Keratoconus is an unexplained corneal degeneration that manifests as progressive thinning of the center or a certain part of the cornea that bulges forward in the shape of a cone, resulting in varying degrees of visual dysfunction due to irregular corneal astigmatism and high myopia, and usually difficult to get good correction of visual acuity. Conical cornea is most common in adolescents aged 10 to 25 years old, and is one of the common diseases leading to severe low vision in adolescents. The course of the disease is slow, with 90% of the cases occurring in both eyes successively, and the extent of the lesions in both eyes is not consistent. The degree of myopia and irregular astigmatism is caused by the cone-shaped expansion of the cornea, which is gradually aggravated and results in a progressive decrease in visual acuity, especially in distance vision, which can be corrected by myopic toric lenses, and is often misdiagnosed as compound myopic astigmatism and delayed in treatment. The myopic astigmatism glasses fitted will soon be insufficient, manifested by the deepening of the degree, especially the increase in astigmatism is obvious. In the late stage, the posterior elastic lamina of the central part of the cornea can be ruptured at any time, and the atrial fluid enters into the corneal stroma, and acute corneal edema and turbidity suddenly occurs, which leads to a drastic decrease in visual acuity. After healing, corneal scarring and clouding will remain, irregular astigmatism is aggravated, and visual acuity is further reduced. Under the slit lamp microscope, the cornea shows a cone-shaped anterior protrusion, the cone is usually restricted to the central part of the cornea, the top of the cone is located in the central part of the cornea, or the paracentral part of the cornea is located in the central part of the cornea, and the top of the cone is protruding, thinning, and the thickness of the cone is only 1/5 to 1/2 of the normal one. when the patient looks down, the top of the corneal cone presses the lower eyelid margin, so that the lower eyelid margin appears a “V” shaped downward concavity. When the patient looks downward, the top of the corneal cone presses on the lower lid margin, causing a “V” shaped depression in the lower lid margin. Keratoconus examination reveals that the anterior curvature of the cornea is highly variable and irregular, with a K value of more than 70 D. The shadow movement can be seen as scissor-like. Specialized refractive institutions are becoming more rigorous in screening surgical patients for conical corneas. How to recognize that you may have cone cornea? 1. Significant increase in diopters in recent years, frequent change of lenses, especially increase in astigmatism; 2. Corneal thickness <500um by keratometry; 3. Best corrected visual acuity less than 1.0. Early stage of cone cornea: 1. No signs of cone cornea by slit lamp examination, and the corrected visual acuity is ≥0.8. 2. The corneal topography has the following characteristics: the center of the cornea, the cornea below or above the central region of the cornea becomes obviously steeper, and combined with one of the following conditions: 1) the distance from the cornea to the cornea, and 1) the cornea is not very steep. One of the following conditions: ① the difference between the refractive power of the cornea above and below 3mm from the center of the cornea is >3,0D. ② the maximum refractive power of the cornea is ≥47,0D, or the thickness of the cornea at the steepest point is <500 μm. ③ the contralateral eye is in the clinical stage of conical cornea. Clinical cone cornea diagnosis based on: 1, the Department of congenital anomalous eye disease, vision loss; 2, corneal apical thinning, conical bulge; 3, keratoconus meter examination, often found irregular astigmatism, Placido (Placido) corneal disk examination, the concentric ring on the cornea become pear-shaped; 4, slit lamp examination, visible corneal cone top of the posterior elastic lamina propria fissure, stromal clouding. 5, corneal topography: in the last decade or so, the development of computer-assisted corneal topography technology has provided a more detailed and reliable test basis for the diagnosis of subclinical stage conical cornea. The data collected from thousands to tens of thousands of corneal monitoring points are statistically analyzed by internal computer software, reflecting the corneal morphology through color-coded graphics and three-dimensional graphics, describing the curvature changes of the cornea visually and quantitatively, and not only displaying the shape of the corneal surface, but also providing, for example, the simulated corneal K-value (SimK1, SimK2), the Surface Regularity Incentive (SRI), Surface Asymmetry Index (SAI), different diameters of circumferential corneas, and the cornea's surface shape, as well as the surface irregularity index. Some of them are also equipped with cone cornea diagnostic program, which can screen out highly suspicious patients with cone cornea. The anterior corneal deformation forms high myopia and irregular astigmatism, which seriously interferes with the visual function, and the cornea is elliptical curved, and the anterior protrusion of the central cornea is conical. Currently, the two main treatments for conical cornea are refractive correction and corneal transplantation. The former includes wearing framed glasses and corneal contact lenses, intracorneal ring implantation, excimer laser corneal surface keratomileusis (PRK), etc. These methods can achieve refractive correction for some patients with conical cornea, but they cannot stop the progression of the disease. Depending on the progression of the disease, myopia caused by conical cornea in the early stages of the disease can be satisfactorily corrected with frame glasses. When the corneal surface becomes irregular astigmatism, corneal contact lenses can be worn. ①Rigid corneal contact lenses, when the patient has irregular astigmatism, frame glasses can no longer improve the vision, it is necessary to choose the appropriate rigid corneal contact lenses. ② Soft corneal contact lenses. However, since soft corneal contact lenses are soft, the curvature of the lenses tends to become the same as the curvature of the corneal surface, so the improvement of visual acuity is often unsatisfactory when correcting high astigmatism caused by conical cornea. Penetrating corneal transplantation When cone cornea is in advanced stage, corneal transplantation is the only option to restore visual function. Penetrating corneal transplantation has long been recognized as an effective treatment for conical cornea. PKP can stop the progression of the lesion and most patients have good visual recovery, but the postoperative optic outcome and refractive status are difficult to predict and control. Plate-layer corneal transplantation implanted the donor corneal stroma and epithelial tissue into the posterior elastic lamina of the recipient with no or small amount of corneal stroma implantation bed, maximizing the preservation of the recipient corneal endothelial cells, and reducing the incidence of rejection, with low requirements for donor material, either fresh corneal material or dry preserved corneal material, with few intraocular complications, and in the event of failure, it can be replaced by penetrating corneal transplantation, which can be a substitute for penetrating corneal transplantation. It can be used as an alternative treatment to penetrating corneal transplantation. Therefore, the treatment principle of conical cornea is as follows: in the early stage, the vision can be corrected by lenses or corneal contact lenses; for those with heavy irregular astigmatism and central corneal clouding, surgical treatments are feasible, such as lamellar corneal transplantation or penetrating corneal transplantation. The success of corneal transplantation is also related to the quality of the corneal transplant material.