Synchronous phase-demodulation of high spatial frequency, concentric-rings, Placido fringe patterns

TL;DR

This paper introduces a synchronous phase-demodulation technique for high spatial frequency concentric-ring Placido fringe patterns, enhancing wavefront testing and corneal irregularity measurement with improved sensitivity and efficiency.

Contribution

It proposes a novel synchronous demodulation method for high-frequency Placido patterns, enabling single-image wavefront slope estimation for improved accuracy in corneal and wavefront analysis.

Findings

Effective phase-demodulation of high-frequency patterns achieved

Single radial slope image suffices for full wavefront reconstruction

Enhanced sensitivity in wavefront and corneal irregularity testing

Abstract

Here a synchronous phase-demodulation method for high spatial frequency (HSF), concentric-rings Placido fringe pattern is proposed. The earliest use of this concentric-rings pattern was to gauge non-spherical irregularities of the human cornea by Portuguese ophthalmologist Antonio Placido in 1880. Most modern corneal topographers use Placido patterns to test human cornea irregularities; a field of application of this paper. Another field of application of HSF conic-carrier fringe patterns is to test wavefronts using what may be called the Placido-Hartmann screen test. These screens would be formed by periodic concentric ring apertures. A Placido-Hartmann test would be sensitive to the radial slope of the wavefront under measurement. Finally as in the Hartmann-Shack test, one may use a radial lenslet array of toroidal-shaped lenses to test the radial slope of a wavefront at the focal plane. The main advantage of estimating the radial slope of a wavefront using a HSF Placido pattern is that a single radial slope image is sufficient to integrate the full wavefront shape.