ARTICLE
Vector analysis of astigmatism correction after toric intraocular lens implantation Eva M. Krall, MD, Eva M. Arlt, MD, Melchior Hohensinn, MD, Sarah Moussa, MD, Gerlinde Jell, MD, Jorge L. Ali o, MD, PhD, Ana B. Plaza-Puche, MD, MSc, Lucia Bascaran, MD, Javier Mendicute, MD, PhD, G€ unther Grabner, MD, Alois K. Dexl, MD, MSc
PURPOSE: To determine astigmatic changes by vector analysis and postoperative refractive and visual outcomes after implantation of the monofocal aspheric bitoric AT Torbi 709M toric intraocular lens (IOL). SETTING: Three centers in Salzburg, Austria, and Alicante and San Sebastian, Spain. DESIGN: Prospective interventional case series. METHODS: Preoperative and postoperative visual acuity, subjective and objective refractions, and corneal radii using a topographer were examined in all patients. All patients had postoperative examinations within the first week and at 6 to 12 weeks. Astigmatic changes were evaluated using the Alpins vector method based on 3 fundamental vectors as follows: target induced astigmatism (TIA), surgically induced astigmatism (SIA), and difference vector. The various relationships between these 3 vectors were calculated, providing an extensive description of the astigmatic correction achieved. RESULTS: Eighty-eight eyes (71 patients) were included. Postoperatively, refractive cylinder was reduced significantly (P < .001), concurrent with visual improvement. The mean magnitude of the SIA vector (2.54 diopters [D] G 1.21 [SD]) was slightly higher than the mean magnitude of the TIA vector (2.37 G 1.15 D) at the last follow-up. The mean difference vector was 0.46 G 0.46 D, the mean magnitude of error was 0.16 G 0.46 D, and the mean correction index was 1.09 G 0.21, all indicating minimal overcorrection at 3 months that remained stable during the follow-up. CONCLUSION: Implantation of the toric IOL was safe and effective for the treatment of eyes with cataract in combination with preexisting regular corneal astigmatism over a short-term follow-up. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:790–799 Q 2015 ASCRS and ESCRS
Modern cataract surgery offers the possibility of compensating for spherical and astigmatic refractive errors, thus providing enhanced visual rehabilitation. In a recent biometry study of 23 239 eyes,1 corneal astigmatism of 1.0 diopter (D) or more was observed in 28% of patients. Several techniques, including opposite clear corneal incisions,2 limbal relaxing incisions,3 femtosecond laser–assisted astigmatic keratotomy,4 excimer laser refractive procedures,5,6 and toric intraocular lens (IOL) implantation,7 are available to correct regular corneal astigmatism. The implantation of toric IOLs is an effective treatment of lens opacification and concomitant regular corneal astigmatism in a single surgical procedure and has been proven to be safe and predictable.8 790
Q 2015 ASCRS and ESCRS Published by Elsevier Inc.
To evaluate the efficacy of toric IOL implantation, astigmatic change can be determined by vector analysis considering its magnitude and axis. In brief, vector analysis determines a goal for astigmatism correction and a treatment required to achieve that goal. The method also allows the calculation of the principal components by which an operation fails to achieve its goal and other components that assist in comparing the results of astigmatism surgery in individuals and groups of individuals.9,10 The purpose of this study was to determine the astigmatic changes using vector analysis as well as postoperative refractive and visual outcomes within the first 3 months after implantation of the AT Torbi 709M toric IOL (Carl Zeiss Meditec AG). http://dx.doi.org/10.1016/j.jcrs.2014.07.038 0886-3350
VECTOR ANALYSIS AFTER TORIC IOL IMPLANTATION
PATIENTS AND METHODS Patient Population This clinical trial was designed as a prospective multicenter interventional case series with 3 participating ophthalmologic centers as follows: Vissum Corporation, Division of Ophthalmology, Universidad Miguel Hern andez, Alicante, Spain; Ophthalmology Service, Donostia Hospital, San Sebastian, Spain; and Department of Ophthalmology, Paracelsus Medical University, Salzburg, Austria. The study was performed in accordance with the tenets of the Declaration of Helsinki and approved by each center’s local institutional review board or ethics committee. After receiving a detailed explanation of the purpose, procedure, and patient responsibilities, all trial patients provided signed informed consent for participation in this study. Patients were eligible for inclusion if they were older than 40 years, had age-related cataract with regular corneal astigmatism without additional ocular pathology, had a stable corneal condition, and had refraction within the past 12 months. Exclusion criteria were irregular corneal astigmatism, serious intraoperative complications, glaucoma, pseudoexfoliation syndrome, uveitis, macular degeneration or other retinal impairment, corneal scarring, amblyopia with a corrected distance visual acuity less than 0.5, and a need for a toric IOL outside the available spherical range (10.0 to C32.0 D) and/or outside cylindrical range (1.0 to 12.0 D).
