A clouding of the lens in the eye is medically known as a cataract. The human eye is like a camera, and the lens is like the lens of the camera, while the retina at the bottom of the eye is equivalent to the film. Cataract is like the lens of a camera becoming cloudy, so it is difficult for light to reach the retina, which is the “film”, and you cannot get a good image. Cataract is the leading cause of blindness in China, and is a common disease in ophthalmology, especially in the elderly. China is a region with a high prevalence of cataracts, with about 5 million cataract patients, increasing by 400,000-500,000 each year. However, many cataract patients are waiting for their cataracts to “mature” before surgery because of the traditional concept, which not only delays the surgery, but also seriously affects the quality of life. So when is the best time to have surgery for senile cataract? This question needs to be considered according to the patient’s comprehensive situation, such as the degree of lens clouding, visual acuity, the patient’s general condition, and the patient’s working requirements for visual acuity. In the past, surgery for senile cataracts was only done when the lens was completely clouded and the vision was below 0.1. Especially for the cataract intracapsular extraction in the past, the best time for surgery was only after the lens was completely clouded. With the continuous progress of science and technology, cataract surgery methods have made a qualitative leap. Currently, the best surgical procedure for cataract surgery with the least damage and the fastest recovery is the small incision ultrasound emulsification technique combined with folding IOL implantation. The common cortical age-related cataract is generally divided into four clinical stages: the initial stage, the expansion stage, the maturation stage, and the overmaturation stage. The lens in each stage can have different changes, and the doctor can accurately determine the state of the lens and the degree of lesion through some advanced instruments. The distended and pre-mature stages are the best time for ultrasound emulsification surgery. Therefore, it is not necessary to wait until the lens is completely cloudy before surgery is performed. Generally speaking, surgery can be considered when the patient feels difficulty in working and living, has difficulty in reading, has visual acuity below 0.5, and cannot be corrected with lenses. With the emergence of multifocal lenses and adjustable IOLs, surgery can be performed for those whose work nature requires high vision or who have difficulties in taking care of themselves (such as accountants, computer operators, drivers, etc.), even if the cataract is not mature and the visual acuity is around 0.6. Especially for patients with cataracts in the distended stage of hyperopia (short eye axis), if the crystal distension causes the anterior chamber to be too shallow, early surgery can not only improve the refractive state but also effectively avoid glaucoma attacks. If the surgery is performed too late, waiting until the mature stage, the nucleus of the lens becomes hard, the ultrasound energy required for surgery is larger, and the surgical damage and postoperative reaction will be aggravated. Therefore, it is not better to operate on senile cataracts as late as possible. The proper timing of surgery should be chosen based on scientific examination and personal life needs.