Our eye is actually a complex optical system. The structure of the eye consists of two main systems, the refractive system and the photoreceptor system. The refractive system of the eye can be seen as a complex set of concentric co-axial lens combinations. You can think of it as an advanced camera, and the lens in the eye is the equivalent of one of the lenses. It is shaped like a biconvex lens, completely transparent, and has a high refractive power. A cloudy lens is called a cataract. Surgical removal of cataract means removing the patient’s original lens, which is like removing the lens of a camera, so you can imagine that a camera without a lens cannot take clear pictures. Therefore, it is necessary to implant an artificial lens in order to obtain the ideal refractive state after surgery, and finally, the patient can get a clear image on the retina. The IOL, like a spectacle lens, has a prescription, which is measured by an ultrasound examination of the patient’s eye before surgery. It is very important, if the measurement of the eye axis is 1mm off, the final result can be 3D off (300 degrees of glasses). Therefore, the patient is required to cooperate well with the examiner during the examination in order to minimize the error as much as possible. The appropriate IOL prescription is selected preoperatively based on each patient’s ultrasound findings, with the aim of giving the patient a refractive status close to orthokeratology after surgery. However, this is only theoretical, and the final refractive result is influenced by many factors and may not be exactly the same as expected before surgery, and there will be some refractive error. In addition, the astigmatism that the patient had before surgery cannot be corrected by this procedure. Therefore, after the refraction has stabilized for three months after surgery, the patient can undergo an optometric examination and decide whether glasses are needed based on the results. In addition, most of the currently implanted IOLs are monofocal and have no adjustment power. Therefore, patients cannot see as well as they did when they were young, both near and far. If the post-operative refraction is close to orthopia, then focal lenses are needed for near vision. If the postoperative refraction is low myopia, then it is possible that a pair of glasses will be needed for distance viewing. Of course, whether or not to get glasses after surgery is also related to the patient’s age, work needs, lifestyle, previous history of lens wear, and refractive status of the opposite eye.