- Subjects will be recruited from the glaucoma practices at Johns Hopkins Hospital and Wilmer at Greenspring Station. Eligibility (see 5 below) will be assessed during their regularly scheduled visit. Participants will sign consent forms and will be scheduled for 3 study visits, none of which will be part of routine clinical care. The subject will be instructed NOT to use his/her prostaglandin eye drop on the day preceding study visit 1.