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Comparison of Refractive Stability After Non-toric Versus Toric Intraocular Lens Implantation During Cataract Surgery
Comparison of Refractive Stability After Non-toric Versus Toric Intraocular Lens Implantation During Cataract Surgery JEI HUN JEON, RIM HYUNG TAEK TYLER, KYOUNG YUL SEO, EUNG KWEON KIM, AND TAE-IM KIM PURPOSE: To compare refractive state changes in eyes implanted with toric intraocular lenses (IOLs) vs nontoric IOLs, after cataract extraction. DESIGN: Retrospective, comparative. METHODS: In a single institution, 121 eyes underwent phacoemulsification and implantation with either nontoric IOLs or toric IOLs. The spherical value, cylindrical value, spherical equivalent (SE) of refractive error, and visual acuity were measured preoperatively and 1, 3, and 6 months after surgery. Main outcome measures were the pattern of changes of spherical, cylindrical, and SE values based on postoperative time, between different IOL types. RESULTS: The groups, which included patients who underwent surgery with SN60WF (Group I), SA6AT3 (Group II-3), SA6AT4 (Group II-4), and SA6AT5 lenses (Group II-5), contained 37, 29, 23, and 32 eyes, respectively. The cylindrical value was significantly decreased in all groups (P < .05). Before surgery, the SE of refractive errors was estimated as L0.21, L0.10, L0.20, and L0.22 in the respective groups. The actual remaining SE values were L0.19, L0.24, L0.42, and L0.56 at 1 month; L0.17, L0.26, L0.57, and L0.64 at 3 months; and L0.17, L0.26, L0.70, and L0.74 at 6 months postoperatively, respectively. The follow-up SE values in groups I and II-3 were similar (P > .05 in both groups); however, significant myopic changes were observed in Groups II-4 and II-5 after surgery, vs Group I (P < .05). CONCLUSION: Selection of toric IOLs for cataract surgery requires a refined formula to precisely determine necessary IOL power, especially in cases with high levels of astigmatism, to reliably and accurately prevent myopic outcomes. (Am J Ophthalmol 2014;157:658–665. Ó 2014 by Elsevier Inc. All rights reserved.)
M
ODERN CATARACT SURGERY HAS CHANGED
from the simple surgical removal of lens opacity to providing patients the best possible vision. Also, modern cataract surgery employs concepts of
Accepted for publication Dec 2, 2013. From the Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea. Inquiries to Tae-im Kim, Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, 120-752, Seoul, South Korea; e-mail: [email protected]
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refractive surgery that can render patients free from glasses or contact lenses.1,2 Based on 1 report, 36.04% of 23 239 cataract eyes had astigmatism greater than 1 diopter (D), 8.09% were >2 D, and 2.65% were >3 D.3 Patients who had a high degree of corneal astigmatism before cataract surgery needed glasses or contact lenses after surgery. For precise axial length measurement, appropriate intraocular lens (IOL) power calculation using appropriate specific formulas has been developed.4 Also, various surgical techniques including small corneal incisions, foldable IOLs, and advanced phacoemulsification devices have been developed for minimizing surgically induced astigmatism.5–7 Although these methods can minimize surgically induced astigmatism, they do not effectively correct high degrees of preexisting astigmatism.8 To overcome this limitation, toric IOLs were developed to precisely correct astigmatism.9 For determining toric IOL power, the eye is examined and the proper IOL power is calculated using IOLMaster and A-scan parameters. Toricity (cylindrical power) of the toric lens alignment axis is calculated using a program available from the IOL manufacturer, using keratometry values measured by manual keratometry, IOLMaster, automated keratometry, or several kinds of corneal topographic analyses. Therefore, no consideration exists regarding the interaction between astigmatism correction and IOL lens power determination except for the specialized design for refractive adjustment of toric IOLs. Recently, investigators found that the refractive status of patients who received cataract extraction surgery with toric IOL implantation show greater myopia than expected preoperatively. Despite advanced techniques for analyzing corneal astigmatism and IOL power calculation, refractive power estimation for toric IOLs remains inaccurate. Therefore, we investigated the differences between the predicted spherical equivalent and the actual remnant spherical equivalent in patients who underwent cataract surgery with non-toric IOL vs toric IOL implantation.
METHODS PATIENTS:
This retrospective case-control study included a total of 121 eyes that underwent phacoemulsification and implantation with either a non-toric IOL
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TABLE 1. Demographics With Preoperative and Postoperative Mean Corneal Astigmatism, Spherical Error, Cylindrical Error, Spherical Equivalents, and Best-Corrected Visual Acuity in Non-toric and Toric Intraocular Lens Implantation IOL Type
Lens type Number of eyes Demographics Female, % Mean age, y Left eye, % Goal diopter (D)a Preoperative Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b BCVA (logMAR) 1 month postoperative Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b Deviation from the anticipated spherical equivalent BCVA (logMAR) 3 months postoperative Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b Deviation from the anticipated spherical equivalent BCVA (logMAR) 6 months postoperative Patients retained, n Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b Deviation from the anticipated spherical equivalent BCVA (logMAR)
Group I
Group II-3
Group II-4
Group II-5
Total
SN60WF 37
SA6AT3 29
SA6AT4 23
SA6AT5 32
62.2 66.8 54.1 0.21
55.2 67.3 31.0 0.10
52.2 64.3 43.5 0.20
62.5 61.9 62.5 0.22
58.7 65.2 48.8 0.19
42.76 43.68 0.92 0.54 1.20 105 1.14 0.3
43.61 45.24 1.63 0.38 1.78 87 0.51 0.3
43.01 45.03 2.01 3.21 2.75 88 4.59 0.4
43.05 45.74 2.69 1.11 2.93 119 2.58 0.3
43.17 44.91 1.74 0.98 2.09 101 2.03 0.3
42.87 43.68 0.81 0.16 0.71 89 0.19 0.02
43.67 45.00 1.33 0.15 0.79 80 0.24 0.14
43.10 44.74 1.64 0.01 0.86 100 0.42 0.22
43.18 45.69 2.51 0.04 1.03 61 0.56 0.34
43.25 44.81 1.56 0.08 0.84 82 0.34 0.15
0.0
0.1
0.1
0.1
0.1
43.02 43.89 0.87 0.22 0.77 93 0.17 0.04
44.10 45.35 1.25 0.07 0.68 83 0.26 0.16
43.10 44.87 1.77 0.12 0.91 88 0.57 0.37
43.35 45.88 2.53 0.14 1.00 76 0.64 0.42
43.40 44.70 1.30 0.02 0.83 85 0.39 0.20
0.0
0.1
0.1
0.0
0.1
30 42.92 43.72 0.80 0.21 0.77 97 0.17 0.01
16 44.09 45.52 1.43 0.13 0.78 94 0.26 0.16
17 43.24 44.87 1.63 0.27 0.86 82 0.70 0.52
25 43.11 45.72 2.61 0.17 1.15 65 0.74 0.50
88 43.20 44.82 1.62 0.00 0.90 84 0.45 0.26
0.0
0.0
0.1
0.0
0.0
121
BCVA ¼ best-corrected visual acuity; IOL ¼ intraocular lens. a Biometry was performed with optical coherence biometry (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA) using the SRK-T formula for the IOL power calculation. The target postoperative spherical equivalent was the nearest negative emmetropic value. b Spherical error þ cylindrical error/2.
