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Editors Selection IGR 13-2

Clinical Examination Methods: Bloodflow measurements

Comment by Alon Harris on:

55438 Retinal blood flow in glaucomatous eyes with single-hemifield damage, Sehi M; Goharian I; Konduru R et al., Ophthalmology, 2014; 121: 750-758

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Vascular considerations in glaucomatous optic neuropathy remain at the forefront of research paradigms involving non-pressure related damage to the optic nerve and retinal ganglion cells. Numerous novel investigations reveal new insights and confirm older pilot work that ischemia, faulty autoregulation and metabolism defects contribute to glaucoma pathophysisology in many individuals. Compounding the dynamic of these studies is the fact that the intraocular pressure (IOP), glaucoma-induced cellular damage and ocular hemodynamics are not singularly exclusive, as one physiological factor may influence the others. Sehi and colleagues contribute nicely to this body of work by identifying that retinal blood flow (RBF) is significantly reduced in the hemisphere associated with the abnormal hemifield in glaucomatous eyes with single-hemifield damage. Further, the researchers found reduced RBF was associated with thinning of the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) in the corresponding abnormal hemisphere. Interestingly, RBF in the hemisphere with apparently normal visual field was reduced compared with the mean hemispheric flow in healthy eyes. This novel finding suggests vascular alterations occur prior to visual field loss and may be a primary insult and not only a byproduct of metabolic demand regression from glaucomatous cell death. The unique study design of single hemifield damaged glaucoma patients represents a distinctive strength of the study. Other advantages of the author's approach are the use of structural and functional assessment of glaucoma pathology, the inclusion of healthy controls, and multi-center participation. One area of limitation is the lack of multi-point diurnal assessment, as IOP, blood pressure and RBF are known to fluctuate, another is a lack of predictability of RBF-initiated progression of glaucoma which can only be evaluated with a properly designed longitudinal study. Overall, the evidence presented is novel and intriguing, and the presence of reduced RBF in normal field glaucomatous eyes represents a compelling argument for the need of long-term vascular assessments in glaucoma, especially in terms of hemodynamic influenced glaucoma progression.

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