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G. Fuchsjaeger-Mayrl, L. Schmetterer; Short- Term Reproducibility of Blood Flow Parameters in Healthy and Glaucoma/Ocular Hypertension Subjects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4392.
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Variability is a major problem in ocular blood flow measurements. It is an important determinant of sample size in clinical trials and may limit clinical usefulness if it is too high. Whereas several studies investigated reproducibility of blood flow measurements in healthy subjects, little information is available in glaucoma patients. We set out to compare the short-term reproducibility of blood flow parameters assessed with scanning laser Doppler flowmetry and laser interferometric measurement of fundus pulsation between healthy young subjects and glaucoma patients.
Measurements in 140 healthy male non-smoking subjects and 140 patients with primary open angle glaucoma were included in this analysis. The data from healthy subjects were taken from baseline measurements of various recent clinical studies that were performed in our laboratory in the recent years. The data from glaucoma and ocular hypertension subjects were taken from the baseline measurements of a clinical trial that compared the hemodynamic effects of dorzolamide and timolol. These measurements were taken when patients were washed out for any topical medication. From two consecutive measurements performed within 5 minutes the coefficient of variation in an individual was calculated for each outcome parameter. These included the fundus pulsation amplitude (FPA), the flow, volume and velocity in the rim and the cup.
Mean coefficients of variation were between 3.2% and 23.8 % for all outcome parameters in healthy subjects and between 4.9% and 34.3% in the patients. FPA showed the highest reproducibility although individual coefficients of up to 22.5% and 34.7% were observed in healthy subjects and glaucoma patients, respectively. With scanning laser Doppler flowmetry velocity was better reproducible than volume or flow. Individual coefficients of variation for flow values were as high as 87.5% in healthy subjects and 132.2% in glaucoma/ocular hypertension patients.
Our data indicate that in healthy subjects the selected techniques provide better reproducibility than in patients with ocular disease. This needs to be considered in sample size calculation for clinical trials. In addition, the high individual differences in flow parameter readings observed in some subjects limit the use of the techniques in clinical practice.
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