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Impressum
Apex detection with the Orbscan II - the differences in reliability as a function of Myopia, Hyperopia and Astigmatism
Specht H., Rabsilber T., Auffarth G. U., Völcker H. E.
Universitäts-Augenklinik Heidelberg
Introduction: The base for the results in refractive surgery are
the data about height and type of refractive errors, determined by the
corneal topography. Therefore it is crucial that the results of measurement
are reproducible with smallest possible errors. To point out any differences
in dependency of the defective vision we collected and analyzed series
of measurements with the Orbscan II.
Method: Determined was the value of the Apex. The determined data
were collected in each case by three consecutive measurements of an eye
of a patient. 20 highly myopic eyes -9,45dpt (-6dpt to -21,5dpt), 20 hyperopic
eyes +4,825dpt (+3dpt to +7,25dpt) and 20 astigmatic eyes -2,475dpt (-
1,5dpt to -5dpt) were examined. The data of the individual examination
were compared with. In each case the average mean values as well as the
standard deviation (SD) and the status of their variance were determined.
Results: In the group of the myopic eyes the amount of the SD was
+0,4892dpt (+0,0929dpt to +1,0323dpt), the variance was +0,3159 (+0.0086
to +1.0657), the value for the variance coefficient was +1.1012 (+0.2178
to +2.3114). In the group the hyperopic eyes was the amount of the SD
+0,6632dpt (+0,1873dpt to +1,8235dpt), the variance was +0.6028 (+0.0386
to +3.3252), the value for the variance coefficient was +1.5306 (+0.4163
to +2.2254). The group of the astigmatic eyes showed values for the SD
from +0,6941dpt (+0,2163dpt to +1,4493dpt), the value of the variance
was +0.6490 (+0.0264 to +2.1004), this resulted in to a variance coefficient
of +1,5631 (+0.3621 to +4.1167).
Conclusion: The results show differences in the individual measuring
groups. This leads to the possibility that in some of the refractive procedures
based on Orbscan II, especially in the group of the hyperopic as well
as in the astigmatic patient it could come to a larger error dispersion
of the post operative results.