P 120 Determination of the tear volume as a method of assessing the precorneal residence time of various polymer formulations in rabbits

Purnose The incorporation of polymers into artificial tears both increases the thickness of the precorneal tear film and decreases the rate of drainaae of the for8nulations. On the basis of these effects, we hypothesized that a time study of the artificial increase in tear volume induced by such formulations could be a useful method of assessing their precorneal residence time. Methods New Zealand albino rrlbbits were used. The tear volume was measured under general anesthesia by determining the dilution ratio of a topically applied 1% fluorescein solution. The formulations studied were proprietary preparations of 1.4% PVA (Liquifilm, Allergan), 1% MC (Nlethylcellulose 1%. MSD-Chibret), 0.2% Carbomer 940 (Lacrinorm, Laboratoire CHAUVIN) and a 0.52% aqueous solution of HEC (Hydroxyethylcellulose). One drop (25~1) of the test formulation was instilled into one eye at different times before the determination of tear volume. A control group received a polymer-free aqueous solution. &&@ All the polymer formulations induced an increase in the tear volume as compared with the polymer-free solution. After administration of PVA, MC, HEC and Carbomer 940 preparations, the tear volume remained significantly increased for 5 min., 20 min., 20 min. and 60 min. respectively. Conclusions The precorneal residence times of these polymer formulations have been demonstrated to be shorter in humans than those observed in this study in rabbits. However. there is a similar rank order in the two species. Thus, the determination of the tear volume in rabbits providtzs a useful method for preliminary screening of new polymer artificial tears.