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(Group I, Acrysof IQ SN60WF; Alcon Laboratories, Fort Worth, Texas, USA; n ¼ 37 eyes) or SA6AT3 (Group II-3, n ¼ 29 eyes), SA6AT4 (Group II-4, n ¼ 23 eyes), or SA6AT5 lens (Group II-5, n ¼ 32 eyes) (AcrySof Toric IOL; Alcon Laboratories) at Severance Hospital, Yonsei University, between January 11, 2008 and June 11, 2012. Uncorrected visual acuity, best-corrected visual acuity (BCVA), and refractive error were measured before surgery and 1, 3, and 6 months postoperatively. To examine refractive error, automated keratometry (KR-7100; Topcon, Tokyo, Japan) was used. Enrolled patients were 40-84 years old, with axial lengths of 22-25 mm and a range of IOL power of þ18 to þ24 D. Patients with previous glaucoma, amblyopia, irregular astigmatism, tear film or pupillary abnormalities, or optic nerve, corneal, or retinal disease were excluded. Patients who underwent previous refractive or intraocular surgery were also excluded. If intraoperative complications developed, such as vitreous loss, anterior chamber hyphema, uncontrollable postoperative intraocular pressure, zonular damage, capsulorrhexis tear, capsular rupture, or inability to place the optic and both haptics of the IOL into the capsular bag, these data were excluded. The Institutional Review Board of Yonsei University College of Medicine approved the retrospective review of patient data used in this study (No. 4-2013-0169), and the study adhered to the tenets of the Declaration of Helsinki.
Spherical Error 10 0.460 0.218 0.247
0.854 0.478 0.489
0.076 0.016 0.012
0.403 0.399 0.303
5
0 0.463 0.854
0.696 0.877
0.048 0.937
0.147 0.694
0.977
0.488
0.079
0.133
-5
-10 Group I
Group II-3 Group II-4 Group II-5 Postoperative 3M Postoperative 6M
Preoperative Postoperative 1M
Cylindrical Error 2
<0.001 <0.001 <0.001
<0.001 <0.001 <0.001
0.016 0.003 0.001
0.009 <0.001 <0.001
0.380 0.557
0.264 0.723
0.500 0.915
0.610 0.353
0.039
0.231
0.678
0.970
0
-2
-4
INTRAOCULAR LENSES:
-6
-8 Group I
Group II-3 Group II-4 Group II-5
Preoperative Postoperative 1M
Postoperative 3M Postoperative 6M
Spherical Equivalent 5 0.008 <0.001 0.001
0.735 0.305 0.758
0.177 0.076 0.173
0.072 0.002 0.004
0.838 0.573
0.700 0.877
0.074 0.756
0.111 0.845
0.284
0.698
0.020
0.153
0
-5
-10
-15 Group I
Group II-3
Preoperative Postoperative 1M
660
Group II-4
Postoperative 3M Postoperative 6M Goal diopter
Group II-5
The AcrySof Toric IOL is based on a similar single-piece platform as the non-toric AcrySof SN60AT IOL (Alcon Laboratories) except for asphericity, which is detailed below. The toric IOL has open-loop modified L-haptics with 3 reference dots on each side that mark the axis of the cylinder on its posterior surface.10 AcrySof SN60AT and Acrysof IQ SN60WF IOLs share the same physical qualities; both filter ultraviolet and blue light and are single-piece IOLs made of hydrophobic acrylic material with a refractive index of 1.55, a 6-mm square-edged biconvex optic, and a 13-mm overall length. The AcrySof IQ SN60WF additionally has an aspheric posterior optic design with a thinner posterior center, resulting in negative spherical aberration.11 Biometry was performed with optical coherence biometry (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA) using the SRK/T (Sanders-Retzlaff-Kraff/ Theoretical) formula for the IOL power calculation. The target postoperative spherical equivalent was the nearest
FIGURE 1. Individual changes in refractive errors (spherical error, cylindrical error, and spherical equivalent) during the 6-month follow-up in each IOL group after cataract surgery and implantation of either non-toric (Group I) or toric (Group II) IOLs. To determine the individual change in refractive errors, the Wilcoxon matched-pairs signed rank test was used. (Top) Spherical error; (Middle) cylindrical error; (Bottom) spherical equivalent. Bolded values highlight that P < .05.
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Spherical Error 0.002
0.076
0.040
0.037
0.165 0.687
0.001
0.170
0.335
2
2
2
1
1
1
0
0
0
-1
-1
-1
0.459
-2
0.911
0.437
-2
0.316
Group
I
0.830
0.041
-2
0.323
II-3 II-4 II-5
I
Postoperative 1M
0.424 0.382
II-3 II-4 II-5
II-3 II-4 II-5
I
Postoperative 3M
Postoperative 6M
Cylindrical Error 0.107
0.569
0.292
0.208
0.362
0.621
0.354
0.372
0
0
-.5
-.5
-1
-1
-1.5
-1.5
0.871
0
-.5
-1
-1.5 -2
0.534
0.606
-2
0.135
0.279
Group
I
0.738
0.394
0.214
II-3 II-4 II-5
I
Postoperative 1M
0.796 0.277
II-3 II-4 II-5
I
Postoperative 3M
II-3 II-4 II-5
Postoperative 6M
Spherical Equivalent 0.026
0.006
0.004
0.565
0.001
1
1
0
0
0
-1
-1
-1
0.140
0.791
-2
0.080
I
II-3 II-4 II-5
Postoperative 1M
0.694
-2
0.038
0.029
0.049
Group
I
0.001
0.344
1
-2
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<0.001
0.249
II-3 II-4 II-5
Postoperative 3M
0.928 0.052
I
II-3 II-4 II-5
Postoperative 6M
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negative emmetropic value. Intraocular lens cylinder power and the alignment axis were calculated using a program available from Alcon Laboratories (www.acrysoftoriccalculator. com). Surgical induced astigmatism was used as 0.5 on both eyes. Keratometry values were obtained by manual keratometry, IOLMaster keratometry, the Auto RefKeratometer, and a Pentacam rotating Scheimpflug imaging device (the last 2 devices were from Oculus Optikgera¨te GmbH, Wetzlar, Germany). The final keratometry value was chosen based on the data of manual ketatometry after checking the consistency of other values. If there were differences between manual keratometry with other values, we repeated each test and confirmed the consistency with the manual keratometric value. No significant difference between manual keratometric value and other values was found for any case. The toricity of toric IOLs was determined by an experienced surgeon based on recommended keratometric values, using the manufacturer-recommended program to assess data generated with the above methods.
and 6 months postoperatively. To assess astigmatism improvement after surgery, cylindrical errors at 1, 3, and 6 months after surgery were compared to the preoperative reference cylinder value. To assess the change in spherical equivalent after surgery, we compared the spherical equivalent at 1, 3, and 6 months after surgery with the preoperatively predicted goal diopter. To analyze individual changes in refractive error, the Wilcoxon matched-pairs signed rank test was used. We used the Mann-Whitney U test for comparing the refractive errors (spherical, cylinder, and spherical equivalent) between non-toric IOLs and toric IOLs at 1, 3, and 6 months after surgery. All statistical tests were 2-sided and were performed with Stata/SE version 12.1 software (StataCorp, College Station, Texas, USA).
