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Editors Selection IGR 13-2

Examination methods: Doppler flowmetry and IOP manipulation

Comment by Alon Harris on:

19639 Regulation of choroidal blood flow during combined changes in intraocular pressure and arterial blood pressure, Polska E; Simader C; Weigert G et al., Investigative Ophthalmology and Visual Science, 2007; 48: 3768-3774

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Primary open-angle glaucoma (OAG) is a multi-factorial optic neuropathy characterized by progressive retinal ganglion cell death and associated visual field loss. While intraocular pressure (IOP) remains the major risk factor for OAG, clinical evidence suggests reduced ocular blood flow in certain individuals contributes to glaucomatous pathophysiology. Chronic ocular ischemia may be due to faulty vascular autoregulation and/or the inability of the vasculature to overcome elevated IOP to maintain adequate perfusion. Polska et al. (958) have investigated the autoregulatory control of choroidal blood flow in relation to IOP and mean arterial pressure (MAP) in healthy young subjects (n = 17). The authors utilized laser Doppler flowmetry to evaluate choroidal blood flow during IOP (suction cup method)¹ and MAP (squatting) elevation. The authors found that the choroid exhibits some autoregulatory capacity in relation to ocular perfusion pressure (OPP = 2/3MAP-IOP) changes, more so during MAP than IOP manipulations. These results contribute to previously published studies² which show the short posterior ciliary arteries (which supply the optic nerve head (ONH)) are unable to maintain constant perfusion during large IOP increases. As IOP, blood pressure (BP) and thus OPP are known to exhibit diurnal fluctuations in normal tension glaucoma patients,³ periods of high IOP and/or low BP may result in low OPP creating mild chronic ischemia to the ONH which choroidal autoregulation cannot compensate for.

A comprehensive approach to ocular blood flow assessment is recommended to better represent the eye's overall vascular response to stimulus

In the present study, the use of laser Doppler flowmetry to assess choroidal blood flow is a concern as low flow rates and loss of fixation greatly limits subject inclusion and interpretation. A comprehensive approach to ocular blood flow assessment is recommended to eliminate steal phenomenon and better represent the eye's overall vascular response to stimulus. Another limitation is that the present study utilized only young healthy males, while the aging OAG patient's vasculature likely responds differently if not more pathologically. Future research should stress a comprehensive multi-imaging technology approach and utilize OAG patients with age-matched healthy controls.

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