with the naked eye 用肉眼；凭肉眼；用肉眼看

【例句】
Results shallow red coral growth and growth pattern was more obvious with the naked eye can be observed.
浅海红珊瑚的生长结和生长纹比较明显，用肉眼就可以观察到。

Unfortunately, with the naked eye it's hard to see exactly what makes them messy.
不幸的是，肉眼很难看出到底是什么搅乱了它们。