حنين بن إسحاق
Medieval Islamic Arabic and Persian scientists (unlike their classical predecessors) considered it normal to combine theory and practice, including the crafting of precise instruments, and therefore, found it natural to combine the study of the eye with the practical application of that knowledge. Hunayn ibn Ishaq, and others beginning with the medieval Arabic period, taught that the crystalline lens is in the exact center of the eye. This idea was propagated until the end of the 1500s.