Reduction in pupil size
There is constriction of the pupil, which is medically known as meiosis due to the nerve pathway’s disruption. The cancerous cells from the tumor in the lungs resulting in the disruption of nerve signals towards the face, and the reduction in pupil size happens on one side of the eye in most cases. The two muscles that control the pupil size are the circumferential sphincter muscle cells, and they are present in the iris, and the cancer cells disrupt the activity of these sphincter muscles.