Newer therapeutic vistas for antiglaucoma medicines

Glaucoma is second to cataract as a leading cause of global blindness and is the leading cause of irreversible visual loss. By the year 2020, almost 80 million people are estimated to be affected with open-angle glaucoma and angle-closure glaucoma. Sufficiently high concentrations of a free drug should be achieved within the aqueous humor and at the iris/ciliary body for sufficiently illustrating an antiglaucoma effect. Most drug groups including cholinergic agents, prostaglandin analogs, and carbonic anhydrase inhibitors being used in glaucoma were initially developed for other effects or routes and later found their use in the control of glaucoma. Hence, these molecules are not tailor made for delivery into the eye. Discovery of new molecules requires at least 15-20 years; hence, it may be concluded that instead of abandoning the existing molecules. It may be worthwhile to apply a novel drug-delivery approach to enhance ocular bioavailability and reduce systemic side effects of currently used agents. This review will elaborate on the potential to pharmaceutically tailor existing antiglaucoma agents using approaches including liposomes, collagen shields, dendrimers, in situ forming gels, and micro- and nanoparticles for achieving improved ocular effectiveness. Further to this, a preliminary discussion on miscellaneous agents such as siRNA, peptides, antioxidants and nitric oxide-releasing agents that are recently being proposed for the relief of glaucoma is also covered.