After excimer laser keratomileusis surgery, secondary cone corneal due to continuous corneal dilation is one of the most serious complications after LASIK, which can lead to loss of best corrected vision and even require corneal transplantation in severe cases. Therefore, it is most likely to cause medical complaints and disputes. Professor Seiler first reported post-LASIK corneal dilatation and secondary cone corneas in 1998, and as of 2008, more than 200 cases have been reported in the literature, while the actual number should far exceed this figure, with an incidence of 0.04% to 0.6%. It is now believed that postoperative secondary cone corneas are “chronic biomechanical failure” of the cornea, which can occur from a few days to several years after surgery, with an average of 15 or 3 months. It is characterized by progressive loss of naked and corrected visual acuity, increased myopic and astigmatic refractive error, abnormal bulging in the central and inferior regions of the corneal topography, and thinning of the cornea in the corresponding areas. Risk factors for postoperative secondary cone corneas include: 1) the presence of preoperative subclinical cone corneas, stuttering cone corneas (FFKC), and clear limbal corneal degeneration (PMCD), which account for approximately 88% of all statistical cases; 2) a thin residual corneal stromal bed (less than 250 microns), with particular attention to the fact that the actual corneal flap thickness is too thick due to inaccurate estimates of flap thickness. In particular, it should be noted that the actual corneal flap thickness is too thick due to the inaccurate estimation of the flap thickness, which is the main reason for the insufficient thickness of the preserved corneal stromal bed; 3, young age (less than 25 years old), slightly more men than women; 4, high myopia (-10D or more); 5, thin preoperative cornea (less than 500 microns); 6, reoperation. Preoperative exclusion of occult cone corneas and preservation of sufficient remaining corneal stromal bed thickness during LASIK is the key to preventing postoperative corneal dilatation and even secondary cone corneas due to the corneal structure becoming weak and unstable. The current standard recommendation is to preserve at least 250 mm of subcleral stromal bed thickness after laser ablation, but this thickness is not absolutely safe and should be considered in relation to the preoperative base corneal thickness and base IOP. Recently, some authors have proposed the concept of bearing factor, i.e., bearing factor = preoperative corneal thickness/postoperative subcleral bed thickness, and a bearing factor of less than 2 or 1 is safer. For example, if the preoperative central corneal thickness is 600 mm, the postoperative corneal subflap stromal bed thickness must be preserved at least 286 mm (600/286 = 2,1). Although secondary cone corneas after LASIK are most often seen in cases where higher myopia is corrected, where the preoperative cornea is thin, or where multiple laser ablations have been performed, they have also been reported in patients with corrections as low as -4D and where the remaining corneal stromal bed thickness is also assuredly greater than 250 mm. The reasons for this may be that the microkeratome laminotome created a thicker than expected flap, resulting in a thinner remaining stromal bed; in addition, a subclinical conical cornea or dilatation may have been present preoperatively. Currently, corneal topography (anterior and posterior surfaces) remains the only method to show early cone corneas and is the “gold standard” for screening cone corneas. Before screening for cone corneas, a detailed medical history should be taken. The clinical risk factors for cone corneas are: 1) astigmatism greater than 3D, progressive astigmatism, progressive high myopia; 2) apparently poor optometrically corrected visual acuity; 3) family history of cone corneas; 4) associated diseases such as severe allergic conjunctivitis, lower lid entropion, Down’s syndrome, Marfan’s syndrome, etc. The indicators of anterior surface corneal topography for cone corneal screening are: 1, the local area of the cornea becomes steeper, and its apex is mostly deviated from the center of the visual axis, most common in the lower or inferior temporal area; 2, the central refractive power of the cornea increases, greater than 48, 7D; 3, the lower cornea is significantly steeper than the upper cornea, the I-S value is greater than 1, 9D; 4, the central refractive power difference of the cornea is greater than 0, 92D in both eyes of the same individual. Pathology Histologically, the earliest manifestation of conical cornea is the posterior surface bulge into the posterior elastic layer, at this time, the anterior surface morphology of the cornea can still maintain normal because the corresponding corneal epithelial thinning can compensate for the bulge morphology. In theory, Orbscan II and Pentacam are the earliest diagnostic tools for subclinical cone corneas because of their ability to detect the morphology of the posterior corneal surface. The screening criteria of Orbscan for cone corneas are: 1) asymmetric anterior surface height map with the highest point shifted downward; 2) posterior corneal surface height bulge greater than 50 microns compared to the best-fit reference sphere (BFS); 3) asymmetric corneal curvature map with the steepest point exceeding 48, 7D; 4) thinning below the corneal thickness map (less than 500 microns) with the thinnest point coinciding with the steepest point; 5) irregularity index 3mm area is greater than 1, 5D, 5mm area is greater than 2, 0D. The Pentacam photographic analysis system of the anterior segment of the eye is based on the principle of Scheimpflug imaging, which improves the depth of focus of imaging, and allows direct measurement of the height of the anterior and posterior surfaces of the cornea, as well as the depth of the anterior chamber and the density of the lens through rotational scanning of the anterior segment of the eye. Compared to the best-fit reference sphere (BFS), its anterior surface bulge height is less than 12 microns under normal conditions; the posterior surface bulge height is less than 17 microns. In addition, the presence of a cone cornea is determined by the thickness of the cornea and its distribution pattern as well as the symmetry of the two eyes. There is also an ocular response analyzer (ORA) on the market today, which is a modification of the non-contact IOP meter. In addition to measuring IOP, it can also measure corneal viscoelasticity (CH), and corneal resistance factor (CRF). CH represents the difference between two pressure level measurements, and is the elastic damping force of the cornea, reflecting the viscoelasticity of the cornea (the ability of the cornea to absorb energy); CRF is the cumulative effect of viscoelastic resistance during the process of deforming the cornea. The cumulative effect of viscoelastic resistance in the process of deforming the cornea, reflecting the elasticity of the cornea, the overall resistance of the cornea. In post-LASIK and conical cornea patients, there is a significant decrease in CH as well as CRF. However, because their measurements are influenced by a combination of corneal thickness, ocular stiffness, and viscoelasticity, they have not yet been useful in screening for early cone corneas. In the event of postoperative corneal dilatation or signs of cone corneas, topical medication to lower the underlying IOP and a trial of rigid gas permeable corneal contact lenses (RGP) may be used to prevent further corneal bulging in addition to restoring good corrected visual acuity. Currently, implantation of symmetric or asymmetric intracorneal stromal PMMA ring segments (Intacs) is also being investigated to reduce irregular astigmatism. Cross-linking of corneal collagen (cross-linking) may also be used to increase the strength of the cornea. In severe cases, penetrating corneal transplantation is required.