Bronze oral suction instruments have been unearthed that seem to have been used for this method of cataract extraction during the 2nd century AD.[28] Such a procedure was described by the 10th-century Persian physician Muhammad ibn Zakariya al-Razi, who attributed it to Antyllus, a 2nd-century Greek physician. The procedure "required a large incision in the eye, a hollow needle, and an assistant with an extraordinary lung capacity."[29] This suction procedure was also described by the Iraqi ophthalmologist Ammar ibn Ali of Mosul, in his Choice of Eye Diseases, also written in the 10th century.[29] He presented case histories of its use, claiming to have had success with it on a number of patients.[29] Extracting the lens has the benefit of removing the possibility of the lens migrating back into the field of vision.[30] A later variant of the cataract needle in 14th-century Egypt, reported by the oculist Al-Shadhili, used a screw to produce suction. It is not clear, however, how often this method was used as other writers, including Abu al-Qasim al-Zahrawi and Al-Shadhili, showed a lack of experience with this procedure or claimed it was ineffective.[29][verification needed]