Author： Riva C.E. Cranstoun S.D. Petrig B.L.
Publisher： Academic Press
ISSN： 0026-2862
Source： Microvascular Research, Vol.52, Iss.3, 1996-11, pp. : 258-269
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Abstract
The effect of decreased ocular mean perfusion pressure (PP m ), defined as mean arterial blood pressure minus intraocular pressure (IOP), on optic nerve head blood flow (F onh ) and on the response of this flow (RF onh ) to diffuse luminance flicker was investigated in 19 anesthetized cats using laser Doppler flowmetry. PP m was decreased by increasing the IOP. The flicker stimulus consisted of 20-msec flashes delivered at 10 Hz for 30-60 sec. It illuminated a 30#° diameter area of the fundus, centered at the optic disk. Decreasing PP m by 10-35% from its resting value resulted in a 23% increase in RF onh (supranormal RF onh ). With further decreases in PP m , RF onh decreased, reaching zero at a PP m below 20 mmHg. F onh remained constant until PP m was <40 mmHg and then decreased thereafter. When PP m was brought back to resting value after having been decreased for ~45 min, F onh first increased by ~380% and then returned to its value at rest within ~4.5 min. At low PP m , hyperoxia decreased F onh by 23% and restored the attenuated RF onh back to the value at resting PP m and hypoxia did not increase F onh , as it did at normal PP m . This study confirms that the optic nerve head circulation is autoregulated over a wide range of PP m and reveals, for the first time, a hyperemic response to a prolonged decrease in PP m . It suggests that hypoxia plays a role in abolishing RF onh at low PP m and that the supranormal RF onh at moderately decreased PP m is due to an increase in the flicker-induced ganglion cell activity.
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