Evaluation of Toric Intraocular Lenses in Patients With Low Degrees of Astigmatism

ORIGINAL CLINICAL STUDY Evaluation of Toric Intraocular Lenses in Patients With Low Degrees of Astigmatism Lewis Levitz, MBBCh, MMed,* Joe Reich, MBBS, DO,* Kate Roberts, BOrth,* and Chris Hodge, BAppSc (Orth)*Þ Purpose: This study aimed to describe the efficacy of toric intraocular lenses (IOLs) in patients with low degrees of corneal astigmatism. Design: Retrospective case series was undertaken. Methods: Patients with low amounts of corneal astigmatism who were treated with either a toric monofocal lens (SN6AT2 Toric, n = 76) or a toric multifocal lens (SND1T2 +3.00, n = 44) were reviewed. Eyes were evaluated preoperatively and 3 months postoperatively. Refraction and visual outcomes were monitored. Results: Patients (69.7%) in the monofocal toric group obtained refractive cylinder less than 0.25 diopters (D) compared with 70.5% of the multifocal toric group. Both toric groups showed a statistically significant reduction in refractive cylinder after surgery (P = 0.001). Monofocal (66.7%) and multifocal (68.2%) toric patients achieved uncorrected distance visual acuity of 20/20 or better. Conclusions: This represents the first article to investigate the use of low-power toric IOLs in patients with less than 1.25 D of corneal cylinder. Before the development of low-power toric IOLs, patients with low to moderate amounts of astigmatism required concurrent intraoperative adjustments or additional forms of treatment to benefit from cataract and IOL surgery. Evidence suggests that the toric T2 IOL now removes this barrier, providing consistent, accurate refractive and astigmatic results, and enables these patients to achieve excellent outcomes with a single treatment across IOL platforms. Larger studies will help to consolidate our results. Key Words: cataract, toric IOLs, astigmatism (Asia Pac J Ophthalmol 2015;4: 245Y249) Driven both by patient and surgeon expectations, the demand for so-called premium intraocular lenses (IOLs) continues to increase. 1 The optimization of these lenses, which include multifocal, accommodating, and toric IOLs, is dependent on the ability of the surgeon to minimize postoperative refractive error, in particular astigmatism. 2 Small residual errors of 0.5 D refractive astigmatism have been reported to reduce visual acuity by up to 1 line of LogMAR acuity. 3 Counter to these findings though, it has been suggested that low levels of residual cylinder may actually serve to increase the depth of focus and assist some patients. 4 Several methods to treat astigmatism at the time of surgery exist, including the placement of primary incisions on the steep meridian of the cornea, From the *Vision Eye Institute, Hawthorn East, Melbourne, Victoria; and Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia. Received for publication April 8, 2014; accepted January 16, 2015. The authors have no funding or conflicts of interest to declare. Reprints: Lewis Levitz, MBBCh, MMed, Vision Eye Institute, 27 Denmark Hill Rd, Hawthorn East, Melbourne, Victoria 3123, Australia. E-mail: lewis.levitz@visioneyeinstitute.com.au. Copyright * 2015 by Asia Pacific Academy of Ophthalmology ISSN: 2162-0989 DOI: 10.1097/APO.0000000000000112 peripheral corneal relaxing incisions, and the implantation of toric IOLs. The successes of toric IOLs for moderate to high degrees of astigmatism have been reported. 5Y7 More recently, toric and multifocal toric IOLs for low levels of astigmatism have been available to surgeons. As approximately two thirds of the population will have corneal astigmatism levels of 1 D and below, 8,9 these IOLs represent a significant opportunity to improve potential patient refractive outcomes. The final refractive result for toric IOL implantation may be mitigated by several factors. Inaccurate or fluctuating preoperative keratometry, 10 underestimation of the total astigmatism power in IOL calculations, 11Y13 errors in IOL positioning, 14 IOL instability, 15 and unexpected surgically induced astigmatism 16 have been reported to decrease the effectiveness of the procedure. These errors may acquire more importance when low degrees of astigmatism are corrected. This study reviews a series of patients with low degrees of corneal astigmatism undergoing monofocal and multifocal IOL implantation with either the AcrySof T2 (SN6AT2) or the toric multifocal ReSTOR (SND1T2) to establish the potential benefit of the astigmatic correction in these cases. MATERIALS AND METHODS A retrospective, consecutive evaluation of patients undergoing cataract removal and implantation of low-power toric IOLs was undertaken. The files of 2 groups of patients were examined: those who were implanted with a toric monofocal IOL (SN6AT2; Alcon, Fort Worth, TX) or those with the multifocal IOL (SND1T2 Toric ReSTOR +3 D). Patients were excluded from analysis if their visual potential was limited by known ocular pathology such as corneal scarring or