Chronic Optic Neuropathy Causes Decreases in both Inner Retinal Blood Flow and Prelaminar Optic Nerve Blood Flow

Abstract

Purpose: Our purpose was to determine in a prospective, observational clinical study if optic neuropathy results in an obligatory decrease in blood flow to the inner retina and optic nerve due to decreased metabolic demand from non-functioning neurons. Visual stimulation causes transient hyperemia, but it is unknown if decreases in neuron activity cause reduced blood flow.

Methods: Laser speckle blood flowgraphy imaging (LSFG-NAVI; Softcare Ltd, Fukuoka, Japan) was performed on a 25x20 degree area of the fundus incorporating the optic nerve head. Blurring of the laser speckle pattern by moving particles in the image plane was used to simultaneously measure blood flow in the major circumpapillary retinal arteries and veins, and below the surface of the optic nerve head. Blood flow was determined in each eye of 19 patients with unilateral optic neuropathy (ischemic=13, compressive=5, inflammatory=1) in the chronic state. Inner retinal blood flow and optic nerve head blood flow were compared between affected and unaffected eyes. Retinal nerve fiber layer (RNFL) and retinal ganglion cell layer complex (GCL) were compared to retinal and optic nerve blood flow.

Results: There was a significant decrease in inner retinal blood flow (supplied by branches of the central retinal artery) in eyes with optic neuropathy compared to the fellow normal eye (P=0.002; mean=69±17% of fellow eye). A significant decrease in optic nerve head blood flow deep to the superficial retinal capillaries overlying the optic nerve was also present (P<0.001; mean=65±22% of fellow eye). There was also significant decrease in both RNFL (P=0.02; mean=83±32% of fellow eye) and GCL thickness (P<0.001; mean=71±11% of fellow eye), but no significant correlation between the inter-ocular asymmetry of retinal or optic nerve blood flow and RNFL or GCL thickness.

Conclusions: Chronic optic neuropathy results in decreased retinal and optic nerve head blood flow, likely due to reduced metabolic demand. Laser speckle blood flowgraphy allows non-invasive simultaneous measurement of retinal, choroidal, and optic nerve head blood flow, which may be proportional to metabolism and neurovascular coupling.