This document discusses the anatomy and physiology of the lens and various types and causes of cataract formation. It describes the normal lens size, shape, position and refractive properties. It then covers abnormalities in lens shape, size and position. Various classifications of cataract are presented, including congenital/developmental cataracts, cataracts associated with ocular diseases, cataracts associated with systemic diseases, and cataracts due to other causes such as trauma or radiation. Objectives and suggested reading topics on cataract are also listed.