The lens is located between the iris and the vitreous humor. The outermost layer is protected by a capsule membrane that allows only small molecular weight substances to pass through, and the inner layer has lens epithelial cells, and further in there are neatly arranged lens fibers and other tissues surrounded by atrial water to provide nutrients in order to keep the lens clear. So the lens is cloudy and the cause of cataracts must be related to the abnormalities of these tissues. In other words: damage to the lens capsule membrane, change in the permeability of the lens capsule membrane, and abnormal atrial water lens cell metabolism disorder lens protein degeneration will cause lens clouding.
However, scientific research is always difficult. At present, scholars at home and abroad still only know that cataracts may be related to ageing, heredity, metabolic abnormalities, ultraviolet over-exposure, traumatic radiation poisoning, local nutritional disorders, and certain diseases in the eye. But how exactly do these factors cause cataracts? Which factor initiates the disease process and which is the dominant factor? What is the exact pathogenesis? These questions are still not fully understood.