Various causes such as aging, trauma, poisoning, heredity, radiation, immunity and metabolic abnormalities can cause disorders of lens metabolism, resulting in clouding of lens proteins due to denaturation, leading to cataract. The classification by etiology is as follows: 1. Congenital cataracts: about 1/3 of cases have genetic factors. Cataracts caused by non-genetic factors are mainly clouding of the lens caused by malnutrition or infection during embryonic development, such as intrauterine rubella virus infection in the fetus during pregnancy. 2, age-related cataract: the most common, mostly seen in middle-aged and elderly people over 50 years old, increasing with age, mostly related to physiological aging, malnutrition, vascular sclerosis, long-term ultraviolet radiation damage, and endocrine disorders. 3.Complicated cataract: It refers to cataract complicated by other eye diseases, such as uveitis and retinal detachment. 4.Metabolic cataract: such as cataract caused by diabetes. 5.Traumatic cataract: It is caused by eye trauma. 6.Radioactive cataract: caused by X-rays, β and γ-rays radiation. 7.Drug and toxic cataract: such as cataract caused by chlorpromazine and trinitrotoluene. Therefore, there are various causes of cataracts.