OBJECTIVES: The presence of the preservative benzalkonium chloride (BAK) at 0.01% concentration in commercialized prostaglandin eye drops for glaucoma is known to increase the risk of ocular surface disease (OSD), which worsens with the extent of exposure to BAK. We aimed to estimate longer term clinical outcomes with travoprost preserved with Polyquad® 0.001% instead of BAK. METHODS: A Markov microsimulation model was developed (TreeAge) to assess the development of OSD and disease progression (Mean Defect [MD], in db) over 10 years, in patients initiating travoprost with Polyquad® followed by travoprost/beta-blocker fixed combination vs. the same sequence using BAK-preserved drops. Initial patient’s characteristics came from distributions on age (normal), sex, OSD presence, disease stage (uniform) and anticipated progression rates (triangular). The risk of developing OSD in aging population was derived from a US incidence study, multiplied by independent risk factors (age, sex, duration and amount of BAK-containing drops received). Rates of disease progression (db/year) came from landmark studies in OHT/glaucoma, multiplied by independent accelerating factors (disease stage, treatment line, OSD severity, non-compliance). Compliance was expected by experts to be 20% (absolute) better with Polyquad® vs. BAK-preserved drops. RESULTS: Using 3000 trials (mean age 57 years, 57% female, 14% with initial OSD, mean MD -4db), 47.6% [41.5-53.6%] of patients receiving in first and second line BAK-preserved travoprost treatments are expected to have OSD at 10 years versus 31.7% [28.5-35.1%] with Polyquad®. In OHT/early glaucoma patients, the model predicted the progression to advanced glaucoma (MD