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Editors Selection IGR 16-1

Clinical Examination Methods: Measuring ONH perfusion

Comment by Lin Wang on:

56439 Optical Coherence Tomography Angiography of Optic Disc Perfusion in Glaucoma, Jia Y; Wei E; Wang X et al., Ophthalmology, 2014; 121: 1322-1332

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Dr. Jia and colleagues have compared optic nerve head (ONH) perfusion between normal and glaucoma subjects, using a high-speed swept-source OCT instrument and a split-spectrum amplitude-decorrelation angiography (SSADA) algorithm developed in their lab. With the technique an exquisite 3-D ONH vascular architecture image is generated to quantify the ONH perfusion with optic disc flow index, a computed arbitrary unit. These results show several important findings. Firstly, in addition to excellent intra- and intervisit repeatability measured by this technique, it reveals that the inter-subject variability of the optic disc flow index in the normal population is much lower (5.0%, coefficient of variance) than the other instruments.

Glaucoma eyes had attenuated flow both in the superficial disc and in the deeper lamina cribrosa

While the ocular perfusion pressure in these same subjects has a large variation, this suggests that the ONH blood flow is well regulated and maintained within a relatively narrow range. With this exceptionally tight inter-subject variability, improved from their previous work by using this latest iteration of the cutting-edge technology, a 25% lower flow index in the glaucoma group can be effectively discerned with 100% sensitivity and specificity. Secondly, the 3-D angiography allows the optic nerve head perfusion to be projected onto en face views in 3 layers (retinal, choroidal and scleral/lamina cribrosa). Although each layer was not quantitatively compared between normal and glaucoma, evaluation based on the 3D angiography images suggests that glaucoma eyes had attenuated flow both in the superficial disc and in the deeper lamina cribrosa. This finding provides important clinical evidence of insufficient blood flow perfusion deep within the glaucomatous lamina cribrosa, one of the important issues regarding the measurement from all optically-based blood flowmeters. In spite of the limitations that have been thoroughly discussed in the paper, this study represents important progress which increases the toolset we can use to understand the hemodynamic changes in the ONH in glaucoma.

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