因为 dress 当及物动词用时 宾语 必须是人
本句 是过去分词 作状语 与主语 是被动关系 故用过去分词
=after he was dressed in his doctor's uniform,he went in to see her.
如果用动名词 作介词宾语
应该是after being dressed in his doctor's uniform,he went in to see her.
或者是after dressing himself in his doctor's uniform,he went in to see her.
当然也可以 去掉after
用现在分词 作状语dressing himself in his doctor's uniform,he went in to see her.
如果强调动作在先 也可用现在分词的完成时
having dressed himself in his doctor's uniform,he went in to see her.
不过本句 是相继发生 最好不用现在分词的完成时
综上 用过去分词 作状语 最简练