SURGICAL TECHNIQUE:
THE GROUPS THAT RECEIVED NON-TORIC IOLS (GROUP I)
In Group II (II-3, II-4, and II-5), limbal reference marks were made before surgery at the 3-o’clock and 9-o’clock meridians under a slit lamp using a horizontal slit beam, with the patient sitting upright. In Group I and II after topical anesthesia with proparacaine hydrochloride 0.5% eye drops, the surgeon made a 2.70mm clear corneal incision on the steep axis. First, a continuous curvilinear capsulorrhexis measuring 5.5 mm in diameter was generated using a 26G bent needle, after an ophthalmic viscosurgical device (OVD) was inserted into the anterior chamber. After hydrodissection, phacoemulsification of the nucleus and aspiration of the residual cortex were conducted. After the lens capsule was inflated with the OVD, the IOL was injected into the capsular bag. Irrigation and aspiration were performed to minimize OVD retention. For toric IOL implantation in Group II, before IOL injection, the surgeon marked the alignment axis using an angular graduation instrument. After the IOL was injected into the capsular bag, gross alignment was achieved by rotating the IOL clockwise while it was unfolding, until it was placed 20-30 degrees short of the desired final position. After the OVD was removed, the IOL was rotated to its final position by exact alignment with the reference marks on the toric IOL with the alignment axis marks. Finally, a balanced salt solution was injected into the incision site to close the incision, causing edema. STATISTICAL METHODS:
We compared the change in refractive error between 1 and 3 months and between 3
RESULTS and toric IOLs (Groups II-3, II-4, and II-5) included 37, 29, 23, and 32 eyes, respectively. At 6 months after surgery, because of follow-up loss, only 30, 16, 17, and 30 eyes were examined in the respective groups. The mean BCVA of the respective groups was 0.3, 0.3, 0.4, and 0.3 (logMAR) preoperatively, which improved postoperatively after 1 month (0.0, 0.1, 0.1, 0.1), 3 months (0.0, 0.1, 0.1, 0.0), and 6 months (0.0, 0.0, 0.1, 0.0; Table 1). Preoperative spherical error values were significantly different in Group II-4 vs all other groups, and the remaining groups were not different from one another. A significant change during follow-up occurred only in Group II-4. This group had a significant change between 1 and 3 months after surgery (0.01 to 0.12, P < .040). After surgery, cylindrical errors significantly decreased in all groups compared with their respective preoperative values and did not change significantly during follow-up. Before surgery, estimated remaining refractive errors (goal diopters) were 0.21, 0.10, 0.20, and 0.22 in Groups I, II-3, II-4, and II-5, respectively. Actual remaining refractive errors were 0.19, 0.24, 042, and 0.56 at 1 month after surgery; 0.17, 0.26, 0.57, and 0.64 at 3 months; and 0.17, 0.26, 0.70, and 0.74 at 6 months, respectively. In Groups I and II-3, goal diopter and postoperative spherical equivalent were similarly improved (P > 0.05); however, in Groups II-4 and II-5 significant myopic spherical equivalents remained through 6 months of follow-up (P < 0.05) (Table 1, Figure 1).
FIGURE 2. Differences in refractive errors (spherical error, cylindrical error, and spherical equivalent) between non-toric (Group I) and toric (Group II) IOLs. The Mann-Whitney U test was used to compare the refractive errors between groups through 6 months of follow-up after cataract surgery and implantation of either non-toric (Group I) or toric (Group II) IOLs. (Top) Spherical error; (Middle) cylindrical error; (Bottom) spherical equivalent. Bolded values highlight that P < .05.
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TABLE 2. Comparison of Goal Diopter/Actual Spherical Equivalent Gap Size at Each Follow-up Point Among Patients Receiving Non-toric and Toric Intraocular Lenses
Goal dioptera Mean (6 SD) Spherical equivalentb 1 month postoperative Mean (6 SD) Median 3 months postoperative Mean (6 SD) Median 6 months postoperative Mean (6 SD) Median Deviation from the anticipated spherical equivalent Mean (6 SD) 1 month postoperative vs Group I (P value) 3 months postoperative vs Group I (P value) 6 months postoperative vs Group I (P value)
Group I
Group II-3
Group II-4
Group II-5
0.21 (0.17)
0.10 (0.08)
0.20 (0.13)
0.22 (0.22)
0.19 (0.40) 0.19
0.24 (0.54) 0.25
0.42 (0.57) 0.50
0.56 (0.55) 0.50
0.17 (0.38) 0.25
0.26 (0.60) 0.31
0.57 (0.50) 0.56
0.64 (0.49) 0.65
0.17 (0.38) 0.16
0.26 (0.55) 0.22
0.70 (0.55) 0.69
0.74 (0.66) 0.70
0.02 (0.40)
0.14 (0.57) .167 0.16 (0.61) .027 0.16 (0.56) .131
0.22 (0.57) .055 0.37 (0.48) .002 0.52 (0.54) .002
0.34 (0.57) .008 0.42 (0.50) .001 0.50 (0.62) .002
0.04 (0.39) 0.01 (0.38)
The Mann-Whitney U test was done to compare the non-toric group with toric groups. Bolded values highlight that P < .05. Biometry was performed with optical coherence biometry (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA) using the SRK-T formula for the IOL power calculation. The target postoperative spherical equivalent was the nearest negative emmetropic value. b Spherical error þ cylindrical error/2. a
Intergroup differences in spherical error, cylindrical error, and spherical equivalent were analyzed. Spherical error was significantly different between Group I and Groups II-4 and II-5, but not compared to Group II-3. Also, no significant differences were found in the remaining astigmatism at any follow-up times. Spherical equivalents were similar between Group I and Group II-3 at all time points. However, in Groups II-4 and II-5, postoperative refractive outcomes showed significantly greater myopia than Group I (Figure 2). In Table 2, the differences between goal diopter and spherical equivalent were analyzed and are presented at all followup points. Compared to non-toric Group I, Group II-3 had a significantly increased spherical equivalent/goal diopter gap at 3 months postoperatively (P ¼ .027). However, Group II-4 had a significantly increased gap at 3 and 6 months postoperatively vs Group I (P ¼ .002 at both time points), and Group II-5 had a significantly increased gap at 1, 3, and 6 months postoperatively (P ¼ .008, P < .001, and P ¼ .002).
