the naked eye
Normal vision that has not been enhanced or augmented in any way. Because bacteria are invisible to the naked eye, it was only relatively recently in human history that we even became aware of their existence. The fine print is so tiny, you can barely make it out with the naked eye.
*naked eye
the human eye, unassisted by optics, such as a telescope, microscope, or spectacles. (*Typically: appear to ~; look to ~; see with ~; visible to~.) I can't see the bird's markings with the naked eye. The scientist could see nothing in the liquid with the naked eye, but with the aid of a microscope, she identified the bacteria. That's how it appears to the naked eye.
naked eye
Sight unassisted by an instrument such as a microscope or telescope. For example, These insects are too small to be seen with the naked eye. This expression was first recorded in 1664.