Definition
to be extremely busy or deeply involved in something
忙于某事，分身乏术
I've been up to my eyes in work lately, I really don't have time to go on vacation.
我最近忙于工作，真的没有时间去度假。
During the final exam week, the students are all up to their eyes in studying.
在期末考试周，学生们都忙于学习。
Since taking over this project, she has been up to her eyes in work every day.
自从接手这个项目以来，她每天都忙于工作。