Corneal-Based Procedures: Astigmatic Keratotomy, LASIK, PRK, and SMILE

7 Corneal-Based Procedures: Astigmatic Keratotomy, LASIK, PRK, and SMILE

Jennifer Loh and William B. Trattler

Abstract

Corneal-Based Procedures: Astigmatic Keratotomy, LASIK, PRK, and SMILE is a chapter that is focused on the correction of residual refractive error in patients who have previously undergone cataract surgery. While improvements in IOL calculations have resulted in a higher percentage of patients with excellent uncorrected vision after cataract surgery, there are still a small percentage of patients who have residual refractive error that results in unsatisfactory uncorrected vision. Patients can consider a variety of options to improve their vision, including glasses, contact lenses, intraocular surgery, and corneal refractive surgery. This chapter focuses on the preoperative evaluation and corneal refractive surgery options for patients who desire improvement in their uncorrected vision. While all surgeries carry a small degree of risk, the overall risks with corneal refractive surgery is on the low side, making this an appropriate option for patients who desire improvement in their vision and understand that there are uncommon but serious risks with surgery. The chapter should help the cataract and refractive surgeon in the evaluation and management of patients, and hopefully lead to successful visual outcomes.

Keywords: LASIK, PRK, SMILE, enhancement, EBK, cataract surgery, pseudophakia

7.1 Introduction

This chapter deals with the technique of corneal-based refractive procedures for the correction of residual refractive error. It will also highlight the application of femtosecond lasers for achieving precision and predictable results by customizing the incisions for reproducible results. The shortcomings of the procedure will also be highlighted, as all the patients who need an enhancement procedure are not suited for a corneal touch-up procedure.

7.2 Exceeding Patient Expectations for Cataract Surgery

Expectations for exceptional vision after cataract surgery are very high, especially in patients who have healthy eyes prior to surgery. Over the last two decades, cataract surgery has become both a vision restoration procedure and a vision optimization procedure. Patients who have worn glasses and contact lenses their entire lives can experience a reduced need for vision correction following cataract surgery. However, despite wonderful outcomes for the vast majority of patients, there is a small percentage of patients who end up dissatisfied with their visual results, as they require spectacles or contact lenses to achieve satisfactory vision. When the cause of the dissatisfaction is due to residual refractive error after cataract surgery, it is fortunate that there are a number of surgical and nonsurgical options to improve vision. It is of course important to evaluate patients and determine whether patients are appropriate candidates for vision correction procedures.

The ability for cataract surgeons to leave patients with minimal refractive error has improved over the past decade. First, evidence was developed that a high percentage of patients presenting for cataract surgery had preexisting dry eye, resulting in reduced accuracy of preoperative corneal shape measurements.1 When preoperative tests reveal telltale signs of inaccuracy, patients can be treated for dry eye, and return for repeat measurements 2 to 4 weeks later ( Fig. 7.1, Fig. 7.2). A second improvement for surgeons has been advancements in intraocular lens (IOL) calculation formulas. The latest-generation formulas, including the Hill-radial basis function and Barrett Universal II provide improved visual outcomes over a wide range of axial lengths, corneal steepness values, and anterior chamber depth.² A third improvement over the past decade has been intraoperative aberrometry, which surgeons report can significantly improve visual outcomes.3 All of these advances have helped improve the chance a patient will end up on target, but there are still a small percentage of patients who remain off target and unhappy with their visual outcomes.

Fig. 7.1 Pre-op topography of an 86-year-old female: initial consultation for cataract surgery.

Fig. 7.2 Dry eye identified 1 month later after topical steroids for 1 week and cyclosporine twice daily for 1 month. Two-diopter shift in intraocular lens power (from 18.5 to 20.5 diopters).