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Editors Selection IGR 18-3
Anatomical Structures: Visualizing ONH structures in OCT images
Comment by Michele Iester on:
71463 A Digital Staining Algorithm for Optical Coherence Tomography Images of the Optic Nerve Head, Mari JM; Aung T; Cheng CY et al., Translational vision science & technology, 2017; 6: 8
Jean-Martial Mari et al. have reported the results of a new method to analyse optic nerve head (ONH) and highlight either connective or neural tissue by using spectral domain optical coherence tomography (OCT). This new algorithm was verified with a digital phantom, compared with a modern clustering algorithm, and tested in 10 subjects with consistent digital stains.
It has been shown that in healthy ONHs the proportion of connective and neural tissue can change on the basis of the position: in the anterior part neural tissue is about 90%, while 10% in the posterior part. Connective tissues are the main load bearing elements of the ONH, and there is evidence to suggest that biomechanical and/or morphologic features of these tissues may serve as strong biomarkers for glaucoma, as the authors mentioned in their work.
There is evidence to suggest that biomechanical and/or morphologic features of these tissues may serve as strong biomarkers for glaucoma.
In previous studies, different authors have shown structural changes, such as collagen types, which can change from a long chain to a short one in glaucomatous patients, direction of the collagen fibres, or change in elastin production, which could alter the biomechanical proprieties of the connective tissue and in particular of the lamina cribrosa (LC). Besides in previous studies it has been shown that LC changes morphologically and morphometrically its shape in glaucomatous patients, even after a surgical approach the LC tends to invert its shape for IOP changes. In a recent study, Yang et al. summarized that the main connective tissue changes associated with chronic IOP elevation in a monkey model were post-laminar deformation, laminar thickening, scleral canal expansion, laminar migration, and scleral bowing, outlining the importance of monitoring connective tissue behaviour in vivo. Thus, because ONH connective and neural tissues are altered in glaucoma, digital staining might be of interest in the clinical management of glaucoma.
Using OCT images of the ONH, they found that this new algorithm could be able to isolate connective tissues, prelaminar tissues and the nerve fibre layer, or other retinal layers, as four separate digitally stained volumes, and that connective tissues of the ONH were highly visible in the digitally stained images. We spent many years before having retinal segmentation programs, but now we start to have new data to improve our clinical approach. Automated segmentation of the LC and of the choroidal vessels has remained a challenge, and only few solutions, sometimes complex, have been proposed. However this is beyond the scope of this paper, but in future a simple segmentation algorithms could be combined with digital staining to automatically identify structures such as the anterior LC surface or the choroidal vessels. This is a prelaminar study and there are some points that need to be considered such as the small number of included patients, the type of included patients and the absence of correlation with the human histology for lack of available data. Besides there are some technical limitation that the authors mention in discussion, but they will work on in the next future. This study is another step forward in the analysis of the deeper ocular structures.
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