Purpose:
Idiopathic bilateral optic atrophy (BOA) of rhesus macaques is a disease affecting primarily macular ganglion cells, causing thinning of the retinal nerve fiber layer (RNFL) of papillomacular bundles and temporal optic disk pallor. Histopathology revealed axon loss and gliotic changes within the temporal quadrant of the anterior orbital optic nerve (ON). The purpose of the study was to assess basal blood flow (BF) and autoregulation (AR) within the optic nerve head (ONH) in eyes with BOA.
Methods:
In six BOA and ten normal control (CTL) animals, two needles were inserted into the anterior chamber of both eyes. One needle was to manometrically control the intraocular pressure (IOP); the other was connected to a pressure transducer to measure IOP. A laser speckle flowgraph (Softcare, Japan) was used to measure BF in the ONH. Under stable systemic blood pressure, basal BF was measured while the IOP was set at 10mmHg; AR capacity was assessed by comparing the BF changes after the IOP was raised from 10mmHg to 30mmHg for 3min. Spectral Domain OCT (Spectralis Heidelberg GmbH) was used to measure RNFL thickness (RNFLT). The averaged BF difference was analyzed using ANOVA and the Mann-Whitney test was used to compare the mean RNFLT in each quadrant between BOA and CTL eyes.
Results:
The average RNFLT was 69.9±7.4µm in BOA eyes, which was significantly thinner than in CTL eyes (101.7±12.5µm, P<0.05). The average basal ONH BF was 8.24±1.24 in BOA eyes, which was significantly lower compared with 10.69±1.33 of CTL eyes (P<0.001; see graph). The magnitude of basal BF decrease was positively correlated with RNFLT (P<0.05). After IOP was raised to 30mmHg, BF decreased to 6.72±1.33 (22%, P<0.01) in BOA, but did not change in CTL eyes (10.94±1.38, P=0.18). Blood flow was uniformly reduced in all four quadrants of the ONH despite dominate structural damage in the temporal quadrant (see graph).
Conclusions:
The basal BF and autoregulation capacity in the ONH were significantly reduced. The magnitude of the hemodynamic changes was correlated with RNFLT, and blood flow reduction in BOA eyes were equally decreased in all quadrants.
Keywords: blood supply • optic nerve • immunohistochemistry