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Test-Retest Variability in Structural and Functional Parameters of Glaucoma Damage in the Glaucoma Imaging Longitudinal Study

Jampel, Henry D. MD, MHS*; Vitale, Susan PhD, MHS; Ding, Yulan MS*; Quigley, Harry MD*; Friedman, David MD, MPH*; Congdon, Nathan MD, MPH*; Zeimer, Ran PhD*

Original Article

Purpose To determine the test-retest variability in perimetric, optic disc, and macular thickness parameters in a cohort of treated patients with established glaucoma.

Patients and Methods In this cohort study, the authors analyzed the imaging studies and visual field tests at the baseline and 6-month visits of 162 eyes of 162 participant in the Glaucoma Imaging Longitudinal Study (GILS). They assessed the difference, expressed as the standard error of measurement, of Humphrey field analyzer II (HFA) Swedish Interactive Threshold Algorithm fast, Heidelberg retinal tomograph (HRT) II, and retinal thickness analyzer (RTA) parameters between the two visits and assumed that this difference was due to measurement variability, not pathologic change. A statistically significant change was defined as twice the standard error of measurement.

Results In this cohort of treated glaucoma patients, it was found that statistically significant changes were 3.2 dB for mean deviation (MD), 2.2 for pattern standard deviation (PSD), 0.12 for cup shape measure, 0.26 mm2 for rim area, and 32.8 μm and 31.8 μm for superior and inferior macular thickness, respectively. On the basis of these values, it was estimated that the number of potential progression events detectable in this cohort by the parameters of MD, PSD, cup shape measure, rim area, superior macular thickness, and inferior macular thickness was 7.5, 6.0, 2.3, 5.7, 3.1, and 3.4, respectively.

Conclusions The variability of the measurements of MD, PSD, and rim area, relative to the range of possible values, is less than the variability of cup shape measure or macular thickness measurements. Therefore, the former measurements may be more useful global measurements for assessing progressive glaucoma damage.

*Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD

Division of Epidemiology and Clinical Research, National Eye Institute, NIH, Bethesda, MD

Dr. Jampel is a recipient of a Research to Prevent Blindness Physician Scientist Award.

Supported by NEI grants R01 EY12295 and Wilmer Ophthalmological Institute Core Grant P30 EY01765.

Under a licensing agreement with Talia Technology, Ltd. (Neve Ilan, Israel), Dr. Ran Zeimer is entitled to a share of royalty received on sales of the Retinal Thickness Analyzer described in this article. The terms of this arrangement are being managed by the Johns Hopkins University in accordance with its conflict of interest policies.

Reprints: Henry Jampel, MD, MHS, Woods/Wilmer 377, 600 N. Wolfe St, Baltimore, MD 21287-9205 (e-mail:

Received for publication July 20, 2005; accepted November 18, 2005

© 2006 Lippincott Williams & Wilkins, Inc.