1.The classification of IOLs is based on the position of placement: anterior chamber fixed IOLs, iris fixed IOLs, and posterior chamber fixed IOLs. Usually, the best placement position for IOLs is within the capsule of the natural lens, which is the position of the posterior chamber fixed IOL, where the IOL can be better positioned, without friction with the surrounding tissues and with less inflammation. However, in some special cases, the ophthalmologist may place the IOL in other positions, for example, for patients with corrected refractive error, the natural lens may be preserved and a crystalline intraocular lens (PIOL) may be implanted; or for patients with complications such as rupture of the capsular bag during surgery, an anterior chamber IOL or a posterior chamber IOL may be implanted with suture fixation. 2. Classified according to the size of the surgical incision: Hard IOL: Generally hard and inelastic in texture, with a diameter of 5.5-6 mm, then a 6 mm surgical incision is needed to implant it into the eye, with a relatively large incision and heavy postoperative reaction. Foldable IOL: With the development and popularization of ultrasound emulsification surgery, in order to implant the IOL since a very small incision, people designed and manufactured a crystal that can be folded or curled in 1984, which has been applied and continuously improved in the last decade. 3.Classification according to function: Multifocal IOL: Multifocal IOLs are divided into two types: refractive type and diffractive type. (1) The concept of refractive type is relatively simple, mostly biconvex lenses with 3-5 refractive areas of different diopters on the front surface, with different areas responsible for distant or near-focus imaging, and the imaging depends on the size of the pupil, and the imaging quality is greatly affected by the size of the pupil and the deviation of the artificial lens. Representatives of this type of crystals such as AMO’s ReZoom. (2) Diffractive type of optical surfaces take a step progressive diffraction technique, presenting a stepped design in 12 concentric circles with a height between 0.3-1.2 microns and a decreasing step width with the same regularity, while the peripheral area is the refractive zone. The stepped progressive diffraction structure blends with the peripheral refractive zone, allowing the distribution of light energy to gradually favor the distant focus as the pupil increases. As a result of the redistribution of light energy, a decrease in visual quality and the occurrence of visual disturbances (glare, halos) are inevitable. A representative of this type of crystal is Alcon’s ReSTOR.