Preoperative Assessment Before surgery, a complete medical history was taken and all patients had a full ophthalmologic examination including refraction and uncorrected (UDVA) and corrected (CDVA) distance visual acuity measurements. The Early Treatment Diabetic Retinopathy Study charts at a test distance of 4 m were used by counting the numbers of optotypes the patient identified correctly and converting this number into logMAR
Submitted: April 3, 2014. Final revision submitted: July 5, 2014. Accepted: July 15, 2014. From the Department of Ophthalmology (Krall, Arlt, Hohensinn, Moussa, Jell, Grabner, Dexl), Paracelsus Medical University, Salzburg, Austria; the Division of Ophthalmology (Alio, Plaza-Puche), Vissum Corporation, Universidad Miguel Hernandez, Alicante, and the Ophthalmology Service (Bascaran, Mendicute), Donostia Hospital, San Sebastian, Spain. Supported by the Fuchs Foundation for the Promotion of Research in Ophthalmology, Salzburg, Austria. Carl Zeiss Meditec AG, Jena, Germany, financially supports the Fuchs Foundation as the clinical research center of the Department of Ophthalmology of the Paracelsus Medical University, Salzburg, Austria (grant 23-2011). Presented at the XXX Congress of the European Society of Cataract and Refractive Surgeons, Amsterdam, the Netherlands, October 2013. Corresponding author: Alois K. Dexl, MD, MSc, Department of Ophthalmology, Paracelsus Medical University, M€ ullner Hauptstraße 48, A-5020 Salzburg, Austria. E-mail: [email protected].
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values. Keratometric values were measured with partial coherence interferometry (PCI) (IOLMaster, Carl Zeiss Meditec AG) for IOL calculation, and corneal topography was performed to ensure regularity of the corneal astigmatism. Intraocular lens power calculation was performed using the online calculation program Z CALC (Carl Zeiss Meditec AG). This calculation program requires the input of the following PCI data: axial length, anterior chamber depth (ACD), keratometry values in diopters, and IOL type to be implanted.
Intraocular Lens The AT Torbi 709M is a monofocal bitoric aspheric IOL with an optic diameter of 6.0 mm and a total diameter of 11.0 mm. The optic design provides aberration-neutral convergent incidence of light.A The optic material of the IOL is foldable hydrophilic acrylate with a hydrophobic surface and 25% water content and an ultraviolet filter. The haptic angulation is 0 degrees, and the IOL is available in spherical ranges of 10.0 to C32.0 D in 0.5 D increments and in toric ranges of C1.0 to C12.0 D in 0.5 D increments.A
Surgical Technique One experienced surgeon (G.G., J.L.A., J.M.) performed all surgeries at each center using topical anesthesia. All patients were operated on with a standard sutureless phacoemulsification technique. In all cases, the IOL was implanted in the capsular bag with the single-use injector A6/AT. Smart Cartridge Set (Carl Zeiss Meditec AG), requiring an incision width of at least 1.8 mm. Surgical preparation, IOL implantation, postoperative treatment, and postoperative medication were performed/applied corresponding to the routine procedure of the respective center. At the Alicante facility, both the 0-degree axis and 180-degree axis were marked with a needle on the corneal epithelium with the patient seated at the slitlamp. The IOL was implanted in the axis corresponding to the calculation program, with the 180-degree premarked axis acting as a reference. After IOL implantation, all ophthalmic viscosurgical device (OVD) material above and beyond the IOL was removed, and the appropriate IOL position was rechecked and adjusted if necessary. At the San Sebasti an facility, with the patient seated on the surgical table and correct vertical alignment of the patient’s head, patients were asked to look at a distance target (6 m) exactly in front of them to avoid cyclotorsion. Using a sterile marker, the 0-degree and 180-degree axes were marked. Next, with the patient lying on the surgical table, the steep corneal meridian was marked using a Marquez gauge and the preplaced reference points. After IOL implantation, the IOL was rotated into the appropriate position, and the OVD was removed from the anterior chamber and capsular bag using an irrigation/aspiration (I/A) system. The appropriate IOL position was rechecked at the end of surgery. At the Salzburg facility, the IOL was positioned according to intraoperative corneal topography. Eight intraoperative photographs were taken with a Keratron Scout corneal topographer (Optikon 2000 S.p.A.); the axis of the best images were averaged and taken as a reference. After IOL implantation, the IOL was rotated into the appropriate position and the OVD was removed from the anterior chamber and capsular bag using the I/A system. The appropriate IOL position was rechecked at the end of surgery.
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Corneoscleral incisions of 1.8 mm were used at each facility. The incisions were placed at the 12 o’clock position to ensure that no surgically induced corneal astigmatism would influence the preexisting corneal astigmatism.
Postoperative Assessment Postoperatively, patients were examined within the first week and at 3 months. At the first postoperative visit, a slitlamp examination was performed and the UDVA, CDVA, and subjective refraction were evaluated. In addition, PCI measurement was performed to compare preoperative and postoperative keratometric values. Three months postoperatively, the same tests as at the first postoperative visit were performed. In addition, objective refraction, ACD by anterior chamber optical coherence tomography (Visante, Carl Zeiss Meditec AG), and corneal topography were evaluated. In a subgroup of all 20 eyes at the Salzburg center, a slitlamp photograph in retroillumination was taken at the end of surgery and compared with postoperative photographs to document torus position at every visit and to evaluate whether the IOL had rotated.
