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Balwantray C. Chauhan, J. Wade Blanchard, David C. Hamilton, Raymond P. LeBlanc; Technique for Detecting Serial Topographic Changes in the Optic Disc and Peripapillary Retina Using Scanning Laser Tomography. Invest. Ophthalmol. Vis. Sci. 2000;41(3):775-782.
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purpose. To describe and evaluate a new statistical technique for detecting
topographic changes in the optic disc and peripapillary retina measured
with confocal scanning laser tomography.
methods. The 256 × 256-pixel array of topographic height values obtained
with each image from the Heidelberg Retina Tomograph (Heidelberg
Engineering, Heidelberg, Germany) was divided into an array of 64 × 64 superpixels, where each superpixel contained 16 (i.e., 4 ×
4) pixels. An analysis of variance technique was developed to analyze
each superpixel with three baseline and three follow-up images. The
performance of the technique was tested with and without adjustment for
spatial correlation of topographic values using computer simulations
and with real data from a normal control subject and a patient with
progressive glaucomatous disc change.
results. Computer simulation with fixed population means and variance, and
varying spatial correlation showed a monotonically increasing number of
superpixels with significant test results (false positives), with 20%
false-positives when the spatial correlation was 0.8 (the approximate
median value in real patient data). The number of false-positive
results was similar (17%) in serial images of a normal subject. When
corrected for spatial correlation, the number of false-positives was
independent of the level of spatial correlation and remained at the
expected value of less than 5% in both simulations and real data.
Although the number of significant test results in the patient with
progressive glaucoma decreased after correction for spatial
correlation, the change was readily apparent. Statistical power to
detect mean differences in topographic values ranging from 0.5 to 4.0
SDs in computer simulation showed low power for changes of 1 SD or
less, but increased dramatically with larger changes.
conclusions. This technique has a high level of sensitivity to detect changes in the
optic disc while maintaining a high level of
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