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Editors Selection IGR 13-2

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Comment by Alon Harris on:

53854 Longitudinal hemodynamic changes within the optic nerve head in experimental glaucoma, Cull G; Burgoyne CF; Fortune B et al., Investigative Ophthalmology and Visual Science, 2013; 54: 4271-4277

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Reduction of intraocular pressure (IOP) remains the only currently approved treatable risk factor for the prevention of vision loss associated with glaucoma. Numerous other factors have been suggested to be involved in the disease pathophysiology due to glaucoma progression in patients with low IOP and/or significantly reduced IOP. Impaired vascular functionality is at the forefront of non-pressure related risk assessment. It is important to remember, however, that IOP and vascular factors are not necessarily always independent. Cull and associates highlight this in their investigation of longitudinal hemodynamic changes within the optic nerve head (ONH) in experimental glaucoma. The authors found basal ONH blood flow exhibited a two-phase change from early-stage mild blood flow increase to eventual significant decrease, with the latter phase exhibiting strong correlation to retinal nerve fiber layer (RNFL) loss. The authors conclude that compromised ONH blood flow observed in glaucomatous patients with and without high IOP is at least in part the result of neural loss and potentially reduced metabolic demand. A strength of the study is their approach to the experimental glaucoma model with three to five sessions utilized to establish baseline values of IOP, RNFL, and ONH blood flow in each eye. The study also benefited from an ability to carefully control glaucomatous damage and manipulate IOP levels over time. An area of concern in any animal model (15 adult rhesus macaques in the current investigation) is the applicability to human glaucoma physiology and individual vascular autoregulation variability. Their glaucoma model also does not have the ability to account for preexisting ocular ischemia; which has been found in many prospective glaucoma studies even in patients with low IOP. Overall the data is compelling and contributes to our continued understanding of blood flow and IOP relationships to glaucoma damage.

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