Vectorial Analysis of Astigmatic Changes Refractive astigmatic changes were evaluated 1 week and 3 months postoperatively by vector analysis using the Alpins method (Assort software, Assort Pty. Ltd.).9,10 The Alpins method allows evaluation that follows 3 fundamental vectors: (1) target induced astigmatism vector (TIA Z change in astigmatic magnitude and axis the surgery was intended to induce), (2) surgically induced astigmatism vector (SIA Z amount and axis of astigmatic change the surgery actually induced), and (3) difference vector (induced astigmatic change by magnitude and axis that would enable initial surgery to achieve its intended target). Furthermore, relationships between these 3 fundamental vectors were calculated at each postoperative visit, defined as follows: (1) correction index, calculated by determining the ratio of SIA to TIA (correction index is preferably 1.0; if the correction index is O1.0 overcorrection occurred, and if the correction index is !1.0, undercorrection occurred), (2) magnitude of error (arithmetic difference between magnitudes of SIA and TIA: magnitude of error O0 indicates overcorrection and magnitude of error !0 undercorrection), (3) angle of error (angle described by the vectors of SIA versus TIA; angle of error O0: achieved correction axis was counterclockwise to where it was intended; angle of error !0: achieved correction was clockwise to its intended axis), (4) index of success (calculated by dividing the difference vector by TIA, representing a relative measure of success [index of success is preferably 0]), (5) coefficient of adjustment (calculated by dividing TIA to SIA, which is the inverse of the correction index and quantifies the modification needed to the initial surgery plan to have achieved a correction index of 1, the ideal correction).
Table 1. Preoperative demographics (88 eyes of 71 patients). Demographic Age (y) Mean G SD Range Sex, n (%) Female Male Operated eyes (n) Right Left Both Axial length (mm) Mean G SD Range Anterior chamber depth (mm) Mean G SD Range Mean implanted IOL power (D) Sphere Mean G SD Range Cylinder Mean G SD Range Predicted postop residual refraction (D) Sphere Mean G SD Range Cylinder Mean G SD Range
Value
64.1 G 19 38, 84 42 (59.2) 29 (40.8) 28 26 17 23.99 G 1.82 20.83, 29.60 3.09 G 0.43 2.05, 4.03
17.37 G 5.38 3.5, 28.0 2.93 G 1.41 9.5, 1.0
0.07 G 0.45 3.12, 0.17 0.20 G 0.11 0.47, 0.00
IOL Z intraocular lens
t test for paired data was applied for all parameter comparisons between preoperative and postoperative data or postoperative data from different controls, if parametric analysis was possible. The Wilcoxon rank-sum test was used to compare preoperative and postoperative values, calculating the level of significance if parametric analysis was not possible. For correlation among different parameters, the Pearson coefficient or Spearman rank order coefficient was applied where appropriate, depending on the normality distribution of the data. To analyze the data from preoperative examinations and postoperative examinations and between consecutive postoperative visits in each IOL group, Kruskal-Wallis 1-way analysis of variance for repeated measures was used.
Statistical Analysis All data were collected in an Excel database, and statistical analysis was computed with SPSS for Windows software (version 15.0, SPSS, Inc.). For every parameter, mean values and standard deviations were calculated. A P value less than 0.05 was the limit for statistical significance. First, for all data samples, normal distribution was checked using the Kolmogorov-Smirnov test. The Student
RESULTS This study enrolled 88 eyes of 71 patients. Table 1 shows the demographic data and implanted toric IOL powers. At 1 trial center, a patient younger (38 years) than the inclusion criteria (O40 years) was included and evaluated during the trial period.
