Corneal asphericity and the effects of the corneal refractive surgery on it

The corneal asphericity refers to most normal corneal surface is an aspherical flat oval, which is helpful to improve the visual quality.In most cases, corneal aspherical coefficient Q-value is negative, and different normal Q-value is reported in literatures, corneal Q-value is influenced by many factors, quadrants have great effects on it, the influence of age is weak, there are correlation between myopic degree, ocular axial length, radius of curvature, intraocular pressure and Q-value.The corneal refractive surgery is one of the most important methods to correct refractive errors, but it has negative effects on the corneal asphericity, and then results in glare, visual quality degradation and other issues.Different corneal refractive surgeries would have different effects on the corneal asphericity.Wavefront aberration-guided femtosecond laser in situ keratomileusis（LASIK) surgery and Q-value guide LASIK are superior to standardized LASIK, the change of Q-value after femtosecond lenticule extraction（FLEx) surgery is less than that after wavefront aberration guided LASIK.The influence of femtosecond laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) on Q-value are rarely reported.In addition, the Q-value changes from negative to positive after corneal refractive surgery of myopia, the variation tendency is opposite after hyperopia surgery.Q-value variation is highly correlated to spherical equivalent, the impact of laser and healing still needs further exploration.In order to further exploring of the corneal asphericity and getting a better effect of surgery, here is a review about normal corneal asphericity and the effects of the corneal refractive surgery on it.