retinal disease. A total of 120 eyes were assessed. Before surgery, patients underwent a comprehensive ocular evaluation including biometry and keratometry assessment. Preoperative keratometry was measured using the IOLMaster (V5.0 Carl Zeiss Meditec, Jena, Germany). Dependent on surgeon choice, either the SRK/T or Holladay II formulas were used for lens power calculations for all patients. The Alcon AcrySof Toric Calculator (http://www.acrysoftoriccalculator.com/calculator.aspx) was used to confirm the required cylindrical power. Previous clinical audits suggested a consistent surgical-induced astigmatism value of j0.3 D. This value was added to preoperative toric calculations as a standard procedure. The surgeries were performed by 4 surgeons (L.L., J.R., A.T., and R.P.) at the same surgical facility. Surgery was performed under peribulbar anesthesia using a 2.75-mm standard clear corneal incision. The main incision was placed temporally at 180 and 0 degrees for the right and left eyes, respectively. The patient s steep keratometric axis was identified and marked with a Codman surgical marker pen (Johnson & Johnson, Raynham, MA) at 6- and 9-o clock positions on the limbus. Intraoperatively, the steep corneal axis was then marked using the Mendez marker. Asia-Pacific Journal of Ophthalmology & Volume 4, Number 5, September/October 2015 www.apjo.org 245

Levitz et al Asia-Pacific Journal of Ophthalmology & Volume 4, Number 5, September/October 2015 TABLE 1. Preoperative and Postoperative Refractive Data Monofocal Toric IOL Group Multifocal Toric IOL Group Factors Mean T SD Range Mean T SD Range Preoperative sphere 0.27 T 2.26 j6.00 to 4.50 2.34 T 1.02 1.00 to 5.00 Preoperative cylinder j0.67 T 0.61 j1.50 to 0.00 j0.50 T 0.43 j1.50 to 0.00 Preoperative SE j0.06 T 2.24 j6.38 to 4.00 2.09 T 0.99 0.75 to 5.00 Preoperative keratometry 43.90 T 1.36 41.52 to 47.15 43.94 T 1.25 41.61 to 47.24 Preoperative corneal cylinder 0.74 T 0.21 0.40 to 1.18 0.47 T 0.19 0.23 to 1.08 Postoperative sphere j0.26 T 0.54 j2.25 to 1.00 0.05 T 0.32 j0.50 to 0.75 Postoperative cylinder j0.19 T 0.30 j1.00 to 0.00 j0.19 T 0.30 j1.00 to 0.00 Postoperative SE j0.33 T 0.50 j0.75 to 0.50 j0.04 T 0.32 j0.75 to 0.75 Arithmetic difference from intended j0.05 T 0.44 j1.33 to 1.26 0.00 T 0.43 j1.50 to 1.00 Absolute difference from intended 0.32 T 0.29 0.00 to 1.33 0.30 T 0.29 0.00 to 1.50 Postoperative results were taken at 3 months. Refraction and visual outcomes were monitored. For further analysis, preoperative corneal astigmatism data were designated into 3 groups as follows: with the rule (WTR), against the rule (ATR), and oblique (OBL). Statistical analysis was performed using SPSS V20 (SPSS, IBM, USA). Student t tests were used to determine the difference in mean postoperative values among groups. A P value of 0.05 was considered statistically significant. RESULTS Forty-four eyes of 44 patients (20 men, 24 women) were included in the toric multifocal IOL cohort and 76 eyes of 63 patients (29 men, 34 women) were included in the toric monofocal group. Refractive Data Preoperative and postoperative refractive data are included in Table 1. Monofocal IOL group patients (77.9%) achieved a postoperative spherical equivalent (SE) within plus or minus 0.5 D and 94.7% of patients had refractive cylinder within plus or minus 0.5 D. The multifocal group (93.3%) fell within 0.5 D of the intended SE postoperatively and 88.7% of patients had refractive cylinder within plus or minus 0.5 D. Figure 1 shows the attempted versus achieved SE graphs for both groups, reflecting the close agreement between preoperative aims and postoperative outcomes. Both toric IOL cohorts showed a statistically significant reductioninrefractivecylinderaftersurgery(p = 0.001). Figure 2 details the distribution of postoperative astigmatism of both groups. Figure 3 outlines the preoperative refractive astigmatism as determined by the corneal astigmatic orientation. The change was relatively consistent across monofocal toric patients. In the multifocal toric cohort, the with the rule and against the rule patients noticed a decrease in refractive astigmatism; however, those patients who had preoperative oblique corneal astigmatism showed minimal, if any, change. The difference is likely a reflection of the small sample size of oblique patients in the multifocal cohort rather than a significant difference in IOL or method. FIGURE 1. Spherical equivalent refraction, attempted versus achieved (D). A, Attempted versus achieved for spherical IOL group only. B, Attempted versus achieved for toric IOL group only. FIGURE 2. Distribution of postoperative refractive cylinder. 246 www.apjo.org * 2015 Asia Pacific Academy of Ophthalmology

