Tafluprost Preservative Free Switch Study

Inclusion Criteria: 1. Age of 21 years or older and those who can provide informed consent. 2. Patients who have corneal disorders due to the prostaglandin usage. (At least one eye must have a score above 1 on the NEI scale) 3. Intraocular pressure (IOP) ≤ 21 mm Hg in the study eye at the screening examination (under treatment) 4. If only one eye is eligible, it is to be evaluated. If both eyes are eligible, then the eye with a higher NEI score will be selected for evaluation. 5. Pretreatment must be monotherapy with any of the following preserved ophthalmic solutions; latanoprost, travoprost, bimatoprost or tafluprost and its period must be longer than 3 months. 6. Outpatients who can visit the clinic on the designated day as instructed by the physician. 7. A best-corrected ETDRS visual acuity score of +0.6 logMAR (Snellen equivalent of 20 ⁄ 80) or better in each eye. Exclusion Criteria: 1. Those with severe visual field disorder (Mean deviation of 15 dB or worse) 2. Those with a history of ocular surgeries (such as corneal refractive surgery, intraocular surgery including ocular laser treatment which may affect the patient's ocular surface condition) within 6 months prior to the study initiation. 3. Those with severe dry eye (those in need of drug to treat dry eye), ocular allergy, ocular infection or ocular inflammation 4. Those who need to use systemic or ophthalmic steroids (excluding topical skin steroidal ointment) and anti-glaucoma agents other than latanoprost, travoprost, bimatoprost or preservative free tafluprost ophthalmic solution 5. Female patients who are pregnant, nursing or lactating 6. Those with a history of drug allergy (hypersensitivity) to the drugs to be used during the study period (anesthetic ophthalmic solution, fluorescein, etc.) or similar drugs to the investigational product 7. Those who need to wear contact lenses during the study period 8. Any corneal abnormality or other condition preventing reliable applanation tonometry 9. Anterior chamber angle less than grade 2 according to Schaffer classification as measured by Gonioscopy 10. Any uncontrolled systemic disease (e.g. hypertension, diabetes)