Cataract (Cataract) is a disease that occurs in the lens inside the eye. Any clouding of the lens can be called a cataract, but when the clouding of the lens is mild, it does not significantly affect vision and is not noticed or ignored and is not included in the cataract category. According to surveys, cataracts are the most common cause of blindness and visual disability, with approximately 25% of the human population suffering from cataracts. Symptoms Bilateral, but the onset of the disease may be sequential in both eyes. Progressive loss of vision, sometimes with a fixed black spot visible against a bright background. Due to changes in refractive power in different parts of the lens, there may be hyperopia, monocularity, diplopia, and increased myopia. Clinically, senile cataracts are classified into three types: cortical, nuclear and subcapsular. Pathology 1. Cortical cataract (cortical cataract) is mainly characterized by gray-white clouding of the crystal cortex, and its development process can be divided into four stages: incipient, immature, mature, and overmaturity. 2. Nuclear cataract: The clouding of the crystal starts from the embryonic nucleus and gradually expands to the adult nucleus. The density of the nucleus increases, the refractive index increases, and the patient often complains of reduced presbyopia or increased myopia. In the early stage, the peripheral cortex is still transparent, therefore, the pupil is dilated in the dark to improve vision, while the pupil is narrowed in bright light to reduce vision. Therefore, surgery is usually performed without waiting for complete cortical opacification. 3. Posterior subcapsular cataract: Because the clouding is located in the visual axis area, it affects vision at an early stage.