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Erschienen in:
01.11.2009 | Glaucoma
Reproducibility of color Doppler imaging
Erschienen in: Graefe's Archive for Clinical and Experimental Ophthalmology | Ausgabe 11/2009
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Purpose
The aims of this study were: (1) to determine the intra-subject and inter-observer variability of color Doppler imaging (CDI) measurements and readings of the retrobulbar blood vessels, (2) to compare the difference in variability of CDI parameters in non-glaucomatous controls versus glaucoma patients, and (3) to provide calculations of minimum sample sizes for future CDI studies.
Methods
Patients with normal tension glaucoma (n = 28), primary open-angle glaucoma (n = 19) and non-glaucomatous controls of comparable age (n = 22) underwent CDI on two occasions 1 month apart. Variability in CDI parameters was quantified using (within-subject) coefficients of variation. Based on this variability, minimum sample sizes were calculated to guide the design of future studies comparing CDI between and within groups.
Results
In general, within-subject coefficients of variation for measurements 1 month apart were comparable to previously reported short-term variations. Variability was higher in glaucoma patients than in non-glaucomatous controls. The minimum sample size required for glaucomatous study populations is larger than for non-glaucomatous controls. Smaller patient groups are required to detect change using the peak systolic blood flow velocities than using end diastolic velocities. Studies using a cross-over design require smaller sample sizes than studies with a pre-post or particularly parallel design.
Conclusions
This study provides extensive information on long-term intra-subject variability of CDI measurements in non-glaucomatous controls as well as glaucoma patients. Moreover, sample size calculations are provided for studies involving glaucoma patients as well as non-glaucomatous individuals, using three different commonly used study designs.