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Glaucoma Dialogue IGR 17-4

Comment

Comment by Chris Leung on:

67306 Structural and Functional Progression in the Early Manifest Glaucoma Trial, Öhnell H; Heijl A; Brenner L et al., Ophthalmology, 2016; 123: 1173-1180

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The Early Manifest Glaucoma Trial (EMGT) is a landmark clinical trial providing important insights into the natural history and management of open-angle glaucoma. In a recent paper, Ohnell and colleagues examined the temporal relationship between detection of optic disc progression and visual field progression in 249 glaucoma patients included in the EMGT and showed that progression in the visual field was detected first more than four times as often as progression in the optic disc in glaucomatous eyes with visual field loss at baseline.

An earlier study using the time-domain OCT has already demonstrated progressive RNFL thinning to be predictive of visual field progression in glaucoma

The ability to detect change in glaucoma depends on the precision and the reliability of the instrument for visual field or optic disc measurement and the frequency of testing. In the EMGT, optic disc progression was determined with monoscopic fundus photographs by three disc readers. Although optic disc photography is essential for documentation of optic disc morphology and detection of optic neuropathies in clinical practice, its reliability for change detection in glaucoma has been questioned. For example, in a study investigating the agreement among glaucoma specialists in determining progressive optic disc changes using optic disc stereophotographs in glaucoma patients, Jampel and colleagues showed a weak inter-observer agreement (Jampel et al., Am J Ophthalmol 2009;147:39-44). Forty percent of cases judged to have progressed in glaucoma severity were found to have the 'worse' optic disc taken at the start of the study. In fact, Ohnell and colleagues reported that the three readers individually changed 'progression' to 'no progression' in 29 cases, 14 cases and 13 cases, respectively. Subtle changes in the neuroretinal rim and the retinal nerve fiber layer (RNFL) can be difficult to discern in optic disc photographs, which may account for the inconsistency in photo grading. The higher frequency of visual field testing in the EMGT may also contribute to the earlier detection of visual field progression compared with optic disc progression. In the EMGT, visual field testing was performed at each study visit (every three months for the first four years and then every three or six months thereafter). By contrast, monoscopic fundus photographs were obtained at baseline, three months, six months and then every six months thereafter. With different frequencies of optic disc photography and perimetry during the study period, examination of the temporal relationship between optic disc and visual field progression would be complicated. Collectively, taking consideration of the signal-to-noise ratio of the measurement of interest and the testing frequency is critical for reliable assessment of optic disc and visual field progression. An earlier study using the time-domain OCT has already demonstrated progressive RNFL thinning to be predictive of visual field progression in glaucoma. While automated white-on-white perimetry has been the standard of visual field testing for more than two decades, the technology of optic disc and RNFL imaging has advanced substantially in recent years. Fourier-domain optical coherence tomography (OCT) measurements of the optic disc and the RNFL have a higher signal-to-noise ratio for change detection compared with reader's assessment of optic disc photographs. An earlier study using the time-domain OCT has already demonstrated progressive RNFL thinning to be predictive of visual field progression in glaucoma (Sehi M, et al. Am J Ophthalmol 2013;155:73-82). It is conceivable that Fourier-domain OCT can outperform time-domain OCT and optic disc photography for analysis of glaucoma progression.

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