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Published on: September 16, 2025
[Preliminary results of a wide-angle corneal topography system for Placido-based videokeratographers]
Luis Alberto Vieira de Carvalho1
1Laboratório de Optica Oftálmica, Grupo de Optica, Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP, Brasil. lavcf@if.sc.usp.br
Purpose:
To develop the instrumentation and software for wide-angle corneal topography using a Placido-based videokeratographer. The objective is to allow the measurement of a greater area of the cornea using a simple adaptation to the Placido mire.
Methods:
Using the traditional Placido disc of a commercial corneal topographer, 9 LEDs (Light Emitting Diodes) were installed on the conic mire so that the voluntary patient could gaze in different directions. For each direction Placido images were acquired and processed to form, using a sophisticated computer graphics algorithm, a tridimensional map of the whole cornea.
Results:
It was shown that up to 100% more area of the cornea may be mapped using the here described technique. We present results for a spherical surface calibration and also for a highly astigmatic cornea and analyze quantitatively the additional area that is recovered in terms of curvature and true elevation.
Conclusions:
We believe that this new technique opens opportunities for the improvement of other applications which might benefit from this additional information, such as: contact lens adaptation and design improvement, algorithms for customized refractive surgery, among others.