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Table 2. Visual and refractive outcomes over time and corneal topographic and keratometric changes. Parameter Sphere (D) Mean G SD Range Refractive cylinder (D) Mean G SD Range UDVA (logMAR) Mean G SD Range CDVA (logMAR) Mean G SD Range MRSE (D) Mean G SD Range PCI keratometry (mm) R1 Mean G SD Range R2 Mean G SD Range CT keratometry (mm) R1 Mean G SD Range R2 Mean G SD Range
Preop
1 Week Postop
3 Months Postop
P Value*
1.00 G 5.01 16.00, C7.00
0.18 G 0.66 2.75, 1.75
0.18 G 0.68 3.00, 1.75
.259*
2.19 G 1.39 7.00, 0.00
0.50 G 0.53 2.00, 0.00
0.43 G 0.48 2.00, 0.00
!.001†
0.88 G 0.45 0.3, 2.0
0.24 G 0.19 0.08, 0.93
0.15 G 0.18 0.10, 0.70
!.001†
0.31 G 0.15 0.00, 0.70
0.13 G 0.15 0.08, 0.70
0.06 G 0.12 0.10, 0.44
!.001†
2.09 G 4.95 16.50, 5.88
0.07 G 0.60 2.75, 1.38
0.04 G 0.63 3.00, 1.75
!.001z
7.87 G 0.27 7.23, 8.46
7.90 G 0.29 7.39, 8.51
7.85 G 0.27 7.31, 8.57
.63z
7.45 G 0.24 6.61, 7.98
7.47 G 0.24 6.65, 7.90
7.46 G 0.24 6.56, 7.88
.78z
7.72 G 0.36 6.82, 8.63
d d
7.71 G 0.35 6.53, 8.5
.841*
7.56 G 0.27 6.59, 8.12
d d
7.56 G 0.27 6.88, 8.17
.806*
CDVA Z corrected distance visual acuity; CT Z corneal topography; MRSE Z manifest refraction spherical equivalent; PCI Z partial coherence interferometry; R1 Z flat meridian; R2 Z steep meridian; UDVA Z uncorrected distance visual acuity *Preoperative versus 3 months postoperative † Wilcoxon text z Student t test
Visual Acuity and Refraction Table 2 shows refractive and visual acuity outcomes. A statistically significant improvement in UDVA and CDVA occurred after 1 week (both P ! .001) (Figures 1 and 2). In addition, the UDVA and CDVA 3 months postoperatively was statistically significant better than at 1 week (both P ! .001). There was a statistically significant reduction in manifest refraction spherical equivalent and refractive astigmatism from preoperatively to 3 months postoperatively (both P ! .001) (Figures 3 and 4, respectively). At 3 months, the refractive astigmatism was 0.50 D or less in 62 (71%) of the 88 eyes, 1.00 D or less in 81 eyes (92%), 1.50 D or less in 86 eyes (98%), and less than 2.00 D in all eyes (Figure 5). The sphere improved considerably at all postoperative visits compared with preoperative values, although no statistically significant difference was found (1 week,
PZ.25; 3 months, PZ.30), and remained stable over time (1 week to 3 months, PZ.943). There was no significant difference between the predicted residual sphere postoperatively and the achieved postoperative sphere after 1 week (PZ.20) or 3 months (PZ.21). The postoperative high range was caused by a target SE refraction of 3.0 D in several patients. There were no statistically significant differences in the postoperative refractive results (sphere, refractive astigmatism, SE) between unilateral patients and bilateral patients (all PO.05).
Corneal Topographic and Keratometric Changes There were no statistically significant changes in the corneal topographic or keratometric flat meridian or the steep meridian between preoperatively and any postoperative examination (Table 2).
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VECTOR ANALYSIS AFTER TORIC IOL IMPLANTATION
Figure 1. Uncorrected distance visual acuity over time.
Misalignment and Intraocular Lens Rotation In the subgroup analysis of the 20 eyes from the Salzburg facility, the mean rotation of the toric IOL axis was 0.05 degrees G 1.5 (SD) (range 2 to C2 degrees) from the end of surgery to the first postoperative visit and 0.6 G 1.4 degrees (range 3 to C2 degrees) from the end of the surgery to 3 months postoperatively. The differences were not statistically significant. (Clockwise rotation was regarded as positive rotation and counterclockwise as negative rotation.) Vector Analysis Table 3 shows the vector analysis outcomes. The mean magnitude of TIA was 2.37 G 1.15 D (range 0.25 to 7.32), whereas the mean magnitude of SIA was slightly higher at both postoperative visits (Figure 6), indicating a slight overcorrection that was
Figure 3. Stability and spherical equivalent over time. The horizontal line indicates the mean calculated postoperative target SE.
Figure 2. Corrected distance visual acuity over time.
statistically significant at both visits (P ! .01). The magnitude of SIA remained stable over time (PZ.999). There was no statistically significant difference in the magnitude of the difference vector between postoperative visits. Figure 7 shows the difference vector, including the magnitude and its orientation, 3 months postoperatively. The mean correction index (ie, ratio of SIA to TIA; preferably 1) reflected the slight overcorrection (Figure 8) and remained stable over time. The mean magnitude of error was slightly positive (ie, showing overcorrection) during the postoperative follow-up, with no significant difference between visits. The index of success (ie, relative measure of success; preferably 0) was 0.22 G 0.21, and the coefficient of adjustment (ie, inverse of correction index; preferably 1) remained stable over time (PZ.355 and PZ.453, respectively).
Figure 4. Refractive astigmatism over time. The horizontal line indicates the mean calculated postoperative residual refractive astigmatism.
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Table 3. Vector analysis. Parameter
1 Week Postop 3 Months Postop P Value*
The mean angle of error was slightly positive at both postoperative visits (Figure 9). The high postoperative range from 32 to C62 degrees 1 week after implantation was related to 3 necessary secondary procedures to rotate the IOL. The angle of error range afterward improved to 11 to C23 degrees after 3 months.