DISCUSSION SEVERAL REPORTS HAVE BEEN PUBLISHED DESCRIBING THE
clinical outcome of toric IOL implantation after cataract VOL. 157, NO. 3
extraction. However, these studies mainly dealt with astigmatism change or rotation stability. Two studies stated that cataract surgery using toric IOL can correct astigmatism effectively.12,13 A different study showed that acrylic toric IOL had more rotational stability than silicone toric IOL.14 Based on an exhaustive PubMed search performed on July 19, 2013, this is the first study to evaluate refractive outcomes with respect to myopic spherical equivalent after toric IOL implantation. According to previous reports, cataract surgery may significantly reduce astigmatism using not only toric IOL implantation but also non-toric IOL implants. In our study, the astigmatism remaining in the non-toric IOL group after surgery was significantly less than preoperative astigmatism. Also, no significant difference was found between the non-toric IOL group and the toric IOL groups through 6 months of follow-up. These data suggest that astigmatism can be reduced by making clear corneal incisions only. Several previous reports about astigmatism change after surgery have been published. Small corneal incisions result in less astigmatism than large corneal incisions.15,16 Additionally, some studies showed that small degrees of astigmatism can be corrected by corneal incision without toric IOL implantation.5,17,18 T3 IOLs correct astigmatism by approximately 1.5 D, T4 IOLs correct up to 2.25 D,
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and T5 to 3.0 D. Astigmatism less than 1 D can be corrected with non-toric IOLs by adding a steep-axis corneal incision.5 A previous report with 120 eyes revealed that adding an opposite clear corneal incision on the steep meridian significantly decreases astigmatism more than a steep meridian incision alone.17 Also, a 3.2-mm steep-axis corneal incision decreased astigmatism 0.85 6 0.75 D, and paired opposite clear corneal incisions on the steep axis decreased astigmatism 1.66 6 0.5 D.18 Spherical equivalents after implanting high-toricity IOLs (Groups II-4 and II-5) were significantly different from preoperatively estimated goal diopters. Myopic refractive outcomes after cataract surgery have been studied by many researchers. Silicone IOLs (AQ 110 NV, 3-piece IOL), but not heparin-surface-modified polymethyl methacrylate or acrylic IOLs, shift anteriorly, resulting in myopic changes after cataract surgery. In those studies, a significant myopic change of spherical equivalent occurred beginning 2 months after surgery and was 0.33 6 0.59 D vs the immediate postoperative value. Also, myopic change continued throughout the follow-up period.19,20 Compared to previous reports, in our study hydrophobic acrylic IOLs were used, and no significant change was found in the spherical equivalent between the follow-up time points. Also, in Groups II-4 and II-5, the spherical equivalent was significantly different from the expected goal diopter calculated before surgery as early as 1 month after surgery. With these results, we may assume that the myopic increase was not caused by anterior shifting of the IOL. Moreover, the goal diopter/actually acquired spherical equivalent gap was significantly larger in the toric vs non-toric IOL groups, and this difference, though not reaching statistical significance, tended to be larger in Group II-5 than in Group II-4. Therefore, we may consider that preoperative IOL power calculations were not equally applied for determining IOL power in Groups II-4 and II-5. Group II-3 had a relatively low level of preoperative astigmatism and received lower-toricity IOLs. This resulted in no significant difference between the estimated goal
diopter and spherical equivalents after surgery. A remaining astigmatism may affect postoperative spherical equivalent; however, between groups, these were not significantly different. The Alcon toric calculator suggests the lowest T value of toric IOL that reduces the cylindrical error, avoiding a shift on the axis of astigmatism. The cylindrical value remained constant after surgery. To minimize the refractive error of spherical equivalent we chose the IOL power with the nearest negative emmetropic value in spherical equivalent. However, in Group II-4 and Group II-5, postoperative spherical error and cylindrical error are shown more myopic value than we expected. Therefore, negative spherical equivalent may result. In this study, a greater toricity of toric IOL caused a larger gap between the goal diopter and actual spherical equivalent errors. The SRK/T formula is based on preoperative keratometry values and axial length. However, IOL toricity and the amount of cylindrical error change are not considered as variables in this formula. We think that correction of cylindrical power can affect the final refractive state and calculation of IOL power. If the effect of toricity is not considered for IOL power calculations, the estimated goal diopter may not be accurate. Our relatively small sample size is a limitation of this study. If the sample size were larger, a significant difference and correlation between degree of astigmatism correction and myopic result in Group II-3 could have resulted. In addition, the value of postoperative anterior chamber depth was not evaluated in this study. Therefore, we could not investigate if changes to anterior chamber depth affected postoperative myopic refractive errors. In conclusion, high-toricity IOLs result in a more myopic surgical outcome than that in preoperative estimations. Therefore, we suggest an adjustment of 0.2 D lower IOL power than the calculated goal diopter for AcrySof toric T4 IOL and 0.3 D for AcrySof toric T5 IOL. Ultimately, a modified or novel formula that considers the effect of toricity on IOL refractive power is required for proper IOL power selection of implants used in cataract surgery.
ALL AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE FORM FOR DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST and none were reported. This work was partially supported by the National Research Foundation of South Korea (NRF) grant funded by the South Korea government [Ministry of Education, Science and Technology (MEST) No. 2013R1A1A2058907] and by the Converging Research Center Program through the Ministry of Science, Information and Communication Technologies (ICT) and Future Planning, South Korea (2013K000365). Contributions of authors: design of study (T.I.K.); conduct of study (J.H.J., T.I.K.); collection (J.H.J., T.I.K.), management (K.Y.S., E.K.K., T.I.K.), analysis (J.H.J., H.T.R., T.I.K.), and interpretation of data (J.H.J., T.I.K.); preparation of the manuscript (J.H.J., T.I.K.); and review and approval of manuscript (K.Y.S., E.K.K., T.I.K.). All authors had full access to all the data in the study and take responsibility for the integrity of the data and accuracy of the data analysis.
REFERENCES 1. Holladay JT, Piers PA, Koranyi G, van der Mooren M, Norrby NE. A new intraocular lens design to reduce spherical aberration of pseudophakic eyes. J Refract Surg 2002;18(6):683–691. 2. Werner L, Olson RJ, Mamalis N. New technology IOL optics. Ophthalmol Clin North Am 2006;19(4):469–483.
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3. Hoffmann PC, Hutz WW. Analysis of biometry and prevalence data for corneal astigmatism in 23,239 eyes. J Cataract Refract Surg 2010;36(9):1479–1485. 4. Olsen T. Calculation of intraocular lens power: a review. Acta Ophthalmol Scand 2007;85(5):472–485. 5. Amesbury EC, Miller KM. Correction of astigmatism at the time of cataract surgery. Curr Opin Ophthalmol 2009;20(1):19–24.
