unaided eye

详细解释:肉眼

例句：

An optical instrument that uses a lens or a combination of lenses to produce magnified images of small objects, especially of objects too small to be seen by the unaided eye.显微镜用一个透镜或一些透镜的组合来制造小物体的放大形像的视力工具，通常用来观察肉眼看不到的物体