Human eye The upper end of the range is given in terms of normal visual performance as 10 cd/m (100,000,000 or one hundred million candelas per square meter). The eye includes a lens similar to lenses found in optical instruments such as cameras and the same physics principles can be applied. The pupil of the human eye is its aperture; the iris is the diaphragm that serves as the aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it
Sigurd Snake-in-the-Eye Sigurd Snake-in-the-Eye Sigurd Snake-in-the-eye (Old Norse: Sigurðr ormr í auga) was a Viking warrior in the middle of the 9th Century. He was supposedly one of the sons of the legendary Viking Ragnar Lothbrok. "Snake-in-the-eye" as part of Sigurd's name denoted a physical characteristic. He was born with a mark in his eye, described as the image of the Ouroboros (a snake biting its own tail). The snake mark had been prophesied by his mother Aslaug, the daughter of the Valkyrie Brynhildr. As a boy, Sigurd was close to his father and accompanied Ragnar on a hazardous expedition through Rus'