Visualization of water movement in the living rabbit eye.

Water enriched with the stable isotope 17O (H2(17)O) shortens the transverse relaxation time (T2) of protons in water and can therefore be used as the contrast agent for proton magnetic resonance (MR) imaging. This agent can be given topically or intravenously to demonstrate water movement in the eye. Topical H2(17)O (0.05-0.1 ml/eye, 10% enrichment) entered the anterior chamber within 5 min and dissipated from the chamber in a single-exponential fashion (flow-rate constant k = 0.1 min-1), principally due to an exchange with the iridic circulation. No H2(17)O was detected in the vitreous. Intravenous administration of H2(17)O (1 ml/kg, 10% enrichment) resulted in rapid entry (less than 20 min) of the agent into the aqueous chamber. Again, no H2(17)O was detected in the vitreous. The lens region, on the other hand, showed an increase in image intensity with time that reached a plateau after 40 min. Although these findings are preliminary, acetazolamide (20 mg/kg injected intravenously) appeared to affect iridic circulation, possibly through vasoconstriction. Potential application of this H2(17)O-enhanced MR imaging technique is discussed.