IOL implantation during cataract surgery is generally necessary because the removal of one’s own existing lens must be replaced with something else. The lens is the equivalent of a prism in the eye and acts as a refractive lens. If the lens is missing its refractive action, light from the outside world to the eye cannot be gathered on the retina, and blurred vision occurs. For example, in the 1980s and 1990s, intracapsular extraction or extracapsular extraction was used without IOL implantation, when the eye was in a high refractive state and required a prism like the thickness of a beer bottle or so, which was worn on the eye to barely see clearly, converting it into an intraocular lens, which is a substitute for glasses implanted in the eye. There are special cases that do not require IOL implantation, such as high myopia patients, where the IOL may be implanted as little as 0 degrees or 1 degree, with or without an IOL. Because IOLs mainly play a refractive role, the refractive status is the same with or without IOL implantation after excluding high intraocular myopia combined with fundus pathology. In fact, IOL implantation is recommended for this type of patient because it maintains the relative stability of the intraocular structures or the stability of the anterior and posterior segregation.