TY - JOUR
T1 - Comparison of three videokeratoscopes in measurement of toric test surfaces
AU - Greivenkamp, John E.
AU - Mellinger, Mark D.
AU - Snyder, Robert W.
AU - Schwiegerling, James T.
AU - Lowman, Andrew E.
AU - Miller, Joseph M.
PY - 1996/2
Y1 - 1996/2
N2 - PURPOSE: We compared the accuracy of the Computed Anatomy TMS-1 (1.41), the EyeSys Laboratories Corneal Analysis System (2.1), and the Visioptic EH- 270 (3.0) videokeratoscopes in measuring toric surfaces. These non- rotationally symmetric aspheric surfaces served as models of corneal astigmatism. METHODS: Precision diamond-turned toric surfaces modeling 0.00 diopter (D) to 7.00 D of astigmatism were fabricated. A three-dimensional contact profiler was developed to calibrate the aspheric surfaces. Videokeratoscopic data taken at 'best focus' were compared to the theoretical shape to quantify device measurement errors. RESULTS: The Computed Anatomy system measurement accuracy shows no statistically significant correlation between measurement error and surface toricity (r2<0.13). Measurement error increased linearly with surface astigmatism for the EyeSys Laboratories system (0.12 D rms error per D of astigmatism, r2>0.96, p<0.001 and the Visioptic system (0.03 D error per D of astimatism, r2=0.88, p<0.001). CONCLUSIONS: This study found systematic performance differences among the three machines. Under ideal alignment conditions, the Computed Anatomy TMS-1 is more accurate at detecting astigmatism. The EyeSys Laboratories Corneal Analysis System apparently underestimates the amount of surface astigmatism because of excessive data smoothing. The Visioptic EH-270 errors are primarily in the central zones and may be due to ring localization errors.
AB - PURPOSE: We compared the accuracy of the Computed Anatomy TMS-1 (1.41), the EyeSys Laboratories Corneal Analysis System (2.1), and the Visioptic EH- 270 (3.0) videokeratoscopes in measuring toric surfaces. These non- rotationally symmetric aspheric surfaces served as models of corneal astigmatism. METHODS: Precision diamond-turned toric surfaces modeling 0.00 diopter (D) to 7.00 D of astigmatism were fabricated. A three-dimensional contact profiler was developed to calibrate the aspheric surfaces. Videokeratoscopic data taken at 'best focus' were compared to the theoretical shape to quantify device measurement errors. RESULTS: The Computed Anatomy system measurement accuracy shows no statistically significant correlation between measurement error and surface toricity (r2<0.13). Measurement error increased linearly with surface astigmatism for the EyeSys Laboratories system (0.12 D rms error per D of astigmatism, r2>0.96, p<0.001 and the Visioptic system (0.03 D error per D of astimatism, r2=0.88, p<0.001). CONCLUSIONS: This study found systematic performance differences among the three machines. Under ideal alignment conditions, the Computed Anatomy TMS-1 is more accurate at detecting astigmatism. The EyeSys Laboratories Corneal Analysis System apparently underestimates the amount of surface astigmatism because of excessive data smoothing. The Visioptic EH-270 errors are primarily in the central zones and may be due to ring localization errors.
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M3 - Article
C2 - 8653525
AN - SCOPUS:0030005745
SN - 0883-0444
VL - 12
SP - 229
EP - 239
JO - Journal of Refractive Surgery
JF - Journal of Refractive Surgery
IS - 2
ER -