In patients with Glaucoma, Xalost S or Xalatan or Taflotan-S are administered for 12 weeks. After 12 weeks, among them, Xalatan administration group are switched to Xalost S or Taflotan-S. Extension study period is 8 weeks.

To compare effect (ocular surface damage) and safety of preservative-free Latanoprost/Tafluprost to Benzalkonium chloride-preserved Latanoprost in primary open angle glaucoma or normal tension glaucoma.

Inclusion Criteria:

• Male or female diagnosed with glaucoma, age 19 or over
• Written informed consent to participate in the trial

Exclusion Criteria:

• Patients who have received or have plans lacrimal puntual occulsion
• Use of contact lenses
• Any other Glaucoma except primary open angle glaucoma/normal tension glaucoma (ex) Closed anterior chamber angle/ angle-closure Glaucoma)
• Any condition limiting patient's ability to participate in the trial