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Lin Wang, Chelsea Piper, Grant Cull, Claude Burgoyne; Blood pressure induced dynamic blood flow autoregulation in the optic nerve head of early experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4448.
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Dynamic autoregulation (dAR) refers to a transient blood flow (BF) response to the sudden perfusion pressure changes induced by altering either blood pressure (BP) or intraocular pressure (IOP). The purpose of the study was to test a hypothesis that dAR capacity in the optic nerve head (ONH) is compromised after chronic IOP elevation in non-human primate (NHP) experimental glaucoma (EG).
In one eye of each 12 NHPs, trabecular meshwork was photocoagulated by laser to induce chronic IOP elevation. The follow eye was served as control (Ctl). After IOP elevation, ONH dAR in both eyes was assessed biweekly. Under general anesthesia, BF was recorded continuously by a Laser Speckle Flowgraphy (Softcare, Japan). BP was registered continuously through an arterial line. BP cuffs were placed around the two arms and one thigh. The cuffs were inflated before the starting of BF recording and were simultaneously released after first ten seconds of BF recording to induce a rapid BP drop (ranging from 12 to 23 mmHg) to evoke the dAR response in ONH. The BF measurements continued for an additional 50 seconds (Fig 1). Retinal nerve fiber layer thickness (RNFLT) was measured by Spectral Domain Optical Coherence Tomography at the end of each test. The experimental endpoint was defined as approximately 12% RNFLT loss in the EG eye. dAR parameters were extracted from BF recordings, including: 1) Basal BF-before the cuff release; 2) maximal BF decrease (%) from basal BF; 3) Tr-the amount of time it took to the maximal BF decrease, 4) Kr-the slope of dAR descending curve. The mean between-eye differences of the parameter were compared (Paired Student T-test).
The average IOP was 29 ±11mmHg in EG eyes and 13 ±3mmHg in Ctl (p<0.001) two to six weeks after laser treatment. The cuff deflation induced 17 ±3mmHg of BP drop for EG eyes and 16 ±3mmHg for Ctl eyes (P=0.09). All four dAR parameters were significantly changed in EG eyes compared to control eyes (Table).
These subtle but significant early hemodynamic changes in EG eye suggest that chronic IOP elevation has a significant impact on the vascular system in the ONH, which manifest as compromised BF autoregulation and basal BF increase. These parameters may be further tested in human glaucoma to identify earlier signs of impaired vascular system in ONH.
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