The lens of the human eye is like a transparent biconvex lens through which light rays converge on the retina. When the lens is cloudy, the transmission of light is affected and the vision becomes unclear. Cataracts are classified as developmental, senile, concurrent, traumatic, toxic, metabolic disorders, corticosteroid and posterior cataracts depending on their causes. Developmental cataracts, also known as congenital cataracts, are both endogenous and exogenous. Endogenous causes are related to fetal developmental disorders and are hereditary; exogenous causes refer to damage to the lens caused by maternal or fetal systemic pathologies, such as viral infections such as rubella, measles, chickenpox, mumps, hypoparathyroidism, malnutrition and vitamin deficiency in the first six months of pregnancy, all of which may cause it. The main factors in the formation of senile cataracts are the degeneration of proteins, the increase of insoluble proteins, sodium and calcium, the decrease of potassium and vitamin C and the deficiency of glutathione. Water-soluble albumin can be converted into insoluble protein, and the older the person is, the more insoluble protein there is. In addition, vitamin C deficiency, changes in crystal pH and the infiltration of toxic substances into the crystal can cause degeneration of crystal protein and produce cloudiness. For the elderly, oxidative damage to the crystal is the initial factor in cataract formation. Risk factors for cataract formation include excessive alcohol consumption, excessive smoking, excessive childbirth in women and certain systemic diseases, etc. However, the causes of age-related cataract formation are still not fully understood and need to be further studied. Complicated cataract is caused by certain eye diseases themselves, such as iridocyclitis, chorioretinitis, retinal detachment, retinitis pigmentosa, glaucoma, high myopia, septic corneal ulcer, old eye trauma and other eye diseases can cause complicated cataract. Traumatic cataracts include mechanical, radiation, and electric shock. Metabolic disorders cataracts are mostly seen clinically as diabetic cataracts. Corticosteroid cataracts are caused by long-term heavy use of corticosteroids locally in the eye or systemically. Posterior cataract is the clouding of the residual cortex and capsule after extracapsular extraction or linear extraction of cataract.