Six–Month Variability (Reproducibility) of Structural and Functional Parameters of Glaucomatous Damage in the Glaucoma Longitudinal Imaging Study (GILS)

Abstract

 

Abstract:

 

To assess progression of glaucoma, changes in structural and functional measurements must exceed measurement error (reproducibility). We determined the 6 month variability in perimetric, optic disc, and macular thickness parameters in the Glaucoma Imaging Longitudinal Study (GILS).

 

Participants in the GILS are examined at baseline and every 6 months by optic disc imaging (HRT II), macular retinal thickness measurement (RTA), and visual field testing (HFA II SITA Fast). Measurements at study baseline and the 6–month visit were used to assess 6–month variability for 140 eyes of 140 GILS patients with good–quality HRT and RTA images and reliable visual fields. Variability was defined using the standard method for computing reproducibility, i.e., the standard error of measurement (Fleiss, Design and Analysis of Clinical Experiments, 1986), considering the 6–month visit to be the "replicate" measurement. Significant change was then defined as two times the reproducibility.

 

 

 

^{Changes exceeding 3.3 dB for MD, 2.1 dB for PSD, 0.34 mm2 for rim area, 0.12 for cup shape measure, and 28 µm and 34 µm for inferior and superior macular thickness, respectively, are unlikely to be due solely to measurement variability and may be a good indication of true progression for each of these parameters.}

 

 

Keywords: clinical (human) or epidemiologic studies: risk factor assessment • imaging/image analysis: clinical