SIA (D) Mean G SD Range DV (D) Mean G SD Range CI Mean G SD Range ME (D) Mean G SD Range AE ( ) Mean G SD Range IOS Mean G SD Range CA Mean G SD Range
Correlations Between Clinical and Vector Analysis Parameters
AE Z angle of error; CA Z coefficient of adjustment; CI Z correction index; DV Z difference vector; IOS Z index of success; ME Z magnitude of error; SIA Z surgically induced astigmatism *One week postoperative versus 3 months postoperative
Figure 5. Preoperative and postoperative refractive astigmatism.
Table 4 shows correlations between different clinical and vector analysis parameters. Significant positive correlations were found between the difference vector and the UDVA at 1 week and 3 months as well as between the difference vector and the CDVA at 1 week, even though correlation was low. A strong negative correlation was detected between the difference vector and subjective refractive cylinder at each postoperative visit (P ! .001) (Figure 10).
Figure 6. Comparison of TIA and SIA 1 week and 3 months postoperatively (SIA Z surgically induced astigmatism; TIA Z target induced astigmatism).
2.51 G 1.20 0.31, 7.46
2.54 G 1.21 0.63, 7.46
.999
0.52 G 0.44 0.00, 1.80
0.46 G 0.46 0.00, 2.08
.281
1.07 G 0.25 0.37, 1.77
1.09 G 0.21 0.46, 1.77
.425
0.13 G 0.50 1.68, 1.28
0.16 G 0.46 1.67, 1.42
.490
0.25 G 10.01 32, 62
0.63 G 5.68 11, 23
.797
0.27 G 0.26 0.00, 1.24
0.22 G 0.21 0.00, 0.81
.355
1.00 G 0.31 0.57, 2.71
0.96 G 0.24 0.57, 2.16
.453
Complications No severe intraoperative or postoperative complications occurred at the 3 study centers. One eye had implantation of a capsular tension ring because of mild zonulysis of 20 degrees. No eye required a neodymium:YAG capsulotomy up to the last
Figure 7. Difference vector 3 months postoperative. It shows the additional astigmatic change required to attain the intended target of the initial surgery.
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Figure 8. Correction index 3 months postoperatively. The correction index is the ratio of SIA to TIA, and an ideal value would be 1. Values greater than 1 show overcorrection and values less than 1, undercorrection.
postoperative visit. In 3 eyes, a secondary procedure was necessary because of IOL rotational instability or torus misalignment after the first postoperative visit. DISCUSSION In this study, the visual and refractive outcomes and the astigmatic changes assessed using vector analysis were evaluated to determine the efficacy of monofocal bitoric AT Torbi 709M IOL implantation to correct regular corneal astigmatism during cataract surgery. A significant improvement in UDVA and CDVA was achieved, which is consistent with findings in recent studies of the same toric IOL model11 and other toric IOL models.8,12 The improvement between the
Figure 9. Angle of error over time.
1-week and the 3-month examination might be explained by the increased inflammation in the early postoperative period resulting from the trauma of cataract surgery.13 Postoperative cylinder values decreased significantly and remained stable over time, consistent with results in previous studies of the identical IOL model11,14 and in studies of other IOL types.8,12,15,16 The postoperative visual and refractive outcomes confirm the efficacy of the study IOL in correcting corneal astigmatism and cataract in a single surgical procedure. A main factor in the success of a toric IOL is its rotational stability. Rotation of 10 degrees reduces the efficacy of the astigmatic correction by 33%.17
Table 4. Correlations between clinical parameters and vector analysis parameters. 1 Week Postop
3 Months Postop
Parameter
R Value
P Value
R Value
P Value
DV UDVA DV CDVA DV refr cyl ME UDVA ME CDVA ME subj cyl AE preop refr cyl AE preop obj cyl AE refr cyl
0.54 0.25 0.88 0.09 0.06 0.002 0.03 0.10 0.05
!.001 .02 !.001 .40 .62 .99 .80 .39 .64
0.31 0.20 0.92 0.04 0.11 0.07 0.09 0.003 0.02
.004 .07 !.001 .70 .33 .53 .40 .98 .84
AE Z angle of error; CDVA Z corrected distance visual acuity; DV Z difference vector; ME Z magnitude of error; obj cyl Z objective cylinder; refr cyl Z refractive cylinder; UDVA Z uncorrected distance visual acuity
Figure 10. The correlation between the 3-month postoperative difference vector and 3-month postoperative subjective refractive cylinder. Least-square-regression line obtained by the means G standard deviation is shown. The linear model indicates a strong negative correlation (r2 Z 0.92).
