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Grant Cull, Chelsea Piper, Claude Burgoyne, Lin Wang; Optic nerve head basal blood flow increases early and then progressively decreases in non-human primate experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4465.
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To study the effect of chronic elevated IOP on optic nerve head (ONH) basal blood flow (bBF) in Non-human Primate (NHP) experimental glaucoma (EG) at progessive stages of retinal nerve fiber layer thickness (RNFLT) loss.
In six adult NHPs, two needles were inserted into the anterior chamber of each eye: one connected to a saline reservoir to set the IOP at 10 mmHg; the other recording the actual IOP. Three or more baseline (BL) ONH bBF measurements (excluding large vessels), in units of mean blur rate (MBR) and RNFLT were measured by Laser Speckle Flowgraphy and Spectral Domain Optical Coherence Tomography, respectively. Chronic IOP elevation in the EG eye was induced by laser treatment of the trabecular meshwork with the contralateral eye serving as control (CTL). Bi-weekly ONH bBF and RNFLT measurements were obtained throughout the follow-up period. NHPs were sacrificed when EG eye RNFLT was 40 - 62% thinner than BL. ONH bBF measurements for both eyes were split in 4 groups based on RNFLT loss in the treatment eye: 1) BL (before laser treatment), 2) RNFLT loss <10%, 3) RNFLT loss between 10% and 40%, and 4) RNFLT loss >40. A repeated measure ANOVA and post hoc LSD test assessed EG vs CTL eye ONH bBF change within and between groups.
Mean (±SD) post-laser IOP was 13.5 ± 2.7mmHg in the CTL eyes and 32 ± 3.8mmHg in the EG eyes During the early stage of EG (RNFLT loss <10%), ONH bBF was significantly increased compared with its BL value (p=0.01 *). As RNFLT decreased further (10-40%), bBF returned to being statistically insignificant from BL (p=0.6). Significant ONH bBF reduction developed (p<0.0001*) once the RNFLT loss was greater than 40%. There was no significant bBF change in the CTL eyes at any stage compared with BL (Fig.1). There was a significant interaction between stage of RNFLT and eyes (p<0.0001).
ONH bBF increases early and then progressively decreases in NHP EG. The early ONH bBF increase may be the result of autoregulation-induced vasodilation that is a response to the challenges of IOP elevation or may itself be evidence for autoregulation dysfunction. Later ONH bBF decreases is likely the result of reduced metabolic demand or autoregulatory capability.
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