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6. Gills JP. Treating astigmatism at the time of cataract surgery. Curr Opin Ophthalmol 2002;13(1):2–6. 7. Nichamin LD. Treating astigmatism at the time of cataract surgery. Curr Opin Ophthalmol 2003;14(1):35–38. 8. Horn JD. Status of toric intraocular lenses. Curr Opin Ophthalmol 2007;18(1):58–61. 9. Mendicute J, Irigoyen C, Aramberri J, Ondarra A, MontesMico R. Foldable toric intraocular lens for astigmatism correction in cataract patients. J Cataract Refract Surg 2008; 34(4):601–607. 10. Bauer NJ, de Vries NE, Webers CA, Hendrikse F, Nuijts RM. Astigmatism management in cataract surgery with the AcrySof toric intraocular lens. J Cataract Refract Surg 2008;34(9): 1483–1488. 11. Awwad ST, Warmerdam D, Bowman RW, Dwarakanathan S, Cavanagh HD, McCulley JP. Contrast sensitivity and higher order aberrations in eyes implanted with AcrySof IQ SN60WF and AcrySof SN60AT intraocular lenses. J Refract Surg 2008;24(6):619–625. 12. Swiatek B, Michalska-Malecka K, Dorecka M, Romaniuk D, Romaniuk W. Results of the AcrySof Toric intraocular lenses implantation. Med Sci Monit 2012;18(1): PI1–PI4. 13. Till JS, Yoder PR Jr, Wilcox TK, Spielman JL. Toric intraocular lens implantation: 100 consecutive cases. J Cataract Refract Surg 2002;28(2):295–301.
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14. Chua WH, Yuen LH, Chua J, Teh G, Hill WE. Matched comparison of rotational stability of 1-piece acrylic and plate-haptic silicone toric intraocular lenses in Asian eyes. J Cataract Refract Surg 2012;38(4):620–624. 15. Alio J, Rodriguez-Prats JL, Galal A, Ramzy M. Outcomes of microincision cataract surgery versus coaxial phacoemulsification. Ophthalmology 2005;112(11):1997–2003. 16. Yao K, Tang X, Ye P. Corneal astigmatism, high order aberrations, and optical quality after cataract surgery: microincision versus small incision. J Refract Surg 2006;22(9 Suppl): S1079–S1082. 17. Bazzazi N, Barazandeh B, Kashani M, Rasouli M. Opposite clear corneal incisions versus steep meridian incision phacoemulsification for correction of pre-existing astigmatism. J Ophthalmic Vis Res 2008;3(2):87–90. 18. Khokhar S, Lohiya P, Murugiesan V, Panda A. Corneal astigmatism correction with opposite clear corneal incisions or single clear corneal incision: comparative analysis. J Cataract Refract Surg 2006;32(9):1432–1437. 19. Iwase T. [Change in refraction and intraocular lens position after cataract surgery]. Nihon Ganka Gakkai Zasshi 2005; 109(1):12–18. 20. Iwase T, Tanaka N, Sugiyama K. Postoperative refraction changes in phacoemulsification cataract surgery with implantation of different types of intraocular lens. Eur J Ophthalmol 2008;18(3):371–376.
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Biosketch Jei Hun Jeon graduated from the Yonsei University College of Medicine, Seoul, South Korea, and then completed his internship at the same university. He trained at the Department of Ophthalmology of the same university. His main research interests are visual function, cataract, and refractive surgery.
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M
ODERN CATARACT SURGERY HAS CHANGED
from the simple surgical removal of lens opacity to providing patients the best possible vision. Also, modern cataract surgery employs concepts of
Accepted for publication Dec 2, 2013. From the Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea. Inquiries to Tae-im Kim, Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, 120-752, Seoul, South Korea; e-mail: [email protected]
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refractive surgery that can render patients free from glasses or contact lenses.1,2 Based on 1 report, 36.04% of 23 239 cataract eyes had astigmatism greater than 1 diopter (D), 8.09% were >2 D, and 2.65% were >3 D.3 Patients who had a high degree of corneal astigmatism before cataract surgery needed glasses or contact lenses after surgery. For precise axial length measurement, appropriate intraocular lens (IOL) power calculation using appropriate specific formulas has been developed.4 Also, various surgical techniques including small corneal incisions, foldable IOLs, and advanced phacoemulsification devices have been developed for minimizing surgically induced astigmatism.5–7 Although these methods can minimize surgically induced astigmatism, they do not effectively correct high degrees of preexisting astigmatism.8 To overcome this limitation, toric IOLs were developed to precisely correct astigmatism.9 For determining toric IOL power, the eye is examined and the proper IOL power is calculated using IOLMaster and A-scan parameters. Toricity (cylindrical power) of the toric lens alignment axis is calculated using a program available from the IOL manufacturer, using keratometry values measured by manual keratometry, IOLMaster, automated keratometry, or several kinds of corneal topographic analyses. Therefore, no consideration exists regarding the interaction between astigmatism correction and IOL lens power determination except for the specialized design for refractive adjustment of toric IOLs. Recently, investigators found that the refractive status of patients who received cataract extraction surgery with toric IOL implantation show greater myopia than expected preoperatively. Despite advanced techniques for analyzing corneal astigmatism and IOL power calculation, refractive power estimation for toric IOLs remains inaccurate. Therefore, we investigated the differences between the predicted spherical equivalent and the actual remnant spherical equivalent in patients who underwent cataract surgery with non-toric IOL vs toric IOL implantation.
METHODS PATIENTS:
This retrospective case-control study included a total of 121 eyes that underwent phacoemulsification and implantation with either a non-toric IOL
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RIGHTS RESERVED.
0002-9394/$36.00 http://dx.doi.org/10.1016/j.ajo.2013.12.003
TABLE 1. Demographics With Preoperative and Postoperative Mean Corneal Astigmatism, Spherical Error, Cylindrical Error, Spherical Equivalents, and Best-Corrected Visual Acuity in Non-toric and Toric Intraocular Lens Implantation IOL Type
Lens type Number of eyes Demographics Female, % Mean age, y Left eye, % Goal diopter (D)a Preoperative Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b BCVA (logMAR) 1 month postoperative Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b Deviation from the anticipated spherical equivalent BCVA (logMAR) 3 months postoperative Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b Deviation from the anticipated spherical equivalent BCVA (logMAR) 6 months postoperative Patients retained, n Flat K (D) Steep K (D) Corneal astigmatism (D) Ocular spherical error (D) Ocular cylinder error (D) Axis (8 ) Spherical equivalents (D)b Deviation from the anticipated spherical equivalent BCVA (logMAR)
Group I
Group II-3
Group II-4
Group II-5
Total
SN60WF 37
SA6AT3 29
SA6AT4 23
SA6AT5 32
62.2 66.8 54.1 0.21
55.2 67.3 31.0 0.10
52.2 64.3 43.5 0.20
62.5 61.9 62.5 0.22
58.7 65.2 48.8 0.19
42.76 43.68 0.92 0.54 1.20 105 1.14 0.3
43.61 45.24 1.63 0.38 1.78 87 0.51 0.3
43.01 45.03 2.01 3.21 2.75 88 4.59 0.4
43.05 45.74 2.69 1.11 2.93 119 2.58 0.3
43.17 44.91 1.74 0.98 2.09 101 2.03 0.3
42.87 43.68 0.81 0.16 0.71 89 0.19 0.02
43.67 45.00 1.33 0.15 0.79 80 0.24 0.14
43.10 44.74 1.64 0.01 0.86 100 0.42 0.22
43.18 45.69 2.51 0.04 1.03 61 0.56 0.34
43.25 44.81 1.56 0.08 0.84 82 0.34 0.15
0.0
0.1
0.1
0.1
0.1
43.02 43.89 0.87 0.22 0.77 93 0.17 0.04
44.10 45.35 1.25 0.07 0.68 83 0.26 0.16
43.10 44.87 1.77 0.12 0.91 88 0.57 0.37
43.35 45.88 2.53 0.14 1.00 76 0.64 0.42
43.40 44.70 1.30 0.02 0.83 85 0.39 0.20
0.0
0.1
0.1
0.0
0.1
30 42.92 43.72 0.80 0.21 0.77 97 0.17 0.01
16 44.09 45.52 1.43 0.13 0.78 94 0.26 0.16
17 43.24 44.87 1.63 0.27 0.86 82 0.70 0.52
25 43.11 45.72 2.61 0.17 1.15 65 0.74 0.50
88 43.20 44.82 1.62 0.00 0.90 84 0.45 0.26
0.0
0.0
0.1
0.0
0.0
121
BCVA ¼ best-corrected visual acuity; IOL ¼ intraocular lens. a Biometry was performed with optical coherence biometry (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA) using the SRK-T formula for the IOL power calculation. The target postoperative spherical equivalent was the nearest negative emmetropic value. b Spherical error þ cylindrical error/2.
