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K. Mohammadi, F. A. Medeiros, L. M. Alencar, L. M. Zangwill, R. N. Weinreb; Long-Term Variability of Hrt 3 Glaucoma Probability Scores in Glaucoma Suspects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3327.
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To evaluate the long-term variability of confocal scanning laser ophthalmoscopy (HRT 3, Heidelberg Engineering GmbH, Dossenheim, Germany) glaucoma probability score (GPS) values in glaucoma suspects.
The study enrolled a cohort of untreated glaucoma suspects from the Diagnostic Innovations in Glaucoma Study (DIGS) who did not develop any evidence of visual field damage or change in the appearance of the optic nerve (as evaluated by stereophotographs) during an average follow-up of 9.4 Â± 3.2 years. Subjects underwent ocular imaging using the commercially available HRT II (with HRT 3 software). At each visit, each eye was imaged 3 times and a mean topographic image was obtained. Subjects underwent repeated testing with HRT at approximately 12 month intervals during their follow-up. In total, 130 exams were obtained in 34 eyes of 34 individuals during an average HRT follow-up time of 42.1 Â± 15.9 months. Due to the relatively recent introduction of the HRT II, the follow-up time with this instrument was considerably lower than the total follow-up time as part of the DIGS study. A random effects analysis of variance model was used to estimate intraclass correlation coefficients (ICCs) and intervisit standard deviations. Long-term test-retest variability was calculated as 1.96 times the intervisit standard deviation.
ICC and long-term variability estimates (95% CI) for the global GPS were 0.86 (0.78 â€" 0.92) and 0.20 (0.18 â€" 0.24). For segmental GPS parameters, ICCs ranged from 0.85 to 0.91 and long-term variability estimates ranged from 0.17 to 0.22. ICCs for the optic nerve and retinal nerve fiber layer (RNFL) shape parameters were 0.96 (cup depth), 0.80 (rim steepness), 0.79 (cup size), 0.92 (horizontal RNFL curvature) and 0.90 (vertical RNFL curvature).
Objective optic nerve assessment using the glaucoma probability score showed good long-term reproducibility in glaucoma suspects. However, it is important to consider that changes of up to 0.2 (20%) in the global GPS measurements obtained during long-term follow-up could still be attributed to instrument variability.
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