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Intraocular lens rotation is caused by several factors, including IOL adhesion to the capsular bag. It has been reported that acrylic IOLs form the strongest adhesions to the capsular bag, followed by poly(methyl methacrylate) and silicone IOLs.18 The current study IOL is hydrophilic acrylate with a hydrophobic surface; thus, this IOL’s biomaterial should guarantee the strongest adhesion. Other reported factors in IOL rotation are incomplete OVD removal,19 early postoperative IOL fluctuations,20 and capsulorhexis size.17 Intraocular lens rotation can be measured by different techniques. Because the analysis of intraoperative and postoperative photographs in retroillumination has been described as an effective method to determine possible IOL rotation,21 this method was used in the current study in a subgroup analysis. Bascaran et al.11 found a mean IOL rotation of 4.42 G 4.31 degrees (range 0 to 16 degrees) and Scialdone et al.22 found a mean IOL rotation of 3.0 G 3.1 degrees (range 0 to 11 degrees) with the identical IOL model used in our study. Similar IOL rotation results were reported other available toric IOLs, with the amount ranging from 0.23 G 1.9 degrees23 up to 9.42 G 7.80 degrees.8,15,16,23–25 We measured a mean IOL rotation of 0.6 G 1.4 degrees (range 3 to C2 degrees) in a single-center subgroup analysis of 20 patients. Of all 88 implanted IOLs, 3 IOLs had to be rotated within the first week after implantation, raising the suspicion that incomplete OVD removal might have been the reason for these early rotations. Because rotation of a toric IOL causes residual astigmatism, vector analysis was applied to evaluate the changes in refractive astigmatism in terms of the magnitude and orientation of this variable. To our knowledge, this is the first report of vector analysis of the AT Torbi 709M IOL. Calculation of 3 fundamental vectorsdthe TIA, SIA, and difference vectordconstitutes the basis of the Alpins vector analysis method.9,10 In an ideal correction, the TIA and SIA would be identical and the resulting difference vector would be 0. In the current study, the TIA was lower than the SIA, indicating slight overcorrection; however, no significant changes in SIA occurred during the follow-up, indicating that the SIA remained stable over time, which is consistent with findings in other toric IOL studies.12,26 Although Figure 7 shows that a mean difference vector of 0.3 at 83 degrees is present, Figure 8 visually describes that the range of the achieved correction (ie, correction index) varies between 0.46 and 1.77; 1.0 would correspond to the ideal postoperative result. Therefore, no overall recommendation
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regarding a possible surgeon adjustment can be given. The calculated correlations between the 3 fundamental vectors describe the overall success of the treatment, the potential overcorrection or undercorrection, and the misalignment of treatment.9,10 The correction index of 1.09 and the mean positive magnitude of error of 0.16 G 0.46 reflect slight overcorrection of the achieved astigmatic treatment. A possible explanation for the overcorrection could be underestimation of the toric IOL power at the corneal plane by the manufacturer, as previously described,27 or slight measurement errors using PCI-measured keratometry values that might have caused the slight overcorrection. Previous studies of vector analysis after implantation of other toric IOL models showed overcorrection23,28 as well as undercorrection.12,26 The angle of error indicates the misalignment of treatment. A positive angle of error value indicates a slight mean counterclockwise rotation to the intended axis and is consistent with reported rotation in previous studies.8,11,15,16,22–25 The mean angle of error remained stable over time, which agrees with findings in other toric IOL studies.12,28 The mean absolute angle of error was slightly higher than the rotation measured by comparison of the retroillumination photographs in the single-center subgroup analysis; however, this is less informative because of the limited number of patients in that subgroup. Further examinations comparing the angle of error and measured IOL rotation should be performed to provide a better understanding of the correlation and clinical interpretation. In addition, clinical parameters were correlated with vector analysis parameters. A strong negative correlation between the magnitude of difference vector and refractive cylinder in all postoperative visits could be seen, showing that a larger difference vector is associated with higher residual refractive cylinders. These findings were consistent with those of Ali o et al.12 using a different toric IOL model. Furthermore, the UDVA was correlated with the magnitude of difference vector, indicating that a larger difference vector negatively influences the UDVA. That eyes with a larger difference vector also had worse CDVA at the 1-week visit might be explained by higher amounts of higher-order aberrations in those cases, as hypothesized in literature. 12 However, this topic requires further study. In conclusion, implantation of the AT Torbi 709M IOL during cataract surgery seems to be a safe, effective, predictable, and stable procedure to correct regular corneal astigmatism.
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WHAT WAS KNOWN Implantation of the monofocal bitoric aspheric IOL used in this study is an effective procedure to correct preexisting corneal astigmatism within cataract surgery. WHAT THIS PAPER ADDS Refractive cylinder was reduced significantly, concurrent with visual improvement, by implantation of this toric IOL during routine cataract surgery. Vector analysis showed a small trend toward overcorrection that remained stable over time.
