24-hour Study of Dorzolamide/Timolol and Latanoprost/Timolol Fixed Combinations

Inclusion Criteria: * Consecutive primary open-angle (POAG) and exfoliative glaucoma (XFG) patients will be recruited. * Patients included will be older than 29 years * Have early to moderate POAG, or XFG (less than 12 mean deviation visual field loss attributed to glaucoma and 0.8 or better vertical cup-to-disc ratio) * Will be on therapy with latanoprost for more than 3 months; * Have at treated baseline IOP at 10:00 (two consecutive readings) greater than 21 mm Hg * Have a reliable visual field (at least two visual fields with less than 30% fixation losses, false positives or negatives) * Have a best corrected distance Snellen visual acuity \> 1/10 * Have corneal pachymetry within the 550 ± 55 μm range, understand the study instructions and are willing to attend all follow-up appointments * Are willing to comply with study medication usage * And have open, normal appearing angles Exclusion Criteria: * Patients will be excluded if they have: a risk for significant deterioration during the study * Known previous history of lack of adequate response (\< 10% reduction) to any topical glaucoma medication * Less than 20% daytime IOP reduction on latanoprost; * Systemic contraindications to topical beta-blockers (asthma, bradycardia, severe congestive heart disease) * Known contraindications to prostaglandins, history of ocular herpetic disease, or cystoid macular edema * History of trauma, inflammation, surgery or past use of steroids (within two months) * Severe dry eyes * Use of contact lenses * Signs of ocular infection, except blepharitis * Corneal abnormality that may affect IOP measurements * Unwillingness to accept the risk for hyperchromia of the iris or development of hypertrichosis * And females of childbearing potential or lactating mothers