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(Group I, Acrysof IQ SN60WF; Alcon Laboratories, Fort Worth, Texas, USA; n ¼ 37 eyes) or SA6AT3 (Group II-3, n ¼ 29 eyes), SA6AT4 (Group II-4, n ¼ 23 eyes), or SA6AT5 lens (Group II-5, n ¼ 32 eyes) (AcrySof Toric IOL; Alcon Laboratories) at Severance Hospital, Yonsei University, between January 11, 2008 and June 11, 2012. Uncorrected visual acuity, best-corrected visual acuity (BCVA), and refractive error were measured before surgery and 1, 3, and 6 months postoperatively. To examine refractive error, automated keratometry (KR-7100; Topcon, Tokyo, Japan) was used. Enrolled patients were 40-84 years old, with axial lengths of 22-25 mm and a range of IOL power of þ18 to þ24 D. Patients with previous glaucoma, amblyopia, irregular astigmatism, tear film or pupillary abnormalities, or optic nerve, corneal, or retinal disease were excluded. Patients who underwent previous refractive or intraocular surgery were also excluded. If intraoperative complications developed, such as vitreous loss, anterior chamber hyphema, uncontrollable postoperative intraocular pressure, zonular damage, capsulorrhexis tear, capsular rupture, or inability to place the optic and both haptics of the IOL into the capsular bag, these data were excluded. The Institutional Review Board of Yonsei University College of Medicine approved the retrospective review of patient data used in this study (No. 4-2013-0169), and the study adhered to the tenets of the Declaration of Helsinki.
Spherical Error 10 0.460 0.218 0.247
0.854 0.478 0.489
0.076 0.016 0.012
0.403 0.399 0.303
5
0 0.463 0.854
0.696 0.877
0.048 0.937
0.147 0.694
0.977
0.488
0.079
0.133
-5
-10 Group I
Group II-3 Group II-4 Group II-5 Postoperative 3M Postoperative 6M
Preoperative Postoperative 1M
Cylindrical Error 2
<0.001 <0.001 <0.001
<0.001 <0.001 <0.001
0.016 0.003 0.001
0.009 <0.001 <0.001
0.380 0.557
0.264 0.723
0.500 0.915
0.610 0.353
0.039
0.231
0.678
0.970
0
-2
-4
INTRAOCULAR LENSES:
-6
-8 Group I
Group II-3 Group II-4 Group II-5
Preoperative Postoperative 1M
Postoperative 3M Postoperative 6M
Spherical Equivalent 5 0.008 <0.001 0.001
0.735 0.305 0.758
0.177 0.076 0.173
0.072 0.002 0.004
0.838 0.573
0.700 0.877
0.074 0.756
0.111 0.845
0.284
0.698
0.020
0.153
0
-5
-10
-15 Group I
Group II-3
Preoperative Postoperative 1M
660
Group II-4
Postoperative 3M Postoperative 6M Goal diopter
Group II-5
The AcrySof Toric IOL is based on a similar single-piece platform as the non-toric AcrySof SN60AT IOL (Alcon Laboratories) except for asphericity, which is detailed below. The toric IOL has open-loop modified L-haptics with 3 reference dots on each side that mark the axis of the cylinder on its posterior surface.10 AcrySof SN60AT and Acrysof IQ SN60WF IOLs share the same physical qualities; both filter ultraviolet and blue light and are single-piece IOLs made of hydrophobic acrylic material with a refractive index of 1.55, a 6-mm square-edged biconvex optic, and a 13-mm overall length. The AcrySof IQ SN60WF additionally has an aspheric posterior optic design with a thinner posterior center, resulting in negative spherical aberration.11 Biometry was performed with optical coherence biometry (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA) using the SRK/T (Sanders-Retzlaff-Kraff/ Theoretical) formula for the IOL power calculation. The target postoperative spherical equivalent was the nearest
FIGURE 1. Individual changes in refractive errors (spherical error, cylindrical error, and spherical equivalent) during the 6-month follow-up in each IOL group after cataract surgery and implantation of either non-toric (Group I) or toric (Group II) IOLs. To determine the individual change in refractive errors, the Wilcoxon matched-pairs signed rank test was used. (Top) Spherical error; (Middle) cylindrical error; (Bottom) spherical equivalent. Bolded values highlight that P < .05.
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Spherical Error 0.002
0.076
0.040
0.037
0.165 0.687
0.001
0.170
0.335
2
2
2
1
1
1
0
0
0
-1
-1
-1
0.459
-2
0.911
0.437
-2
0.316
Group
I
0.830
0.041
-2
0.323
II-3 II-4 II-5
I
Postoperative 1M
0.424 0.382
II-3 II-4 II-5
II-3 II-4 II-5
I
Postoperative 3M
Postoperative 6M
Cylindrical Error 0.107
0.569
0.292
0.208
0.362
0.621
0.354
0.372
0
0
-.5
-.5
-1
-1
-1.5
-1.5
0.871
0
-.5
-1
-1.5 -2
0.534
0.606
-2
0.135
0.279
Group
I
0.738
0.394
0.214
II-3 II-4 II-5
I
Postoperative 1M
0.796 0.277
II-3 II-4 II-5
I
Postoperative 3M
II-3 II-4 II-5
Postoperative 6M
Spherical Equivalent 0.026
0.006
0.004
0.565
0.001
1
1
0
0
0
-1
-1
-1
0.140
0.791
-2
0.080
I
II-3 II-4 II-5
Postoperative 1M
0.694
-2
0.038
0.029
0.049
Group
I
0.001
0.344
1
-2
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<0.001
0.249
II-3 II-4 II-5
Postoperative 3M
0.928 0.052
I
II-3 II-4 II-5
Postoperative 6M
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negative emmetropic value. Intraocular lens cylinder power and the alignment axis were calculated using a program available from Alcon Laboratories (www.acrysoftoriccalculator. com). Surgical induced astigmatism was used as 0.5 on both eyes. Keratometry values were obtained by manual keratometry, IOLMaster keratometry, the Auto RefKeratometer, and a Pentacam rotating Scheimpflug imaging device (the last 2 devices were from Oculus Optikgera¨te GmbH, Wetzlar, Germany). The final keratometry value was chosen based on the data of manual ketatometry after checking the consistency of other values. If there were differences between manual keratometry with other values, we repeated each test and confirmed the consistency with the manual keratometric value. No significant difference between manual keratometric value and other values was found for any case. The toricity of toric IOLs was determined by an experienced surgeon based on recommended keratometric values, using the manufacturer-recommended program to assess data generated with the above methods.
