Currently, there are four main categories of personalized keratomileusis: Q-value guidance, corneal topography guidance, wavefront aberration optimization, and wavefront aberration guidance. Q-value guidance To understand Q-value guided personalized surgery, we must first understand what Q-value is, which is actually a figure representing the shape of the cornea. If our cornea is a standard sphere, the Q value is zero; if the central cornea is flatter than the standard sphere, the Q value is greater than zero, which is a positive value, and the flatter it is, the larger the absolute value of Q value; if the central cornea is more prominent than the standard sphere, the Q value is less than zero, which is a negative value, and again, the more prominent it is, the larger the absolute value of Q value. From the basic theory of aberration, we can learn that the standard sphere will produce spherical aberration, while most normal corneas are not standard spherical, but non-spherical with a slightly protruding center, i.e., the Q value is negative, thus greatly reducing spherical aberration and making the visual effect better. Laser myopia surgery is performed by cutting the central cornea, which reduces the curvature of the central cornea and flattens it to correct myopia, but this also makes the cornea flatten after surgery, i.e., the postoperative Q value develops to a positive value, which increases the spherical aberration and reduces the postoperative visual quality. This reduces the spherical aberration introduced by the surgery and improves the postoperative visual outcome. Therefore, Q-value-guided individualized surgery is also called aspheric individualized surgery. Corneal topography guidance The cornea is not a smooth sphere. In fact, the curvature (curvature) of every point on the cornea is not the same, especially if there is corneal scarring, after corneal trauma, eccentric cutting after refractive surgery, undercorrection, etc., then the cornea will become more irregular. In this case, if the conventional laser surgery cutting pattern is used, it is difficult to achieve the expected result, and sometimes it may even deviate from the expected result completely. Corneal topography-guided personalized surgery is to obtain accurate corneal topography data through a corneal topographer and submit it to a design program to obtain an individualized cutting plan, which will then be transmitted to the excimer laser, and the computer will guide the laser to perform cutting treatment according to the personalized plan, thus obtaining a smooth and flat corneal surface, reducing higher-order aberrations and improving postoperative visual quality. Wavefront optimization Because the cornea is a curved aspheric shape, when the laser is used for tissue cutting, the same laser spot falling on the central cornea and the peripheral cornea will have different effects, and the shape and energy of the laser spot falling on the periphery will change (the periphery is further away and more inclined than the central path), resulting in higher-order aberrations after surgery. Wavefront optimization is a technique that compensates for the change in corneal curvature with additional energy when cutting the peripheral area to reduce the formation of higher-order aberrations and improve postoperative visual outcomes. Wavefront optimization is in fact a personalized procedure often referred to as K-value guidance. Fourth, wavefront aberration guidance Simply understand, aberration is the difference between the object we see and the object itself. Aberration is everywhere, and to exaggerate, all optical problems are ultimately aberration problems. Our eye is also an optical system, and naturally there are many aberrations, such as myopia, hyperopia, regular astigmatism and other refractive errors belong to the lower order aberrations, there are also higher order aberrations such as spherical aberration, comet aberration, clover aberration and so on. Only wavefront aberration-guided personalized surgery can remove the higher-order aberrations that affect vision and visual quality, and further improve postoperative visual quality. Wavefront aberration-guided personalized surgery is performed by capturing the aberration of the entire eye (i.e., eye fingerprint) with a wavefront aberrometer and transmitting the aberration data to the excimer laser system, which guides the laser to perform a personalized scan, thereby significantly increasing the quality of postoperative vision. The above is a brief analysis of the various personalized procedures currently available, and it is actually difficult to decide which is better or worse. As far as my personal understanding is concerned, most of the equipment manufacturers should have incorporated wavefront optimization in their lasers; whether Q-value guidance is effective seems to be controversial, but theoretically, it should reduce spherical aberration; corneal topography guidance, for extremely irregular corneas, has shown its advantages in practical applications; wavefront aberration guidance should be the most promising technology, but there are still However, there are still many problems to be solved, such as how to reduce the aberration introduced by surgery (or precession), how to control the aberration generated by postoperative reaction, etc.