请帮我分析一下下面这句话的语法结构,这是现代大学英语第三册第一课里面的一句话.
During the course I had come to realize that while my world was expanding and new options were opening for me,my father,who was in his sixties,was seeing his world shrink and his options narrow.
was seeing 后面的部分怎么理解，是宾语从句吗？