The present invention relates to an ophthalmically acceptable vehicle, comprising: an aqueous suspension having a first viscosity, said suspension comprising from 0.1% to 6.5% by weight, based on the total weight of the suspension, of a carboxyl-containing polymer prepared by polymerizing one or more carboxyl-containing monoethylenically unsaturated monomers and less than 5% by weight of a cross-linking agent, said weight percentages of monomers being based on the total weight of monomers polymerized, said carboxyl-containing polymer having average particle size of not more than about 50 µm in equivalent spherical diameter, wherein the carboxy-containing polymer is polycarbophil, and a sufficient amount of a second polymer allowing said carboxyl-containing polymer to remain suspended, wherein upon contact with tear fluid, said vehicle gels to a second viscosity which is greater than the first viscosity, wherein the second polymer is a cationic chitosan and wherein said first viscosity of the aqueous suspension is in a range between 1,000 to about 30,000 cps as measured at room temperature of about 25 °C using a Brookfield Digital LVT Viscometer equipped with a number 25 spindle and a 13R small sample adapter at 12 rpm.
