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Editors Selection IGR 16-4
Clinical Examination Methods: Glaucoma Detection by OCT
Comment by Don Budenz on:
61553 Estimating the Lead Time Gained by Optical Coherence Tomography in Detecting Glaucoma before Development of Visual Field Defects, Kuang TM; Zhang C; Zangwill LM et al., Ophthalmology, 2015; 122: 2002-2009
Kuang et al. analyzed data of 75 glaucoma suspects who ultimately converted to glaucoma by visual field criteria and 75 normal subjects collected longitudinally as part of the Diagnostic Innovations in Glaucoma Study. Subjects had undergone time domain and then spectral domain OCT as part of the study as well as standard automated perimetry. The investigators found that the glaucoma suspects had thinner average retinal nerve fiber layer (RNFL) thickness up to eight years prior to the development of visual field defects. These findings are consistent with histology studies showing that there is a loss of nerve fibers that precedes detectable visual field loss as currently measured.
Glaucoma suspects had thinner average retinal nerve fiber layer (RNFL) thickness up to eight years prior to the development of visual field defects
It is important to clarify, as the authors also do, that we are not to conclude that all glaucoma suspects showed thinning of the RNFL eight years prior to conversion to glaucoma but that there were detectable differences between the two groups years in advance of conversion. The importance of this study is that the clinician can expect to see RNFL changes before visual field changes in glaucoma suspects over time. An incorrect conclusion of these results would be to treat glaucoma suspects with normal visual field tests just because they have an abnormal RNFL. Because there are many false positives in OCT testing, this practice would result in overtreatment. However, if the clinician sees thinning of the RNFL that is outside the normal thinning expected with aging, this should be considered evidence of glaucomatous change barring any non-glaucomatous conditions that could cause thinning of the RNFL. The study numbers are small between four to eight years but these studies are difficult to perform and the authors are to be commended for collecting longitudinal data of such high quality and the analysis of the data is sound.
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