TransPRK is a type of keratomileusis and is a surface cutting procedure, TransPRK can be called “trans-epithelial laser keratomileusis”, its main feature is to use only one excimer laser to remove both the corneal epithelium and the anterior corneal stroma to complete the change of corneal morphology and achieve refractive correction. The main feature is that only one type of excimer laser is used to remove both the corneal epithelium and the anterior corneal stroma. The two main types of keratomileusis include surface and stromal cutting. Again, let’s go through a diagram to understand the concept of surface and stromal cutting. As we know, the cornea is divided into 5 layers, from anterior to posterior: corneal epithelium, anterior elastic layer, stroma, posterior elastic layer, and corneal endothelial cell layer. Among them, the thickness of the corneal stroma accounts for 90% of the total thickness of the cornea, the epithelial layer is also close to 10%, and the other layers are very thin. Surface cutting in keratoconus surgery means removing the corneal epithelium first, and then performing excimer laser cutting to change the curvature of the cornea to achieve refractive correction. The green arrow in the diagram shows the basal layer of the corneal epithelium. The laser will cut away the anterior elastic layer and continue to cut in the anterior corneal stroma. In stromal cutting, laser cutting is performed in the stromal layer of the cornea. The usual method is to create a corneal flap, which is the level indicated by the red arrow, and remove the anterior corneal epithelium, the anterior elastic layer and a portion of the anterior stroma, and then perform laser cutting on the remaining corneal surface to change the curvature of the cornea, which is most familiar as LASIK. Nowadays, many people know more about stromal cutting, and we often hear about femtosecond laser-type surgery, which is actually LASIK surgery with a femtosecond laser flap, and is currently the main surgical procedure for corneal stromal cutting. However, is LASIK the best surgery, is surface cutting meaningless? Of course not. Surface reduction is still a very important surgical option. The most basic procedure is the common PRK procedure, in which the corneal epithelium is removed with an epithelial scraper and the cornea is cut with an excimer laser. This classic surface cutting approach in the operating room is more painful for patients after surgery. The post-operative pain is related to the unsmoothness of the epithelial scraping surface, which is why the LASEK and EPI-LASIK surgical approaches were introduced. Both procedures involve creating an epithelial flap, which is a complete peeling off of the corneal epithelium, followed by excimer laser cutting, and finally covering the epithelial flap. In this way, the epithelial surface is smoother and the epithelial flap is repositioned, which can reduce the patient’s pain. The difference between the two procedures is that the method of creating the epithelial flap is different: LASEK involves soaking the corneal epithelium in alcohol and then peeling it off, while EPI-LASIK involves peeling the epithelial flap off with a blunt epithelial knife. This method of making the corneal epithelial flap actually still faces postoperative problems such as pain, slow recovery, and corneal clouding haze. TransPRK is another new attempt at surface cutting. Its basic feature is to finish the surgery with excimer laser only, that is, first burn off the corneal epithelium with excimer laser, and then continue to finish the cutting of the anterior stromal layer of the cornea with excimer laser to correct the refractive error. Once you hear this concept, you will think that the idea is very simple, so why not directly cut with excimer laser before but to scrape off the epithelium or remove the epithelium with alcohol or epithelial knife? In fact, the main reason for this problem is that with the previous excimer devices, the laser frequency was relatively low and if the epithelium was burned off with the excimer laser, it would take longer. Now, with the high frequency excimer laser, such a procedure is possible. Some people call the TransPRK procedure A One-Step Procedure With No-Touch, which basically sums up the main features of this procedure.