AbstractIntracardiac injection of 15 μm microspheres labeled with85Sr (strontium) and141CE (cerium) were used to determine ocular blood flow in seven rabbits before and 25 min after bilateral application of tropicamide to the cornea. By using two different isotopes distinguishable under gammaspectrometry, each animal served as its own control. After administration of two drops of 1 % tropicamide, no significant difference in blood flow between treated and untreated eyes was observed.