Reduction in intraocular pressure induced by colchicine and related compounds

The effects of various microtubule inhibitors on the intraocular pressure (IOP) of albino rabbits were investigated. The compounds produced a marked fall in the IOP which was more prolonged after intravitreal injection than after topical administration. Tolerance to this response developed although no cross tolerance between colchicine and vinblastine was apparent. The drugs produced no effect on the pupil diameters and fluorescein angiography revealed no leakage of dye from the vessels of the iris. Lumicolchicine and trimethylcolchicinic acid were without effect on the IOP. The iris-ciliary processes contained more [3H]colchicine after intravitreal injection than after topical administration, and most was associated with the ciliary processes, the site of formation of aqueous humour. Further colchicine and vinblastine were bound within the tubulin containing fraction of this tissue. We suggest that colchicine and related compounds reduce the IOP via mechanisms of microtubule disruption which may partially inhibit the formation of aqueous humour by the ciliary processes.