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Editors Selection IGR 12-2
Structural Examination Methods: The potential of HD-OCT
Comment by Robert Fechtner on:
27178 Retinal nerve fiber layer imaging with spectral-domain optical coherence tomography: Analysis of the retinal nerve fiber layer map for glaucoma detection, Leung CKS; Lam S; Weinreb RN et al., Ophthalmology, 2010; 117: 1684-1691
As diagnostic technology evolves we, as clinicians, are often struggling to understand whether the technologic advances translate into clinical utility. The last few years have seen the introduction of spectral domain optical coherence tomography (SD-OCT) as a replacement for time domain (TD-OCT). The retina community has quickly embraced SD-OCT for the beauty and resolution of the images provided. In this application, the data seem to be subjected more to qualitative than quantitative analysis. In contrast, the glaucoma community depends on the software tools that accompany these technologies either to distinguish abnormality (usually compared to a normative data base) or to detect progression. In the study by Leung et al. (1710) the retinal nerve fiber layer (RNFL) thickness deviation map from an SD-OCT (Cirrus HD-OCT), was compared with circumpapillary RNFL measurements from a TD-OCT (Stratus OCT). The thickness deviation maps appear familiar due to the similarity in appearance to output from current scanning laser polarimeter. However, the technologies underlying data acquisition are not at all similar. Subjects for this study were recruited at the University Eye Center at the Chinese University of Hong Kong. Appropriate inclusion and exclusion criteria were established. As would be expected from this experienced research collaboration, glaucoma was defined based on the presence of visual field defects. This topic has been discussed in these pages before. I will only comment that this may offer a bias of excluding very early glaucoma and might improve the specificity of structural testing. Analysis of the RNFL thickness deviation map was not available in the commercially released software. For this study, the investigators developed a scoring system. Both SD-OCT and TD-OCT attained relatively high specificity and sensitivity. However, analysis of the RNFL thickness deviation map improves the sensitivity at a high level of specificity compared with circumpapillary RNFL measurement. The scoring system developed to interpret the RNFL thickness map outperformed conventional analysis. Innovations such as this that come from productive and thoughtful researchers can advance our clinical care if they are then confirmed and made available for the commercial instruments. We have seen this happen with scanning laser topography. The potential of HD-OCT for glaucoma care will be more fully realized through the evolution of software tools. This study points out one avenue for such progress.
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