The goal of modern cataract surgery is for patients to achieve distance, intermediate, and near vision without correction. In the past few years, we have witnessed a dramatic increase in implantations of newer IOL models that allow patients greater opportunity to live without glasses—presbyopiacorrecting lenses. However, spectacle independence cannot be promised without the use of appropriate techniques for astigmatism correction. Is there still room for conventional limbal relaxing incisions (LRIs) in the era of excimer and femtosecond laser technology?
LIMBAL RELAXING INCISIONS
Corneal relaxing incisions, also called astigmatic keratotomy, have been used for decades to reduce high preexisting corneal astigmatism in cataract patients.1 Single or paired arcuate incisions are placed concentric to the visual axis to a depth of 90% of the thinnest pachymetry measurement. Corneal relaxing incisions correct relatively high astigmatism, but they have limited predictability, especially for lower cylindrical refractive errors.
In the 1990s, surgeons began to move the location of relaxing incisions to the limbus. LRIs (Figure 1) produce less astigmatism correction than corneal incisions; however, they result in smoother corneal topographies and less corneal irregularity. They have a better safety profile, are easier to perform, and are more comfortable for the patient than corneal incisions. Additionally, precise on-axis placement of LRIs is not as crucial because of their length (4–12 mm). Several nomograms have been developed to improve predictability and clinical outcomes.
LRIs are a well-established refractive incisional technique for astigmatism correction2 most commonly performed at the time of cataract surgery with implantation of a monofocal, multifocal, or accommodating IOL. How does their performance compare with toric IOLs? My study3 revealed that both methods are predictable and effective in correcting preexisting corneal astigmatism up to 3.00 D, with high patient satisfaction in both groups; however, the toric IOL group achieved significantly better results in UCVA, contrast sensitivity, subjective residual refraction, and spectacle independence for distant vision. Table 1 summarizes advantages and disadvantages of both procedures. Other options for intraoperative astigmatism correction, such as clear corneal incisions in the steep axis or opposite clear corneal incisions, are used only in selected cases.
Premium IOLs are usually a synonym for presbyopiacorrecting IOLs, although some surgeons include toric IOLs in this category. There are many presbyopia-correcting–lens concepts, including refractive and diffractive multifocal IOLs and accommodating IOLs, which are, at this time, more appropriately called pseudoaccommodating IOLs.
Just 10 years ago in the United States, only one zonal refractive multifocal IOL was available (Array; Abbott Medical Optics Inc., Santa Ana, California; no longer available). In 2005, three premium lenses were approved by the US Food and Drug Administration (FDA): a single-optic accommodating lens (Crystalens; Bausch + Lomb, Rochester, New York), a zonal refractive multifocal IOL (ReZoom; Abbott Medical Optics Inc.), and a diffractive multifocal IOL (AcrySof Restor; Alcon Laboratories, Inc., Fort Worth, Texas). More recently, an aspheric diffractive lens (Tecnis Multifocal; Abbott Medical Optics Inc.) became available.
These same lenses are available in Europe, where they are the most popular presbyopia-correcting IOL models; however, we have a larger selection of presbyopiacorrecting lenses compared with our peers in the United States. Many accommodating lenses have received the Conformité Européenne (CE)-Mark but are awaiting FDA evaluation, such as the Akkommodative 1CU (HumanOptics AG, Erlangen, Germany), the Tetraflex (Lenstec, St. Petersburg, Florida)m and the dual-optic Synchrony (Abbott Medical Optics Inc.).
We also have additional multifocal lens technologies in Europe, including the AT.LISA (Carl Zeiss Meditec, Jena, Germany), M-flex (Rayner Intraocular Lenses Ltd., East Sussex, United Kingdom), and Lentis Mplus (manufactured and distributed by Oculentis GmbH, Berlin, and Topcon Europe, Rotterdam, Netherlands). The latest approval in the European market is the first multifocal toric IOL, the M-flex T; European surgeons are also anticipating approval of the AT.LISA toric and awaiting the official launch of the Mplus Toric at the World Ophthalmology Congress in Berlin in June.
DO LRI S AND PRESBYOPIA-CORRECTING
IOLS WORK TOGETHER?
Preoperative corneal astigmatism of 1.00 D or more is the most common contraindication for implantation of multifocal or accommodating IOLs. Multifocal IOLs are especially sensitive to residual cylindrical refractive error resulting in patient dissatisfaction and postoperative spectacle dependence.
About 30% of eyes undergoing cataract surgery have at least 1.00 D of astigmatism,4 and eliminating visually significant corneal astigmatism is one of the key factors in successful premium IOL implantation. These facts have led physicians to revisit LRIs as an option to treat preoperative corneal astigmatism at the time of cataract surgery. My own unpublished results using the Nichamin age- and pachymetry-adjusted (NAPA) nomogram show a reduction of mean corneal astigmatism from 2.19 D to 0.98 D. Muftuoglu et al5 provide stronger evidence of success with LRIs in conjunction with premium IOLs, with the preoperative mean keratometric astigmatism of 1.30 ±0.68 D reduced to 0.59 ±0.48 D postoperatively. Some eyes with higher corneal astigmatism (28.7%) required subsequent LASIK for residual refractive error correction.
Postoperative laser vision correction after implantation of presbyopia-correcting IOLs is a viable strategy for patients with significant preoperative corneal astigmatism. However, the main disadvantage is the need for and cost of an additional surgical procedure. It is essential to inform the patient of the possibility of the need for further intervention before cataract surgery. Muftuoglu5 shows that laser enhancement can successfully be done after previously performed LRIs.
LRIs are a predictable and effective means of correcting preexisting corneal astigmatism up to 2.00 D at the time of presbyopia-correcting IOL implantation. However, some eyes may require further laser enhancement. LRIs may increase the percentage of patients who fulfill inclusion criteria for premium IOLs and improve clinical outcomes in these patients. Another option that is worth recommending is postoperative laser enhancement, which can also be done after LRIs. Further development of premium IOLs, such as the recent introduction of toric multifocal lenses, will diminish the need for both LRIs and laser enhancements in the future.
Bartlomiej J. Kaluzny, MD, is an Assistant Professor, Department of Ophthalmology, Collegium Medicum, Nicolas Copernicus University, Poland, and Consultant Ophthalmic Surgeon, Oftalmika Eye Hospital, Poland. Dr. Kaluzny states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: email@example.com.