and 6 months postoperatively. To assess astigmatism improvement after surgery, cylindrical errors at 1, 3, and 6 months after surgery were compared to the preoperative reference cylinder value. To assess the change in spherical equivalent after surgery, we compared the spherical equivalent at 1, 3, and 6 months after surgery with the preoperatively predicted goal diopter. To analyze individual changes in refractive error, the Wilcoxon matched-pairs signed rank test was used. We used the Mann-Whitney U test for comparing the refractive errors (spherical, cylinder, and spherical equivalent) between non-toric IOLs and toric IOLs at 1, 3, and 6 months after surgery. All statistical tests were 2-sided and were performed with Stata/SE version 12.1 software (StataCorp, College Station, Texas, USA).
SURGICAL TECHNIQUE:
THE GROUPS THAT RECEIVED NON-TORIC IOLS (GROUP I)
In Group II (II-3, II-4, and II-5), limbal reference marks were made before surgery at the 3-o’clock and 9-o’clock meridians under a slit lamp using a horizontal slit beam, with the patient sitting upright. In Group I and II after topical anesthesia with proparacaine hydrochloride 0.5% eye drops, the surgeon made a 2.70mm clear corneal incision on the steep axis. First, a continuous curvilinear capsulorrhexis measuring 5.5 mm in diameter was generated using a 26G bent needle, after an ophthalmic viscosurgical device (OVD) was inserted into the anterior chamber. After hydrodissection, phacoemulsification of the nucleus and aspiration of the residual cortex were conducted. After the lens capsule was inflated with the OVD, the IOL was injected into the capsular bag. Irrigation and aspiration were performed to minimize OVD retention. For toric IOL implantation in Group II, before IOL injection, the surgeon marked the alignment axis using an angular graduation instrument. After the IOL was injected into the capsular bag, gross alignment was achieved by rotating the IOL clockwise while it was unfolding, until it was placed 20-30 degrees short of the desired final position. After the OVD was removed, the IOL was rotated to its final position by exact alignment with the reference marks on the toric IOL with the alignment axis marks. Finally, a balanced salt solution was injected into the incision site to close the incision, causing edema. STATISTICAL METHODS:
We compared the change in refractive error between 1 and 3 months and between 3
RESULTS and toric IOLs (Groups II-3, II-4, and II-5) included 37, 29, 23, and 32 eyes, respectively. At 6 months after surgery, because of follow-up loss, only 30, 16, 17, and 30 eyes were examined in the respective groups. The mean BCVA of the respective groups was 0.3, 0.3, 0.4, and 0.3 (logMAR) preoperatively, which improved postoperatively after 1 month (0.0, 0.1, 0.1, 0.1), 3 months (0.0, 0.1, 0.1, 0.0), and 6 months (0.0, 0.0, 0.1, 0.0; Table 1). Preoperative spherical error values were significantly different in Group II-4 vs all other groups, and the remaining groups were not different from one another. A significant change during follow-up occurred only in Group II-4. This group had a significant change between 1 and 3 months after surgery (0.01 to 0.12, P < .040). After surgery, cylindrical errors significantly decreased in all groups compared with their respective preoperative values and did not change significantly during follow-up. Before surgery, estimated remaining refractive errors (goal diopters) were 0.21, 0.10, 0.20, and 0.22 in Groups I, II-3, II-4, and II-5, respectively. Actual remaining refractive errors were 0.19, 0.24, 042, and 0.56 at 1 month after surgery; 0.17, 0.26, 0.57, and 0.64 at 3 months; and 0.17, 0.26, 0.70, and 0.74 at 6 months, respectively. In Groups I and II-3, goal diopter and postoperative spherical equivalent were similarly improved (P > 0.05); however, in Groups II-4 and II-5 significant myopic spherical equivalents remained through 6 months of follow-up (P < 0.05) (Table 1, Figure 1).
FIGURE 2. Differences in refractive errors (spherical error, cylindrical error, and spherical equivalent) between non-toric (Group I) and toric (Group II) IOLs. The Mann-Whitney U test was used to compare the refractive errors between groups through 6 months of follow-up after cataract surgery and implantation of either non-toric (Group I) or toric (Group II) IOLs. (Top) Spherical error; (Middle) cylindrical error; (Bottom) spherical equivalent. Bolded values highlight that P < .05.
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TABLE 2. Comparison of Goal Diopter/Actual Spherical Equivalent Gap Size at Each Follow-up Point Among Patients Receiving Non-toric and Toric Intraocular Lenses
Goal dioptera Mean (6 SD) Spherical equivalentb 1 month postoperative Mean (6 SD) Median 3 months postoperative Mean (6 SD) Median 6 months postoperative Mean (6 SD) Median Deviation from the anticipated spherical equivalent Mean (6 SD) 1 month postoperative vs Group I (P value) 3 months postoperative vs Group I (P value) 6 months postoperative vs Group I (P value)
Group I
Group II-3
Group II-4
Group II-5
0.21 (0.17)
0.10 (0.08)
0.20 (0.13)
0.22 (0.22)
0.19 (0.40) 0.19
0.24 (0.54) 0.25
0.42 (0.57) 0.50
0.56 (0.55) 0.50
0.17 (0.38) 0.25
0.26 (0.60) 0.31
0.57 (0.50) 0.56
0.64 (0.49) 0.65
0.17 (0.38) 0.16
0.26 (0.55) 0.22
0.70 (0.55) 0.69
0.74 (0.66) 0.70
0.02 (0.40)
0.14 (0.57) .167 0.16 (0.61) .027 0.16 (0.56) .131
0.22 (0.57) .055 0.37 (0.48) .002 0.52 (0.54) .002
0.34 (0.57) .008 0.42 (0.50) .001 0.50 (0.62) .002
0.04 (0.39) 0.01 (0.38)
The Mann-Whitney U test was done to compare the non-toric group with toric groups. Bolded values highlight that P < .05. Biometry was performed with optical coherence biometry (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA) using the SRK-T formula for the IOL power calculation. The target postoperative spherical equivalent was the nearest negative emmetropic value. b Spherical error þ cylindrical error/2. a
Intergroup differences in spherical error, cylindrical error, and spherical equivalent were analyzed. Spherical error was significantly different between Group I and Groups II-4 and II-5, but not compared to Group II-3. Also, no significant differences were found in the remaining astigmatism at any follow-up times. Spherical equivalents were similar between Group I and Group II-3 at all time points. However, in Groups II-4 and II-5, postoperative refractive outcomes showed significantly greater myopia than Group I (Figure 2). In Table 2, the differences between goal diopter and spherical equivalent were analyzed and are presented at all followup points. Compared to non-toric Group I, Group II-3 had a significantly increased spherical equivalent/goal diopter gap at 3 months postoperatively (P ¼ .027). However, Group II-4 had a significantly increased gap at 3 and 6 months postoperatively vs Group I (P ¼ .002 at both time points), and Group II-5 had a significantly increased gap at 1, 3, and 6 months postoperatively (P ¼ .008, P < .001, and P ¼ .002).