REFERENCES €tz WW. Analysis of biometry and prevalence 1. Hoffmann PC, Hu data for corneal astigmatism in 23,239 eyes. J Cataract Refract Surg 2010; 36:1479–1485 2. Titiyal JS, Agarwal T, Jhanji V. Toric intraocular lens versus opposite clear corneal incisions to correct astigmatism in eyes having cataract surgery. J Cataract Refract Surg 2009; 35:1834–1835 3. Ganekal S, Dorairaj S, Jhanji V. Limbal relaxing incisions during phacoemulsification: 6-month results. J Cataract Refract Surg 2011; 37:2081–2082 €ckl T, Dexl AK, Bachernegg A, Reischl V, Riha W, 4. Ru Ruckhofer J, Binder PS, Grabner G. Femtosecond laser–assisted intrastromal arcuate keratotomy to reduce corneal astigmatism. J Cataract Refract Surg 2013; 39:528–538 5. Norouzi H, Rahmati-Kamel M. Laser in situ keratomileusis for correction of induced astigmatism from cataract surgery. J Refract Surg 2003; 19:416–424 6. Gunvant P, Ablamowicz A, Gollamudi S. Predicting the necessity of LASIK enhancement after cataract surgery in patients with multifocal IOL implantation. Clin Ophthalmol 2011; 5:1281–1285. Available at: http://www.ncbi.nlm.nih. gov/pmc/articles/PMC3180499/pdf/opth-5-1281.pdf. Accessed December 11, 2014 7. Auffarth GU, Rabsilber TM. Torische Hinterkammerlinsen nach Kataraktoperation und refraktivem Linsenaustausch [Toric IOLs after cataract surgery and refractive lens exchange]. Ophthalmologe 2007; 104:1024–1031 €ckl T, Riha W, Grabner G, Dexl AK. Rota8. Bachernegg A, Ru tional stability and visual outcome after implantation of a new toric intraocular lens for the correction of corneal astigmatism during cataract surgery. J Cataract Refract Surg 2013; 39:1390–1398 9. Alpins NA. A new method of analyzing vectors for changes in astigmatism. J Cataract Refract Surg 1993; 19:524–533 10. Alpins N. Astigmatism analysis by the Alpins method. J Cataract Refract Surg 2001; 27:31–49 11. Bascaran L, Mendicute J, Macias-Murelaga B, Arbelaitz N, Martinez-Soroa I. Efficacy and stability of AT TORBI 709 M toric IOL. J Refract Surg 2013; 29:194–199 JL, Pin ~ero DP, Toma s J, Aleso n A. Vector analysis of 12. Alio astigmatic changes after cataract surgery with toric intraocular lens implantation. J Cataract Refract Surg 2011; 37:1038–1049
13. Findl O, Amon M, Petternel V, Kruger A. Early objective assessment of intraocular inflammation after phacoemulsification cataract surgery. J Cataract Refract Surg 2003; 29:2143– 2147 14. Ale JB, Power J, Zohs K, Cunningham F. Refractive and visual outcome of toric intraocular lens implantation following cataract surgery. Nepal J Ophthalmol 2012; 4:37–44. Available at: http:// www.nepjol.info/index.php/NEPJOPH/article/download/5848/48 08. Accessed December 11, 2014 15. Holland E, Lane S, Horn JD, Ernest P, Arleo R, Miller KM. The AcrySof toric intraocular lens in subjects with cataracts and corneal astigmatism; a randomized, subject-masked, parallel-group, 1-year study. Ophthalmology 2010; 117:2104–2111 16. Sheppard AL, Wolffsohn JS, Bhatt U, Hoffmann PC, Scheider A, €tz WW, Shah S. Clinical outcomes after implantation of a new Hu hydrophobic acrylic toric IOL during routine cataract surgery. J Cataract Refract Surg 2013; 39:41–47 17. Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: correcting astigmatism while controlling axis shift. J Cataract Refract Surg 1994; 20:523–526 18. Oshika T, Nagata T, Ishii Y. Adhesion of lens capsule to intraocular lenses of polymethylmethacrylate, silicone, and acrylic foldable materials: an experimental study. Br J Ophthalmol 1998; 82:549–553. Available at: http://www.pubmedcentral. nih.gov/picrender.fcgi?artidZ1722579&blobtypeZpdf. Accessed December 11, 2014 19. Myers TD, Olson RJ. Comparison of the effects of viscoelastic agents on clinical properties of the Unfolder lens injection system. J Cataract Refract Surg 1999; 25:953– 958 20. Pereira FAS, Milverton EJ, Coroneo MT. Miyake-Apple study of the rotational stability of the Acrysof toric intraocular lens after experimental eye trauma. Eye 2010; 24:376–378. Available at: http:// www.nature.com/eye/journal/v24/n2/pdf/eye2009150a.pdf. Accessed December 11, 2014 €lcker HE. Messmethode zur Bestim21. Becker KA, Auffarth GU, Vo mung der Rotation und der Dezentrierung von Intraokularlinsen [Measurement method for the determination of rotation and decentration of intraocular lenses]. Ophthalmologe 2001; 101:600–603 22. Scialdone A, De Gaetano F, Monaco G. Visual performance of 2 aspheric toric intraocular lenses: comparative study. J Cataract Refract Surg 2013; 39:906–914 €tz WW. Results of higher power toric 23. Hoffmann PC, Auel S, Hu intraocular lens implantation. J Cataract Refract Surg 2011; 37:1411–1418 24. Chua W-H, 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; 38:620–624 25. Visser N, Berendschot TTJM, Bauer NJC, Jurich J, Kersting O, Nuijts RMMA. Accuracy of toric intraocular lens implantation in cataract and refractive surgery. J Cataract Refract Surg 2011; 37:1394–1402 26. Visser N, Berendschot TTJM, Bauer NJC, Nuijts RMMA. Vector analysis of corneal and refractive astigmatism changes following toric pseudophakic and toric phakic IOL implantation. Invest Ophthalmol Vis Sci 2012; 53:1865–1873. Available at: http:// www.iovs.org/content/53/4/1865.full.pdf. Accessed December 11, 2014 27. Goggin M, Moore S, Esterman A. Toric intraocular lens outcome using the manufacturer’s prediction of corneal plane equivalent intraocular lens cylinder power. Arch Ophthalmol 2011;
