Purpose:
To test the hypothesis that blood flow (BF) and regulation in the anterior and posterior optic nerve head (ONH) regions are altered in EG by using a microspheres method.
Methods:
Unilateral EG was induced in 5 monkeys by laser photocoagulation of trabecular meshwork; the contralateral eye served as control. After retinal nerve fiber layer thickness (RNFLT) measured with OCT was reduced by ~30% (except for one animal), BF was quantified by injection of 60 million fluorescent microspheres (10 µm diameter) into left ventricle while the IOP was set at 40 mmHg in both eyes and BP maintained within 80s mmHg. BF within each anterior (from ONH surface to the posterior boundary of laminar region) and posterior (1 mm of retrolaminar region) ONH was determined and statistically compared between EG and control eyes (Paired Student t-test). The total area of axonal damage to that of normal within each optic nerve of EG eyes was assessed using a neural network postmortemly.
Results:
Mean post-laser IOPs was 27.6±2.5 in the EG and 12.2±7.7 mmHg in the control eyes (P<0.01). BF (µl/min) within the anterior ONH was significantly reduced in the EG eyes as compared to the control eyes measured at IOP 40 mmHg (Table, Col 2, P=0.001). The mean BF difference between the two eyes was -37±19%. Since RNFLT in the EG eyes became significantly thinned, the BF was also assessed in both eyes within a volume tissue starting from the ONH surface and 0.5 mm posteriorly; the result showed similar BF difference between EG and control eyes (Col 3, mean BF difference was -29±8%, P=0.01) to that measured within the anterior ONH (Col 2). In the posterior ONH, the BF in the EG eyes were 20-60% lower than the control eyes (Col 4, P=0.18) except for one eye (ID:139), which had unexpected higher BF than the control eye. Percentage change of post-laser RNFLT relative to the baseline of both eyes and the damaged area of optic nerve in EG are shown in Col 5 and 6, respectively.
Conclusions:
BF and regulatory deficit developed in both anterior and posterior ONH regions in EG. It suggests that BF measured in the superior ONH may be an indicator of BF change in deep tissue.
Keywords: optic nerve • blood supply • ischemia