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GA Kounis, MK Tsilimbaris, IG Pallikaris; A New Method for the Reproducibility Evaluation of Placido-Based Topographic Systems . Invest. Ophthalmol. Vis. Sci. 2002;43(13):170.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate the reproducibility of computerized topography systems using a novel software, by means of a point-by-point analysis of topographic raw data. Methods: Exams of ten consecutive measurements with the TechnoMed C-Scan topographic system were performed in 5 calibration spheres and 18 human eyes. With each measurement the system calculates the value of refractive power of 10800 corneal points and 108000 values for each exam. All these data were exported in ASCII format. Our software segments the corneal surface in 1200 segments and assigns a refractive power +- standard deviation in each one of them using the refractive power values and polar coordinates exported by the topographic system from each measurement for each exam. The SD was used as the measure of the system reproducibility for each specific segment. The results were presented as colour-coded maps, in a way similar to that of a topographic system. Results:Even though calibration spheres were more reproducible (standard deviation less than 0.25 D in paracentral area) compared to human eyes (more than 0.5 D in paracentral area), the spheres presented areas with standard deviation exceeding 1D. This was more obvious in the in central and peripheral areas of the steepest and flattest spheres (6.5mm and 10 mm). In human eyes the SD of the central corneal area exited 0.25 diopters in a significant number of segments. In addition eyes with high and irregular astigmatism presented areas with Standard deviation exceeded 1 D in central and paracentral corneal areas. Conclusion: Our method gives an estimate of the topography system’s reproducibility, in a way much more detailed than any available module. The color-coded map presentation facilitates interpretation. Further development may permit the application of this module in other commercial Placido - Disc Corneal topographers as well as in recently developed wavefront analysers.
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