4 Residual Refractive Error Abstract This chapter discusses the causes of residual refractive error after cataract surgery and the surgical strategies that can be utilized by the modern-day ophthalmologist to manage and correct this unintended pseudophakic ametropia. Keywords: residual refractive error, LASIK, PRK, arcuate keratotomy, IOL exchange, piggyback IOL, toric IOL, light-adjustable IOL Continued research efforts to further advance and refine technologies and techniques within cataract surgery have significantly optimized postoperative refractive outcomes over time. However, even in the hands of the most experienced and skilled surgeon, a subset of patients may still be left with residual refractive error that negatively affects vision.1 Fortunately, there is currently an unprecedented number of strategies available for managing residual refractive error, each of which can yield favorable results when implemented appropriately. Prior to pursuing any treatment, it is critical for the surgeon to first determine the cause of refractive surprise so that the most appropriate management can be selected. In general, pseudophakic residual refractive error may be the result of preoperative, intraoperative, and/or postoperative causes. Preoperative causes include biometry errors leading to inaccurate axial length or keratometry readings, which subsequently affect the calculation of intraocular lens (IOL) power.2 Similarly, failure to recognize corneal pathology or elicit a history of prior keratorefractive surgery will lead to inaccurate topographic and keratometric measurements. Intraoperative causes include incorrect positioning of the IOL, misalignment of a toric IOL, or, more uncommonly, inadvertent selection of the incorrect IOL power. Postoperatively, changes in the final IOL position can occur during the healing process due to capsular bag fibrosis. Once the cause of refractive error has been determined, an individualized treatment plan can be tailored to meet the needs of the particular patient. Initially, conservative measures such as the use of spectacles or contact lenses should be attempted. For those patients who cannot or will not tolerate such noninvasive methods, surgical correction must be considered. Surgical strategies for the correction of residual refractive error can be thought of in two general categories: (1) cornea-based approaches and (2) lens-based approaches. Keratorefractive approaches for correcting pseudophakic ametropia include laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Both of these procedures have been extensively studied for their use in the correction of a wide range of refractive errors and have demonstrated excellent safety, efficacy, and predictability.3 Laser refractive surgery not only avoids additional intraocular surgery and its inherent associated risks, but also appears to provide better accuracy when compared to IOL exchange or piggyback lens techniques. Specifically, LASIK-treated eyes have demonstrated superior predictability, with 93% of eyes achieving a final spherical equivalent (SE) within ±0.50 diopters of emmetropia, when compared to lens-based procedures.4 Furthermore, LASIK is preferable in eyes that have previously undergone neodymium:YAG capsulotomy, where IOL exchange becomes more difficult with greater risk of intraoperative complications.5 Refractive surgery does, however, have some disadvantages, including its limited ability to correct large spherical errors. In addition, the older patient population that undergoes cataract surgery may be more susceptible to tear film abnormalities that can develop after corneal ablative procedures. In those patients whose ametropia is composed primarily of cylindrical error, arcuate keratotomy can be performed, either manually or with femtosecond technology, to correct this residual corneal astigmatism. In fact, a recent study found femtosecond laser-assisted arcuate keratotomy to be as effective as implantation of a toric IOL in correcting corneal astigmatism.6 Implantation of the incorrect IOL power and IOL dislocation/decentration are currently the two most commonly reported indications for IOL exchange after cataract surgery.7 However, as multifocal IOLs become increasingly popular, patient dissatisfaction from resulting higher-order aberrations such as glare and halos is contributing to an ever-increasing proportion of IOL exchange cases. Nonetheless, given the risks associated with further intraocular surgery, it is preferable to reserve IOL exchange to patients who require large ametropic corrections or those with severe corneal disease prohibiting them from receiving keratorefractive surgery. In all cases, IOL exchange is best performed soon after the initial surgery when the original cataract wound can be reopened and capsular-IOL adhesions have not yet formed. The piggyback technique that involves the implantation of a second IOL not only can be used to correct high levels of refractive error, but also offers several additional advantages, including improved ease of surgery, relative simplicity of IOL power calculation, and reversibility of the procedure. Furthermore, recent studies have shown piggyback IOLs to be more effective and accurate than IOL exchange, with a higher percentage of eyes achieving 20/20 uncorrected distance visual acuity or better (33 vs. 18%) and an SE within ±0.50 diopters of emmetropia (92 vs. 82%).8 Potential drawbacks of this approach, however, include the risk of developing postoperative interlenticular opacities, pupillary block, pigment dispersion, or secondary glaucoma. Refractive surprise after implantation of a toric IOL can occur due to a variety of reasons including preoperative measurement error, alignment error, IOL rotation, or surgically induced astigmatism. In cases of alignment error or IOL rotation, prompt diagnosis on the part of the surgeon is essential so that IOL orientation can be corrected in a timely manner postoperatively. However, it is important to remember that rotation of a toric IOL can also be an effective tool for treating residual refractive error in cases not involving axis misalignment, but rather corneal topographical changes over time, such as Salzmann’s nodular degeneration or pterygium.9 Another emerging lens-based technology is the light-adjustable IOL, which introduces the possibility of correcting postoperative ametropia in a noninvasive way. Using this technology, the refractive power of the IOL can be titrated using ultraviolet light based on the individual requirements of each patient postoperatively with correction of up to 2.0 diopters of refractive error ( Paralleling the advance of technology, patient’s expectations after cataract surgery also continue to grow. As a result, ophthalmologists must be prepared to manage unintended pseudophakic ametropia. Familiarity with the causes and surgical treatment options for residual refractive error should therefore be an essential component of every modern-day cataract surgeon’s armamentarium. • It is critical to first determine the cause of refractive surprise so that the most appropriate management can be selected. • Keratorefractive surgery (LASIK or PRK) avoids the risks of intraocular surgery and yields more effective and predictable outcomes than lens-based procedures.
4.1 Residual Refractive Error
4.2 Causes of Residual Refractive Error after Cataract Surgery
4.3 Management of Residual Refractive Error after Cataract Surgery
4.3.1 Cornea-Based Approaches
Keratorefractive Surgery
Arcuate Keratotomy
4.3.2 Lens-Based Approaches
Intraocular Lens Exchange
Piggyback Intraocular Lens Implantation
Rotation of a Toric Intraocular Lens
Light-Adjustable Intraocular Lens
Fig. 4.1). While this technology is still not yet commercially available in the United States, the results of preliminary international studies are quite promising, demonstrating excellent visual outcomes.10
4.4 Conclusion
4.5 Key Pearls
Ento Key
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