This study is being conducted to evaluate the safety, tolerability, and pharmacokinetics of RCI001 eye drops 0.25% in healthy adult male participants. Pharmacokinetics means how the study drug is absorbed, distributed, and eliminated from the body over time.

Participants who meet the study requirements will be randomly assigned to receive either RCI001 eye drops 0.25% or placebo eye drops. The study treatment will be administered to the left eye according to the assigned dosing schedule. The study includes single-dose administration schedules and multiple-dose administration schedules for up to 15 days.

The study will monitor safety and tolerability through adverse event assessments, vital signs, physical examinations, electrocardiograms, laboratory tests, eye symptom assessments, and ophthalmic examinations. Blood samples will be collected at scheduled time points to measure the concentration of RCI001 in the blood.

Approximately 40 healthy adult male participants are planned to take part in this study.

Inclusion Criteria:

1. Healthy adult male volunteers aged 19 to 50 years at screening.
2. Body weight of 50.0 kg to 90.0 kg and body mass index (BMI) of 18.5 kg/m2 to 29.9 kg/m2 at screening.
3. Participants who have received sufficient explanation about the study, fully understand the study, voluntarily decide to participate, and provide written informed consent to comply with study requirements.
4. Participants who are considered eligible for this study by the investigator based on physical examination, clinical laboratory tests, medical interview, and other screening assessments.

Exclusion Criteria:

1. Participants with a current or past history of clinically significant disease in the hepatobiliary system, kidney, nervous system, immune system, respiratory system, gastrointestinal system, endocrine system, hematologic or oncologic system, cardiovascular system, urinary system, or psychiatric system, including but not limited to severe hepatic impairment, viral hepatitis, severe renal impairment, heart failure, Torsade de pointes, mood disorder, or obsessive-compulsive disorder.
2. Participation in another clinical trial, including a bioequivalence study, and administration of an investigational product within 6 months before the first planned administration of the investigational product.
3. Current smoker who cannot stop smoking during the study period. Participants who stopped smoking at least 3 months before the first planned administration of the investigational product may be eligible.
4. Consumption of grapefruit, grapefruit juice, or grapefruit-containing foods from 3 days before the first planned administration of the investigational product until the end of the study, or inability to abstain from grapefruit-containing foods and beverages during this period.
5. Participants who are considered unsuitable for participation in the study by the investigator for any other reason.

Individual participant data will not be made available to other researchers. The study has been completed and the results are planned to be submitted for publication. De-identified individual participant-level data are not planned for external sharing due to participant confidentiality, informed consent, regulatory, legal, and proprietary considerations related to the investigational drug product. Aggregate results may be disclosed through ClinicalTrials.gov, scientific publication, and/or regulatory submissions, as applicable.

Participants, investigators, care providers, and outcome assessors will remain masked to treatment assignment until the study is completed and the database is locked, except when unmasking is required for participant safety.