The prevalence of eye diseases in the desert and tropical countries led to the study of the eye by Arab doctors. Surgical treatment of the eye led to renewed interest in the structure of the eye. This was to give the Arab physicians the first real understanding of dioptrics, the part of optics dealing with the passage of light through transparent bodies like a lens or glass. This also laid the foundation of modem optics. The lens of the eye was to point the way to the use of crystal or glass lenses for magnification and reading, particularly by the old. The 'Optical Thesaurus' of Ibn al-Haitham (about 1038 A.D.) was the first serious scientific treatment of the subject.