A Clinical Trial to Evaluate the Clinical Efficacy of Cyclosporine 0.1% (Ikervis®) for Moderate to Severe Dry Eye Patients. (IKE-03-SWITCHING)

Inclusion Criteria: 1. Age between 19 and less than 80 years old 2. A patient with moderate or severe dry eye who has used Cyclosporine 0.05% eye drop for more than 3 months and has no or insufficient treatment effect \- No or insufficient treatment effect should meet the following criteria through tests used to diagnose dry eyes * A SANDE (Symptom Assessment in Dry Eye) score of 40 or more on the severity and frequency of dry eye symptoms. * Cornea staining score (NEI scale) 3 or more points * Tear Break Up Time(TBUT) 10 seconds or less * Tear volume tested by Tear Meniscometry less than 5mm * Has One or more of the dry eye symptoms; stinging, irritating, itching or blurred vision. * Use of diquafosol tetrasodium 3% eye drop and/or artificial tears are allowed with no change of products and dosage throughout the trial period 3. A person who voluntarily agrees in writing to participate in this clinical trial Exclusion Criteria: 1. Use of eye drops within four weeks of the consent date such as steroids, glaucoma, allergies and anti-inflammatory drugs, etc. 2. Systematic steroid within four weeks of the consent date 3. Patients with pterygium 4. Start new immunosuppressive drugs or change in dosage that can affect immune function within four weeks of the consent date due to an unregulated systemic disease. 5. Severe MGD patient 6. Ophthalmic surgery (including Lasik/Lasek) and trauma in eyes within the last three months 7. Wearing contact lenses during a clinical trial period 8. Planning an eye surgery (including Lasik/Lasek) during the clinical trial period 9. Hypersensitivity to the clinical trial drug 10. Active or suspected eye infections 11. Pregnant or breastfeeding, or women planning to become pregnant 12. Participation in other clinical trials within three months 13. Any person who is deemed unfit for clinical trial by a investigator