Asia-Pacific Journal of Ophthalmology & Volume 4, Number 5, September/October 2015 Evaluation of Toric IOLs FIGURE 3. Preoperative (left) and postoperative (right) refractive astigmatism by corneal astigmatic correction. Visual Acuity Preoperatively, 38% of patients in the monofocal group achieved 20/20 corrected distance acuity. Approximately 80% of multifocal patients achieved corrected distance visual acuity of 20/20 or better, which reflects on the subset of patients demanding multifocal IOL implantation. Postoperatively, 60.3% and 68.2% of eyes achieved 20/20 or better uncorrected visual acuity in the monofocal and multifocal groups, respectively. As a measure of the multifocal IOL group, 70.5% of patients achieved N5 or better at 3 months after surgery. Figure 4 describes the postoperative uncorrected distance visual acuity (UDVA) for both groups and the uncorrected near visual acuity (UNVA) for the multifocal group. DISCUSSION The goal of optical independence after surgery has quickly become a focus for surgeons and patients. Advances in IOL technology have helped surgeons achieve these aims with greater accuracy and consistency. Available since the early 1990s, 17 multifocal IOLs have shown good distance, intermediate, and FIGURE 4. Cumulative postoperative uncorrected visual acuity (distance top, near bottom). * 2015 Asia Pacific Academy of Ophthalmology www.apjo.org 247

Levitz et al Asia-Pacific Journal of Ophthalmology & Volume 4, Number 5, September/October 2015 near visual results across many published studies. 18Y20 Although astigmatic corrections have been incorporated in most multifocal models, most have a cylindrical power of 1.50 D or higher. 21 Paradoxically, this limits patients who have low levels of corneal and refractive cylinder interested in achieving complete optical independence. With approximately two thirds of the population having corneal cylinder values of less than 1 D, 8,9 a significant portion of patients may be left with residual refractive astigmatism after surgery if a spherical IOL is used. Recently, Alcon has produced an IOL with a refractive cylindrical component of 1 D, which equates to 0.68 D at the corneal plane. In our retrospective assessment, we provide preliminary evidence to suggest that this lens can be used effectively in patients with low degrees of corneal astigmatism and report excellent visual results. A combined 64.3% of patients obtained UDVA of 20/20 or better after surgery with the multifocal toric IOL. This compares well with Visser et al 21 who provide an overview of recent toric IOL results, albeit with higher preoperative levels of astigmatism. In their review, between 5% and 63% of cases achieved UDVA of 20/20 or better. In our group, between 65% and 70% of patients had a residual cylinder of 0.25 D or less and 90% had less than 0.5 D. These values compare favorably with previous studies; however, the comparison is mitigated again by the higher levels of preoperative cylinder in any comparison study. In isolation, however, there was a significant difference between preoperative and postoperative values in our toric group, which suggests that surgeons can expect to improve upon visual outcomes when using the low-powered toric lens. There are several considerations for the use of toric IOLs. Misalignment of the IOL can lead to residual astigmatism. 18 This may occur intraoperatively or after postoperative rotation of the IOL. Changes in IOL design and biomaterial have significantly reduced the relative instability of lenses. 22 Accurate keratometry assessment, preoperative marking, and placement of the IOL will facilitate better postoperative results. Inherent errors in IOL calculations will also contribute to reducing the effectiveness of outcomes. Goggin et al 23 recently identified an underestimation of the corneal plane cylinder power of the IOLs by the manufacturer s available calculation program. Koch et al 12 outlined the potential influence of posterior corneal astigmatism on postoperative results. Identification of these artifacts in combination with new technology will likely see our results improve further. There remain several options for correcting astigmatism in conjunction with cataract surgery. Intraoperative corneal relaxing incisions have been used extensively to treat astigmatism. 24,25 The use of incisions can present several challenges, including the placement of incisions which may be technically difficult in certain meridians 26 and induction of higher order aberrations. Grabow 27 also highlights concerns with the longterm stability of the incisions. Furthermore, recent studies have suggested that toric IOLs will provide significantly better UDVA, improved contrast sensitivity, and more consistent results. 28,29 Our results add to the current body of literature to suggest toric IOLs may represent a superior long-term option. Our study has limitations. The sample is small and retrospective in nature. Larger, prospective trials will help confirm the putative benefits of this technology. Surgery was performed by 4 separate surgeons albeit following similar guidelines. This may have contributed to residual noise or artifacts within our observations. 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