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G. A. Cull, Y. Liang, C. F. Burgoyne, L. Wang, G. A. Cioffi; Static Autoregulation of the Optic Nerve Head in Normal Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5856.
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To study the normal static autoregulation of the optic nerve head (ONH) at different intraocular pressures (IOP) in Rhesus monkeys to allow the development of an autoregulation curve and to assess inter-eye and inter-animal differences.
In both eyes of pentobarbital anesthetized rhesus monkey (n=4), two needles were inserted into the anterior chamber: one was connected to a saline reservoir to set the intraocular pressure (IOP) at 10 mmHg; the other to record the actual IOP. While mean blood pressure (MBP) was monitored continuously and maintained between 75-100 mmHg, IOP was elevated to 30, 40, 50, and 55 mmHg over 1.0 -1.5 seconds as follows. First static normalized blur rate (NBR), representing an estimate of ONH blood flow, was recorded with a laser speckle flowgraphy (LSFG) (Softcare, Japan) at 10 mmHg and 5 minutes after each IOP increase. Second, following the high IOP LSFG imaging time point IOP was lowered back to 10 mmHg for 5 minutes before increasing the IOP to the next level. A normal autoregulation curve was plotted using actual NBR changes at each increase in IOP. Ocular perfusion pressure (OPP) was calculated by the formula: OPP =(MBP - 5mmHg) - IOP. A factorial ANOVA (Statistica) was performed to test differences between monkeys, eyes, and IOP levels.
Mean MBP during testing was 83.5 ± 6 (SD) mmHg. There was no significant difference (p=0.97) in NBR between left and right eyes of any of the monkeys at any level of IOP. There was a significant difference in NBR between animals (p < 0.001). No significant change occurred in NBR until IOP was greater than 40mm Hg or OPP was less than 39 ± 6 SD. Figure1 showes the mean NBR of 4 monkeys at IOP 10, 30, 40, 50 and 55 mmHg.
The capacity of autoregulation in the ONH can be quantitatively assessed with parameters measured during a static blood flow response to a rapid IOP increase with the current technique. The autoregulatory capacity decreases when IOP is greater than 40 mmHg (OPP < 39). Because no significant difference was found in NBR between left and right eyes, one eye can be used as a contralateral control when studying the status of autoregulation in disease models induced in one eye, such as experimental glaucoma.
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