Purpose
To compare refractive state changes in eyes implanted with toric intraocular lenses (IOLs) vs non-toric IOLs, after cataract extraction.
Design
Retrospective, comparative.
Methods
In a single institution, 121 eyes underwent phacoemulsification and implantation with either non-toric 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 −0.21, −0.10, −0.20, and −0.22 in the respective groups. The actual remaining SE values were −0.19, −0.24, −0.42, and −0.56 at 1 month; −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 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.
Modern 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 refractive surgery that can render patients free from glasses or contact lenses.
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. 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. Also, various surgical techniques including small corneal incisions, foldable IOLs, and advanced phacoemulsification devices have been developed for minimizing surgically induced astigmatism. Although these methods can minimize surgically induced astigmatism, they do not effectively correct high degrees of preexisting astigmatism. To overcome this limitation, toric IOLs were developed to precisely correct astigmatism.
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 (Group I, Acrysof IQ SN60WF; Alcon Laboratories, Fort Worth, Texas, USA; n = 37 eyes) or SA6AT3 (Group II-3, n = 29 eyes), SA6AT4 (Group II-4, n = 23 eyes), or SA6AT5 lens (Group II-5, n = 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 +18 to +24 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.
Intraocular Lenses
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. 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. 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 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 Ref-Keratometer, and a Pentacam rotating Scheimpflug imaging device (the last 2 devices were from Oculus Optikgeräte 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.
Surgical Technique
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 2.70-mm 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 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).
Results
The groups that received non-toric IOLs (Group I) 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 ).
| IOL Type | Total | ||||
|---|---|---|---|---|---|
| Group I | Group II-3 | Group II-4 | Group II-5 | ||
| Lens type | SN60WF | SA6AT3 | SA6AT4 | SA6AT5 | |
| Number of eyes | 37 | 29 | 23 | 32 | 121 |
| Demographics | |||||
| Female, % | 62.2 | 55.2 | 52.2 | 62.5 | 58.7 |
| Mean age, y | 66.8 | 67.3 | 64.3 | 61.9 | 65.2 |
| Left eye, % | 54.1 | 31.0 | 43.5 | 62.5 | 48.8 |
| Goal diopter (D) a | −0.21 | −0.10 | −0.20 | −0.22 | −0.19 |
| Preoperative | |||||
| Flat K (D) | 42.76 | 43.61 | 43.01 | 43.05 | 43.17 |
| Steep K (D) | 43.68 | 45.24 | 45.03 | 45.74 | 44.91 |
| Corneal astigmatism (D) | 0.92 | 1.63 | 2.01 | 2.69 | 1.74 |
| Ocular spherical error (D) | −0.54 | 0.38 | −3.21 | −1.11 | −0.98 |
| Ocular cylinder error (D) | −1.20 | −1.78 | −2.75 | −2.93 | −2.09 |
| Axis (°) | 105 | 87 | 88 | 119 | 101 |
| Spherical equivalents (D) b | −1.14 | −0.51 | −4.59 | −2.58 | −2.03 |
| BCVA (logMAR) | 0.3 | 0.3 | 0.4 | 0.3 | 0.3 |
| 1 month postoperative | |||||
| Flat K (D) | 42.87 | 43.67 | 43.10 | 43.18 | 43.25 |
| Steep K (D) | 43.68 | 45.00 | 44.74 | 45.69 | 44.81 |
| Corneal astigmatism (D) | 0.81 | 1.33 | 1.64 | 2.51 | 1.56 |
| Ocular spherical error (D) | 0.16 | 0.15 | 0.01 | −0.04 | 0.08 |
| Ocular cylinder error (D) | −0.71 | −0.79 | −0.86 | −1.03 | −0.84 |
| Axis (°) | 89 | 80 | 100 | 61 | 82 |
| Spherical equivalents (D) b | −0.19 | −0.24 | −0.42 | −0.56 | −0.34 |
| Deviation from the anticipated spherical equivalent | 0.02 | −0.14 | −0.22 | −0.34 | −0.15 |
| BCVA (logMAR) | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 |
| 3 months postoperative | |||||
| Flat K (D) | 43.02 | 44.10 | 43.10 | 43.35 | 43.40 |
| Steep K (D) | 43.89 | 45.35 | 44.87 | 45.88 | 44.70 |
| Corneal astigmatism (D) | 0.87 | 1.25 | 1.77 | 2.53 | 1.30 |
| Ocular spherical error (D) | 0.22 | 0.07 | −0.12 | −0.14 | 0.02 |
| Ocular cylinder error (D) | −0.77 | −0.68 | −0.91 | −1.00 | −0.83 |
| Axis (°) | 93 | 83 | 88 | 76 | 85 |
| Spherical equivalents (D) b | −0.17 | −0.26 | −0.57 | −0.64 | −0.39 |
| Deviation from the anticipated spherical equivalent | 0.04 | −0.16 | −0.37 | −0.42 | −0.20 |
| BCVA (logMAR) | 0.0 | 0.1 | 0.1 | 0.0 | 0.1 |
| 6 months postoperative | |||||
| Patients retained, n | 30 | 16 | 17 | 25 | 88 |
| Flat K (D) | 42.92 | 44.09 | 43.24 | 43.11 | 43.20 |
| Steep K (D) | 43.72 | 45.52 | 44.87 | 45.72 | 44.82 |
| Corneal astigmatism (D) | 0.80 | 1.43 | 1.63 | 2.61 | 1.62 |
| Ocular spherical error (D) | 0.21 | 0.13 | −0.27 | −0.17 | 0.00 |
| Ocular cylinder error (D) | −0.77 | −0.78 | −0.86 | −1.15 | −0.90 |
| Axis (°) | 97 | 94 | 82 | 65 | 84 |
| Spherical equivalents (D) b | −0.17 | −0.26 | −0.70 | −0.74 | −0.45 |
| Deviation from the anticipated spherical equivalent | 0.01 | −0.16 | −0.52 | −0.50 | −0.26 |
| BCVA (logMAR) | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 |
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.
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 ).
