Depth of Penetration of Scanning Laser Doppler Flowmetry in the Primate Optic Nerve

Abstract

Objectives: To estimate the measuring depth of the blood flow and to establish the vascular contributions to these measurements with scanning laser Doppler flowmetry (SLDF) of the primate anterior optic nerve.Methods: Optic nerve blood flow in each eye of 8 monkeys was measured using SLDF before and following surgical occlusion of the central retinal artery (n=4) or posterior ciliary arteries (n = 4). The regional blood flow in both eyes was determined using a nonradioactive microsphere method.Results: The blood flow in the nerve fiber layer (NFL), including the prelaminar region, was measured with microspheres after central retinal artery occlusion; it was significantly reduced (−83%) with no significant change in the combined laminar and retrolaminar regions. The blood flow measured with SLDF had a 51% reduction. After posterior ciliary artery occlusion, the blood flow in the NFL was measured with microspheres and was not significantly affected (+2%); neither was that measured with SLDF (−12%). However, there was a 51% reduc-tion in the laminar and retrolaminar regions when microspheres were used. The mean±SD tissue thickness of the NFL was 359±16 µm and 353±54 µm in each group.Conclusions: Scanning laser Doppler flowmetry measures blood flow principally in the NFL of the anterior optic nerve, which is primarily supplied by the central retinal artery. Blood flow in the laminar and retrolaminar regions makes a small contribution to the SLDF measurement, with an NFL thickness between 300 and 400 µm.Clinical Relevance: Scanning laser Doppler flowmetry is used for the noninvasive evaluation of ocular microcirculation in diseases such as glaucoma. Because of the dual blood flow supply in the optic nerve and the limited penetration power of the laser, the instrument primarily measures the microcirculation on the surface of the optic nerve, which is largely supplied by the central retinal artery rather than the ciliary arteries.

Noninvasive Monitoring of Murine Tumor Blood Flow During and After Photodynamic Therapy Provides Early Assessment of Therapeutic Efficacy

“…Laser Doppler can noninvasively monitor the flow change, but most systems measure only the tissue surface (penetration depth <500 Am; refs. 15,16). Pogue et al have invasively monitored flow changes during PDT with laser Doppler using fiber probes inserted into tumors (17).…”

Foveolar Choroidal Blood Flow in Idiopathic Macular Hole

“…A 10 · 10 pixel measurement frame of the HRF effectively measures an area of 100 lm in size using 10°scan. It was shown that the potential effective measuring depth into a tissue using scanning laser Doppler flowmetry is at 300 and 400 lm [13]. Thus, when targeted in the foveola, HRF measurement frame localizes within the foveal avascular zone and measures the blood flow in choriocapillaris [12,22].…”

“…SLDF uses the optic Doppler effect to measure the amount and velocity of moving red blood cells. The spatial resolution of the system is approximately 10 mm 2 [12] and the thickness of the imaged layer is approximately 400 lm [13].…”

Postmenopausal Hormone Therapy Increases Retinal Blood Flow and Protects the Retinal Nerve Fiber Layer

“…However, the SLDF technique has been reported to present a 0 offset reading. [82][83][84] This offset reading may account in a part for our SLDF flow measurements and may have masked potential significant increases in capillary blood velocity and flow in the postmenopausal woman who were HT users. The 0 offset problem also generates some uncertainty as to the accuracy of the SLDF findings as presented, since the numbers generated by the SLDF reflect both BF and imaging noise.…”