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Stephan Holzer, Hemma Resch, Clemens Vass; Repeatability of triple exams of GDx ECC measurements in glaucoma and glaucoma suspects. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4560.
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© ARVO (1962-2015); The Authors (2016-present)
Scanning laser polarimetry using the enhanced cornea compensation (ECC) is still an important tool for supporting the diagnosis and observing the state of glaucoma. Despite the manufacturer recommendation to use triple exams (means of three measurements) for longitudinal observation, to date there is no published evidence regarding the repeatability of such triple exams compared to the single GDx exams. Our aim was to retrospectively analyze under non-study settings the benefit of intrasession triple exams of GDx in terms of better repeatability when compared to single measurements.
To the manufacturer's recommendation at a baseline glaucoma visit we acquired 2 sets of 3 records using GDx ECC© (Carl Zeiss Meditec AG) in 275 subjects (OD=275 OS=270; age 10 to 85 years) in the setting of a private practice of an experienced glaucoma specialist. The data of the 6 single measurements and the 2 associated means of 3 images (triple exams) were retrospectively statistically analyzed in terms of repeatability.
For the single images (SI) and the mean images (MI) the mean thickness values (+- standard deviation) were: for the TSNIT average 47.34µm (+-6.22) and 46.96µm (+-6.23), the superior 57.36µm (+-9.42) and 56.97µm (+-9.44), and for the inferior area 59.59µm (+-9.55) and 59.25µm (+-9.56).<br /> The coefficients of variation (CoV) for the SI and the MI were: for the TSNIT average 2.27% and 1.35%, the superior 3.21% and 1.78%, and for the inferior area 2.97% and 1.72%. All the CoV values were significantly smaller for the MI compared to the SI. On average the CoV was reduced by 42%
Single measurements repeatability appears to be similar to published results of spectral domain optical coherence tomography (SD-OCT) repeatability when the measurement circle of the OCT retest was manually set. The repeatability of the mean images was considerably better and well comparable to the published results of SD-OCT where the retest was acquired as follow up examination.
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