Studies have shown that ocular surface disease (OSD) is common among patients with glaucoma with a prevalence of 50% or more. The percentage of affected patients appears to increase with increasing number of topical anti-glaucoma products instilled. Both pre-clinical and clinical work has indicated that the preservatives used in anti-glaucoma drops, particularly benzalkonium chloride, are mainly responsible for this detrimental effect. As such more and more anti-glaucoma drugs without preservatives entered the market.