Validation of scanning laser Doppler flowmetry for retinal blood flow measurements in animal models

PURPOSE: To evaluate the validity of scanning laser Doppler flowmetry in retinal blood flow measurement in vivo using rabbit and monkey eyes and the microsphere technique. METHODS: A commercially available scanning laser Doppler flowmeter (SLDF), pigmented rabbits and cynomolgus monkeys were used. In rabbits, SLDF measurements at a retinal field approximately one papillary diameter away from the optic nerve head where discrete retinal vessels were not visible (vascularized medullary field) were compared with those at a field approximately one papillary diameter below the ONH (nonvascularized extramedullary field). The effect of intraocular pressure (IOP) on SLDF measurements was studied by elevating the IOP manometrically in both rabbit and monkey eyes. Retinal and choroidal blood flow measurements using the microsphere technique and an SLDF measurements were performed simultaneously in the same rabbit eye before and 30 min after 0.3 mg/kg intravenous injection of lomerizine, a calcium antagonist, or intravitreal injection of 20 microl of 10(-6) M endothelin-1. RESULTS: The blood flow measurement with an SLDF (SLDF flow) obtained from the medullary field in rabbits were 304 +/- 63 in an arbitrary unit (n = 24), while 392 +/- 39 in the extramedullary field. SLDF flow did not significantly changed by changes in IOP when it was below 50 mmHg, significantly decreasing with IOP elevation above that level in rabbits and a similar tendency was also seen in monkeys. It showed a significant correlation with retinal blood flow measured by the microsphere technique (r = 0.596, P < 0.0001) in rabbits; no correlation was found with the choroidal blood flow rate (r = 0.021, P > 0.1). CONCLUSIONS: SLDF measurements is thought to mainly reflect retinal circulation in rabbits and monkeys.