Visual function and higher-order aberrations in eyes after corneal transplantation: How to improve postoperative quality of vision

An understanding of corneal optics is important to optimize the visual outcome after eye surgery. Recent advances in the surgical techniques of lamellar keratoplasty have changed the strategies used for corneal transplantation. Lamellar keratoplasty has the advantage of having a lower rate of graft rejection, superior biomechanical properties, and reduced higher-order aberrations (HOAs) compared with penetrating keratoplasty; thus, the use of lamellar keratoplasty has increased over the last 15 years. However, some patients have poor postoperative visual acuity despite a clear cornea, and the reasons for the poor visual outcome are poorly understood. By combining corneal imaging technologies and the latest optical software, we proposed the concept of "parallelism of anterior and posterior surfaces in lamellar keratoplasty." In physiologically normal eyes, in which the anterior and posterior surfaces are parallel to each other, the posterior surface of the cornea compensates the HOAs of the anterior surface, and this is also true in eyes after penetrating keratoplasty. However, after lamellar keratoplasty, in which the anterior and posterior surfaces are independent and not parallel, irregularities in the posterior surface increase the HOAs of the anterior surface. This article introduces this concept to enhance our understanding of visual optics in eyes after penetrating and lamellar keratoplasties and how to apply this concept to surgery to improve and optimize patient visual outcomes.