In recent years, foreign researchers have discovered that by means of UV riboflavin-induced cross-linking, the mechanical strength of the corneal stroma can be increased to stop the pathological process of conical cornea, which is promising to become a non-surgical treatment for conical cornea. The discovery of this technically significant breakthrough was actually highly serendipitous. Inspired by the discovery that the thickening and stiffening of collagen fibers that occurs in the aging process of the cornea has been shown to be related to the glycosylation of collagen molecules that occurs with age, in studies of the conical cornea, researchers have been attempting to enhance the strength of the stromal collagen fibers through hydroxyl radical-mediated oxidative reactions by using either light or heat-treatment of the cornea since the 1990s. Another clinically significant phenomenon is that conical corneas never occur in young diabetic patients, and even in the rare cases where conical corneas appear before the onset of diabetes, the disease no longer progresses due to the presence of diabetes precisely because diabetes causes a spontaneous glycosylation reaction within the corneal stroma, which strengthens the cornea. Based on these clinical findings, a team of German researchers first began the project in the late 20th century. It was found that the biomechanical properties of the cornea depend on the composition of the collagen fibers, collagen bundles and their spatial structure. The mechanical strength of the cornea in patients with conical corneas is usually half the normal value. The basic principle of cross-linking therapy is that the photosensitizer riboflavin (i.e., vitamin B2) is excited to the trilinear state under the action of ultraviolet light at a wavelength of 370 nm, generating a reactive oxygen family dominated by oxygen in the monolinear state. Reactive oxygen species can react with various molecules to induce chemical cross-linking reaction (type II photochemical reaction) between the amino groups of collagen fibers, thereby increasing the mechanical strength of collagen fibers and resistance to corneal expansion, 370nm is the peak absorption wavelength of riboflavin. Thus, this new treatment was born. According to a clinical study conducted in Germany, 22 cases of 23 eyes with severe cone cornea crosslinking treatment, follow-up after treatment for 3 months to 4 years, found that all over the treatment of cone cornea have stopped further development, 16 eyes (70%) corneal refractive power decreased by 2D, refractive error decreased by 1.14D. So the treatment of the eye did not appear in the cornea and lens transparency changes in the cornea and intraocular pressure did not show significant changes in endothelial density and corneal endothelial cell density. Neither corneal nor lens transparency changes, corneal endothelial cell density nor intraocular pressure showed significant changes, and 15 eyes (65%) gained a mild improvement in visual acuity, with a mean improvement of 1.26 lines. In 2004, a clinical study was conducted on 10 patients with progressive conical corneas in both eyes using UV riboflavin cross-linking treatment, in which one eye was used as the subject of cross-linking treatment while the other eye was used as the control, and soft corneal contact lenses were worn after the treatment. At 1, 2, 3, and 6 months postoperatively, demonstrated-corrected visual acuity, best-corrected visual acuity, and corneal topography were performed on both the treated and control eyes, and the results showed an average improvement of 3.6 lines in naked-eye visual acuity and 1.66 lines in best-corrected visual acuity, and the corneal topography showed an improvement in the symmetry of the corneal surface, a decrease in coma, and no significant changes in endothelial cell counts or intraocular pressure. Furthermore, in addition to its use in the treatment of conical corneas, this photorefractory cross-linking therapy can also be applied in the prophylactic treatment of medically induced corneal dilatation or in the postoperative treatment of corneal dilatation such as that induced by excimer laser in situ keratomileusis. In addition, this treatment can also be used for the treatment of corneal lysis lesions or superficial corneal ulcers. Studies have confirmed that cross-linking treatment can significantly improve the cornea’s resistance to a variety of degradative enzymes, but first need to test the remaining corneal thickness, and only when greater than 400um should be considered for this treatment, because suction sufficient corneal stromal thickness to ensure that the corneal endothelial cells have the process of treatment is not damaged.