The present invention relates to a process for manufacturing an ophthalmic formulation of a carbonic anhydrase inhibitor, hydroxyl ethyl cellulose (HEC), and a beta-adrenergic antagonist for use in the treatment of ocular hypertension and glaucoma wherein the ophthalmic pharmaceutical formulation is devoid of benzalkonium chloride or any other preservatives. The present process for manufacturing is simpler, cost effective process to prepare the pharmaceutical ophthalmic formulation in a single tank, without the use of additional tanks that can be sterile filtered.