DISCUSSION SEVERAL REPORTS HAVE BEEN PUBLISHED DESCRIBING THE
clinical outcome of toric IOL implantation after cataract VOL. 157, NO. 3
extraction. However, these studies mainly dealt with astigmatism change or rotation stability. Two studies stated that cataract surgery using toric IOL can correct astigmatism effectively.12,13 A different study showed that acrylic toric IOL had more rotational stability than silicone toric IOL.14 Based on an exhaustive PubMed search performed on July 19, 2013, this is the first study to evaluate refractive outcomes with respect to myopic spherical equivalent after toric IOL implantation. According to previous reports, cataract surgery may significantly reduce astigmatism using not only toric IOL implantation but also non-toric IOL implants. In our study, the astigmatism remaining in the non-toric IOL group after surgery was significantly less than preoperative astigmatism. Also, no significant difference was found between the non-toric IOL group and the toric IOL groups through 6 months of follow-up. These data suggest that astigmatism can be reduced by making clear corneal incisions only. Several previous reports about astigmatism change after surgery have been published. Small corneal incisions result in less astigmatism than large corneal incisions.15,16 Additionally, some studies showed that small degrees of astigmatism can be corrected by corneal incision without toric IOL implantation.5,17,18 T3 IOLs correct astigmatism by approximately 1.5 D, T4 IOLs correct up to 2.25 D,
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and T5 to 3.0 D. Astigmatism less than 1 D can be corrected with non-toric IOLs by adding a steep-axis corneal incision.5 A previous report with 120 eyes revealed that adding an opposite clear corneal incision on the steep meridian significantly decreases astigmatism more than a steep meridian incision alone.17 Also, a 3.2-mm steep-axis corneal incision decreased astigmatism 0.85 6 0.75 D, and paired opposite clear corneal incisions on the steep axis decreased astigmatism 1.66 6 0.5 D.18 Spherical equivalents after implanting high-toricity IOLs (Groups II-4 and II-5) were significantly different from preoperatively estimated goal diopters. Myopic refractive outcomes after cataract surgery have been studied by many researchers. Silicone IOLs (AQ 110 NV, 3-piece IOL), but not heparin-surface-modified polymethyl methacrylate or acrylic IOLs, shift anteriorly, resulting in myopic changes after cataract surgery. In those studies, a significant myopic change of spherical equivalent occurred beginning 2 months after surgery and was 0.33 6 0.59 D vs the immediate postoperative value. Also, myopic change continued throughout the follow-up period.19,20 Compared to previous reports, in our study hydrophobic acrylic IOLs were used, and no significant change was found in the spherical equivalent between the follow-up time points. Also, in Groups II-4 and II-5, the spherical equivalent was significantly different from the expected goal diopter calculated before surgery as early as 1 month after surgery. With these results, we may assume that the myopic increase was not caused by anterior shifting of the IOL. Moreover, the goal diopter/actually acquired spherical equivalent gap was significantly larger in the toric vs non-toric IOL groups, and this difference, though not reaching statistical significance, tended to be larger in Group II-5 than in Group II-4. Therefore, we may consider that preoperative IOL power calculations were not equally applied for determining IOL power in Groups II-4 and II-5. Group II-3 had a relatively low level of preoperative astigmatism and received lower-toricity IOLs. This resulted in no significant difference between the estimated goal
diopter and spherical equivalents after surgery. A remaining astigmatism may affect postoperative spherical equivalent; however, between groups, these were not significantly different. The Alcon toric calculator suggests the lowest T value of toric IOL that reduces the cylindrical error, avoiding a shift on the axis of astigmatism. The cylindrical value remained constant after surgery. To minimize the refractive error of spherical equivalent we chose the IOL power with the nearest negative emmetropic value in spherical equivalent. However, in Group II-4 and Group II-5, postoperative spherical error and cylindrical error are shown more myopic value than we expected. Therefore, negative spherical equivalent may result. In this study, a greater toricity of toric IOL caused a larger gap between the goal diopter and actual spherical equivalent errors. The SRK/T formula is based on preoperative keratometry values and axial length. However, IOL toricity and the amount of cylindrical error change are not considered as variables in this formula. We think that correction of cylindrical power can affect the final refractive state and calculation of IOL power. If the effect of toricity is not considered for IOL power calculations, the estimated goal diopter may not be accurate. Our relatively small sample size is a limitation of this study. If the sample size were larger, a significant difference and correlation between degree of astigmatism correction and myopic result in Group II-3 could have resulted. In addition, the value of postoperative anterior chamber depth was not evaluated in this study. Therefore, we could not investigate if changes to anterior chamber depth affected postoperative myopic refractive errors. In conclusion, high-toricity IOLs result in a more myopic surgical outcome than that in preoperative estimations. Therefore, we suggest an adjustment of 0.2 D lower IOL power than the calculated goal diopter for AcrySof toric T4 IOL and 0.3 D for AcrySof toric T5 IOL. Ultimately, a modified or novel formula that considers the effect of toricity on IOL refractive power is required for proper IOL power selection of implants used in cataract surgery.
ALL AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE FORM FOR DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST and none were reported. This work was partially supported by the National Research Foundation of South Korea (NRF) grant funded by the South Korea government [Ministry of Education, Science and Technology (MEST) No. 2013R1A1A2058907] and by the Converging Research Center Program through the Ministry of Science, Information and Communication Technologies (ICT) and Future Planning, South Korea (2013K000365). Contributions of authors: design of study (T.I.K.); conduct of study (J.H.J., T.I.K.); collection (J.H.J., T.I.K.), management (K.Y.S., E.K.K., T.I.K.), analysis (J.H.J., H.T.R., T.I.K.), and interpretation of data (J.H.J., T.I.K.); preparation of the manuscript (J.H.J., T.I.K.); and review and approval of manuscript (K.Y.S., E.K.K., T.I.K.). All authors had full access to all the data in the study and take responsibility for the integrity of the data and accuracy of the data analysis.
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Biosketch Jei Hun Jeon graduated from the Yonsei University College of Medicine, Seoul, South Korea, and then completed his internship at the same university. He trained at the Department of Ophthalmology of the same university. His main research interests are visual function, cataract, and refractive surgery.
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