The cornea of the normal human eye can be histologically divided into five layers, from the outer to the inner surface: corneal epithelium, anterior elastic layer, stroma, posterior elastic layer, and endothelium. Among them, the corneal stroma accounts for the largest proportion, about 90% of the entire thickness. The corneal stroma consists of about 200 layers of collagen fiber bundles arranged in thin sheets neatly. These collagen fiber bundles are characterized by high toughness and high resistance to tension, which are decisive factors in maintaining the toughness and tension of the cornea. Cone keratoconus is a corneal lesion characterized by dilatation of the cornea, causing the central part of the cornea to protrude forward, thin and conical and produce highly irregular astigmatism. The main clinical symptom is myopia in one or both eyes, and the degree of myopia and astigmatism increases progressively, which is difficult to correct by optical glasses. As the disease progresses further, corneal edema and scarring will appear in the late stage, which may lead to corneal perforation and blindness in severe cases. The cause of primary cone cornea is related to the progressive decrease in the amount of corneal collagen tissue or structural changes in collagen fibers, resulting in abnormal distribution and arrangement of collagen tissue. There is no good treatment for the disease in the past. After the diagnosis of cone keratoconus, the continuous dilatation of the cornea can be controlled by wearing rigid oxygen-permeable contact lenses (RGP) in the early stage, or by corneal stromal ring implantation to control the progression of the disease. In the advanced stages of the disease, the only other option is corneal transplantation. Currently, corneal donors are extremely scarce in China, and the price of surgery is high, leaving many patients with conical corneas to wait in a blurred world. Now, there is a new method to control the development of cone corneas – Corneal Cross Linking (CCL) treatment, which is undoubtedly a blessing for patients with cone corneas. The presence of collagen in normal human corneal tissue is a major factor in maintaining its tone, and the ratio and distribution of collagen and its spatial structure determine the biomechanical properties of the cornea. Corneal collagen cross-linking uses oxygen radicals generated by irradiating riboflavin with 370nm UV-A to create additional covalent bonds between amino acids adjacent to the collagen fibers in the corneal stroma, which can increase the biomechanical strength of the cornea and enhance its resistance to lysis, thus controlling the progression of dilated corneal diseases such as cone corneas; the oxygen radicals generated can also damage the DNA of pathogenic microorganisms and inhibit their growth and reproduction. It has a therapeutic effect on some infectious corneal diseases. Collagen crosslinking (CXL) is one of the most revolutionary new technologies in ophthalmology in the last decade or so. It first originated in Europe and was first reported by Spoerl and Seiler in 1997, and the clinical results of cone corneal treatment were reported in 2003. It has now been used for 20 years and has been widely used in clinical practice abroad for 10 years. The treatment is mainly applied to dilated keratoconus such as cone keratoconus, but also has good results for some severe infectious keratitis. Collagen cross-linking technology brings new hope for the treatment of many kinds of keratoconus and has been clinically observed to be reliable for many years. The most advanced instruments introduced by our hospital are the most advanced models in the world. The biggest advantage of this technique is that it is easy to operate, less painful for patients, less complications, and can effectively control the progression of cone keratoconus and shorten the course of infectious corneal diseases, increasing the cure rate. Indications for Corneal Cross Linking (CCL) treatment: 1) cone cornea; 2) refractory corneal ulcer; 3) corneal degeneration; 4) cone cornea after LASIK; 5) large vesicular keratopathy, etc. Safety of Corneal Cross Linking (CCL) treatment: The light wavelength of CCL treatment is 370 nm, the light passes through the corneal stroma and is rapidly attenuated and partially absorbed by riboflavin, only 7% of the light passes through the cornea and enters the eye, when the thickness of the cornea in the treatment area exceeds 400 microns, the light will not damage the endothelial cells and intraocular tissues in the deep layer of the cornea. When the thickness of the treated area exceeds 400 microns, the light does not damage the deep endothelium and intraocular tissue.