  This paper presents a novel digital interferometric method to demodulate
Placido fringe patterns. This is a synchronous method which uses a
computer-stored conic-wavefront as demodulating reference. Here we focus on the
experimental aspects to phase-demodulate Placido mires applied to corneal
topography. This synchronous method is applied to two topographic Placido
images and their de-modulated corneal-slope deformation is estimated. This
conic-interferometric method is highly robust against typical "noise" signals
in Placido topography such as: reflected eyelashes and iris structures. That is
because the eyelashes and the iris structures are high frequency "noisy"
signals corrupting the reflected Placido mire, so they are filtered-out by this
method. Digital synchronous interferometry is here applied for the first time
to demodulate corneal topographic concentric-rings images (Patent pending at
the USPTO).
