery.

Setting: University of Zurich, Department of Ophthalmology, Zurich, Switzerland.

Methods: The effect of torsionally misaligned ablations on the optical outcome was simulated using measured wavefront aberration patterns (2nd to 6th orders) in 130 normally aberrated eyes.

Correlation between corneal and total wavefront aberrations in myopic eyes.

Purpose: Corneal topography data expressed as corneal aberrations are frequently used to report corneal laser surgery results. However, the optical image quality depends on all optical elements of the eye, including the human lens. We investigated correlations between corneal and total wavefront aberrations and the relevance of corneal aberrations for representing the optical quality of the total eye.

Optimal visual perception and detection of oral cavity neoplasia.

The most common way to detect disease is by visual inspection of the suspect tissue. However, the human eye is not optimized for this task because the perceived spectrum of light is divided into three channels, all of which have overlapping spectral sensitivity curves. Here, we present new methods to optimize visually perceived contrast based on spectral differences between normal and abnormal tissue.

Maximum permissible lateral decentration in aberration-sensing and wavefront-guided corneal ablation.

Purpose: To investigate the lateral alignment accuracy needed in wavefront-guided refractive surgery to improve the ocular optics to a desired level in a percentage of normally aberrated eyes.

Setting: Department of Ophthalmology, University of Zurich, Zurich, Switzerland.

Methods: The effect of laterally misaligned ablations on the optical outcome was simulated using measured wavefront aberration patterns from 130 normal eyes.

Experimental results of preparing laser-shaped stromal implants for laser-assisted intrastromal keratophakia in extremely complicated laser in situ keratomileusis cases.

Purpose: To evaluate the feasibility of laser-shaped stromal implants from a donor eye for correcting extreme high hyperopia with irregular astigmatism and an exceptionally thin corneal bed.

Methods: Thirty-one fresh enucleated porcine eyes were used. The procedure was initiated with mechanical de-epithelialization followed by a lamellar cut with a microkeratome, resulting in a hinged flap (thickness 150 microm, diameter 9.

Aberration-sensing and wavefront-guided laser in situ keratomileusis: management of decentered ablation.

Purpose: To clarify the feasibility of aberration-sensing and wavefront-guided laser in situ keratomileusis (LASIK) to manage grossly decentered ablation and to discuss the limitations of the technology.

Methods: Three patients with previous decentrations of the ablation zone between 1.5 to 2.