Cataract is a common eye disease. Surgery can restore the sight of most patients and can make the corrected visual acuity improve significantly after surgery, many of them can reach 0.8 or above, however, there are a small number of patients who still can’t see well after surgery, what is going on? According to the current clinical research, there are mainly the following reasons. 1, the situation of the operated eye itself: we often compare the eye to a camera, the crystal is like a lens, the retina is like a film, cataract surgery is just a replacement of a lens, if the other lens or film is not good, it will not produce a clear image. For example, white spots in the central area of the cornea and postoperative corneal edema affect the light entering the eye, which of course will not produce clear vision; and then there are retinal diseases in the fundus, especially macular diseases (such as macular hemorrhage, macular degeneration, etc.), which will greatly affect the vision after surgery. 2. Posterior cataract formation: There are many cataract patients whose vision recovers well after surgery, but after a few days, months or years, their vision gradually decreases again, which is caused by the formation of posterior cataract. In cataract surgery, the surgeon preserves the posterior capsule of the original lens in order not to destroy the normal physiological structure of the eye as well as to implant the IOL very well. However, due to unclean aspiration of the crystal cortex or crystal epithelium during cataract surgery and the stimulation of the surgery itself will promote the proliferation and differentiation of the crystal epithelium and migrate to the surface of the posterior capsule membrane to form cloudy material, thus causing the vision loss again after cataract surgery. However, there is no need to be anxious if this situation occurs, the treatment is very simple, the doctor just needs to open an incision in the center of the posterior capsule membrane with a laser. 3. Astigmatism of cornea: After cataract surgery, due to the incision, the curvature of cornea will be changed to a certain extent, so that it will cause astigmatism of cornea, which will also affect the improvement of post-operative vision. Generally speaking, 3 months after the surgery, when the incision heals and the corneal astigmatism is stabilized, the vision can be improved by wearing corrective glasses at this time. 4. The influence of the IOL itself: normal crystals have the adjustment function, so that people can see both distant targets and near objects, while the degree of the monofocal IOL is fixed, and it can only make people see most clearly within a certain distance, either far or near clearly. In order to give the patient a better ability to read up close, the doctor will often implant an IOL that is a bit higher than the measured prescription, thus affecting the patient’s ability to see far away. However, if the patient wants to restore his or her vision at a distance, he or she can get an optometric prescription. 5. Measurement error of IOL prescription: Before cataract surgery, the corneal curvature and the length of the eye axis of the operated eye need to be measured, and then the prescription of the IOL can be calculated with these results. These tests require the use of a corneal curvature meter and an A-type ultrasound instrument. If the ultrasound head indents the cornea during the measurement process, the length of the measured eye axis will be small, resulting in an inaccurate calculation of the IOL, which will affect postoperative vision. There are even some eyes where it is difficult to measure the prescription of the lens, such as silicone oil eyes, where the A ultrasound cannot measure the axis of the eye and therefore cannot calculate the prescription of the lens, and the doctor will usually estimate the prescription of the IOL based on the patient’s previous vision and the refractive status of the opposite eye, thus producing certain deviations. 6. Other surgical complications: Cataract surgery, especially ultrasound emulsification surgery, is a complex microsurgery, so some surgical complications, such as intraocular hemorrhage, elevated intraocular pressure, endophthalmitis, uveitis, macular cystoid edema, etc., will inevitably occur, which will also affect the recovery of vision after surgery. However, due to the continuous improvement of instruments and equipment and the maturity of surgeons’ surgical techniques, these complications are now rare. Even if they do occur, they can be recovered with appropriate medication. Therefore, if a cataract patient’s vision does not improve or does not improve much after surgery, do not be anxious. The correct approach is to go to the hospital for examination in time, ask the doctor to find out the cause of vision loss and take appropriate treatment measures actively.