The visual phenomenon of seeing circles, diffraction lines, or light patterns when squinting at a bright light source is a well-known consequence of light interacting with the tear film, eyelashes, and eyelids of the human eye, and requires no citation.
The claim describes a familiar, everyday physiological optical observation regarding how the eye's structures and tear film diffract light when squinting. Under the instructions, trivially true observations of everyday optics are classified as common knowledge, requiring no formal citations from the retrieved literature.