PROLONGED INTRAOCULAR-PRESSURE REDUCTION FOLLOWING INTRAVITREAL BARIUM INJECTION IN RABBITS

The isolated ciliary epithelium contains barium-inhibitable potassium channels. The present study was aimed at testing the in vivo effects o f barium on aqueous humor dynamics in rabbits. BaCl2 was administered to one eye by topical delivery or intravitreal injection. Dynamic meas urements included intraocular pressure, outflow facility, episcleral v enous pressure and aqueous flow (fluorophotometry). Barium dynamics we re studied using Ba-133. Intraocular pressure was not altered after to pical administration of BaCl2. Ba-133 was not detected in the aqueous after delivery of eyedrops containing the radiochemical. Intraocular p ressure decreased following intravitreal injection of BaCl2 (0.15 mu g ). The onset of this pressure reduction was 12 to 16 hr, the maximum d ecrease (-11.3 mmHg) occurred at 2 days, and the effect persisted (-4. 2 mmHg) for approximately 12, days after the injection. Outflow facili ty and episcleral venous pressure were not altered. However, aqueous h umor flow 5 to 6 days after the injection was decreased by 42% to 63% as determined by fluorophotometry or calculated tonographic data. The injection was not associated with findings of intraocular inflammation , Radioactivity was detected in the vitreous within the first 3 days a fter the injection; however, activity was present in the ciliary body, equally distributed between the cell membrane and soluble fractions, seven days after the injection. Intravitreally injected BaCl2 results in a prolonged intraocular pressure decrease relating to reduced aqueo us formation. While the mechanism(s) for the BaCl2-induced decrease in pressure are not clear, possibilities include a Ba2+ interaction with ciliary epithelial K+ or N-type Ca2+ channels. (C) 1996 Academic Pres s Limited