Hypothesis: Changing to Travatan Z therapy increases the tear film break up time of subjects on Xalatan therapy presenting with ocular surface disease.

Patients who have been taking Xalatan monotherapy to treat their glaucoma and presenting with ocular surface disease will be advised to switch their medication to Travatan Z. Test results will be recorded at the day that the medication was changed and at follow-up to determine if there is a measurable change in tear film break up, corneal staining and in the Ocular Surface Disease Index.

Inclusion Criteria:

• on Xalatan monotherapy from 1 to 18 months
• 18 years of age or older
• has been diagnosed with ocular surface disease

Exclusion Criteria:

• special populations such as children, pregnant females, prisoners, etc.

patients will be selected from the ophthalmology clinic of the principal investigator