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V. A. Sicam, P. N. D. Simpson, M. Mensink, M. Zaal; Accuracy and Precision of a Color Coded Multiple Point Source Specular Reflection Corneal Topographer. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5691.
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It is known that specular reflection topographers measures corneal aberrations more precisely compared to slit imaging instruments (Braaf et. al. OVS 2009 86(5): 467-75). This study determines the accuracy and precision of a new specular reflection corneal topographer (prototype, iOptics, Rijswijk, The Netherlands).
The prototype topographer uses 672 LEDs as stimulator for corneal reflection. The LED pattern has a color code involving the variation in arrangement of three LED colors: RED, YELLOW and GREEN LEDs. This ensures that there is no mismatch in source and image points. Thus, it is free from skew ray error in corneal surface reconstruction encountered in Placido based topographers (Rand et. al. OVS 1997 74(11): 926-30). Measurements of artificial spherical lenses using Spherotronic-trioptics spherometers are used as a gold standard for comparison. Other artficial surfaces such as toric and trefoil surfaces were measured and their residual corneal aberrations were assessed. To evaluate precision of eye measurements, 10 repeated measurements were done on three eyes with no corneal abnormality. For comparison this procedure was also done using the Pentacam rotating scheimpflug camera (Oculus, Wetzlar, Germany).
The difference between the corneal height measurement between the prototype topographer and spherotronic trioptics spherometer is < 0.8 microm. The spherometer measures corneal height with precision (SD of four trials) < 0.1 microm. This is equivalent to corneal aberration precision < 0.04 microm. Residual corneal aberration (for each Zernike component: astigmatic, coma, trefoil, quadrafoil at 6 mm corneal zone) measured from all surfaces is less than 0.2 microm. Precision of corneal elevation measured by the prototype topographer is 0.8 microm and that of the Pentacam is 1.7 microm.
This new topographer measures corneal height and corneal aberrations with an accuracy of 0.8 and 0.2 microm respectively. And as expected from what is previously known, it is more precise than slit-imaging corneal topographers.
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