This clinical trial is focused on studying the treatment of acquired blepharoptosis, a condition where the upper eyelid droops over the eye, potentially affecting vision. The treatment being tested is an eye drop solution called STN1013800, which contains the active ingredient oxymetazoline hydrochloride. This medication is designed to be used twice daily to help lift the eyelid and improve vision.

The purpose of the study is to evaluate how effective and safe STN1013800 is in treating acquired blepharoptosis. Participants in the study will be randomly assigned to receive either the eye drops containing oxymetazoline hydrochloride or a placebo, which looks like the real medication but does not contain the active ingredient. The study will last for a period of 42 days, during which participants will use the eye drops and attend regular check-ups to monitor their progress.

Throughout the study, the main focus will be on measuring changes in the position of the eyelid and assessing any improvements in vision. The study aims to determine if the eye drops can effectively lift the eyelid and improve the quality of life for those with acquired blepharoptosis. Participants will be closely monitored for any side effects or changes in their condition to ensure the treatment is safe and beneficial.