According to the Ancient Greeks, vision was thought to a visual spirit emanating from the eyes that allowed an object to be perceived. The 11th century Iraqi scientist Ibn al-Haytham, also known as Al-hazen in Latin, developed a radically new concept of human vision. Ibn al-Haytham took a straightforward approach towards vision by explaining that the eye was an optical instrument. The description on the anatomy of the eye led him to form the basis for his theory of image formation, which is explained through the refraction of light rays passing between 2 media of different densities. Ibn al-Haytham developed this new theory on vision from experimental investigations. In the 12th century, his "Book of Optics" was translated into Latin and continued to be studied both in the Islamic world and in Europe until the 17th century.