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129:1004–1008. Available at: http://archopht.jamanetwork. com/data/Journals/OPHTH/22540/ecs05116_1004_1008.pdf. Accessed December 11, 2014 JL, Pin ~ero DP, Toma s J, Plaza AB. Vector analysis of astig28. Alio matic changes after cataract surgery with implantation of a new toric multifocal intraocular lens. J Cataract Refract Surg 2011; 37:1217–1229
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EE/$FILE/AT_TORBI709Datasheet_GB_FINAL.pdf. Accessed December 11, 2014
OTHER CITED MATERIAL A. Carl Zeiss Meditec AG. TORBI 709, AT TORBI 709MP preloaded. Specifications. Available at: http://applications.zeiss.com/ C1257A290053AE30/0/538ECA28392347FDC1257A29005812
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First author: Eva M. Krall, MD Department of Ophthalmology, Paracelsus Medical University, Salzburg, Austria
Vector analysis of astigmatism correction after toric intraocular lens implantation Eva M. Krall, MD, Eva M. Arlt, MD, Melchior Hohensinn, MD, Sarah Moussa, MD, Gerlinde Jell, MD, Jorge L. Ali o, MD, PhD, Ana B. Plaza-Puche, MD, MSc, Lucia Bascaran, MD, Javier Mendicute, MD, PhD, G€ unther Grabner, MD, Alois K. Dexl, MD, MSc
PURPOSE: To determine astigmatic changes by vector analysis and postoperative refractive and visual outcomes after implantation of the monofocal aspheric bitoric AT Torbi 709M toric intraocular lens (IOL). SETTING: Three centers in Salzburg, Austria, and Alicante and San Sebastian, Spain. DESIGN: Prospective interventional case series. METHODS: Preoperative and postoperative visual acuity, subjective and objective refractions, and corneal radii using a topographer were examined in all patients. All patients had postoperative examinations within the first week and at 6 to 12 weeks. Astigmatic changes were evaluated using the Alpins vector method based on 3 fundamental vectors as follows: target induced astigmatism (TIA), surgically induced astigmatism (SIA), and difference vector. The various relationships between these 3 vectors were calculated, providing an extensive description of the astigmatic correction achieved. RESULTS: Eighty-eight eyes (71 patients) were included. Postoperatively, refractive cylinder was reduced significantly (P < .001), concurrent with visual improvement. The mean magnitude of the SIA vector (2.54 diopters [D] G 1.21 [SD]) was slightly higher than the mean magnitude of the TIA vector (2.37 G 1.15 D) at the last follow-up. The mean difference vector was 0.46 G 0.46 D, the mean magnitude of error was 0.16 G 0.46 D, and the mean correction index was 1.09 G 0.21, all indicating minimal overcorrection at 3 months that remained stable during the follow-up. CONCLUSION: Implantation of the toric IOL was safe and effective for the treatment of eyes with cataract in combination with preexisting regular corneal astigmatism over a short-term follow-up. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:790–799 Q 2015 ASCRS and ESCRS
Modern cataract surgery offers the possibility of compensating for spherical and astigmatic refractive errors, thus providing enhanced visual rehabilitation. In a recent biometry study of 23 239 eyes,1 corneal astigmatism of 1.0 diopter (D) or more was observed in 28% of patients. Several techniques, including opposite clear corneal incisions,2 limbal relaxing incisions,3 femtosecond laser–assisted astigmatic keratotomy,4 excimer laser refractive procedures,5,6 and toric intraocular lens (IOL) implantation,7 are available to correct regular corneal astigmatism. The implantation of toric IOLs is an effective treatment of lens opacification and concomitant regular corneal astigmatism in a single surgical procedure and has been proven to be safe and predictable.8 790
Q 2015 ASCRS and ESCRS Published by Elsevier Inc.
To evaluate the efficacy of toric IOL implantation, astigmatic change can be determined by vector analysis considering its magnitude and axis. In brief, vector analysis determines a goal for astigmatism correction and a treatment required to achieve that goal. The method also allows the calculation of the principal components by which an operation fails to achieve its goal and other components that assist in comparing the results of astigmatism surgery in individuals and groups of individuals.9,10 The purpose of this study was to determine the astigmatic changes using vector analysis as well as postoperative refractive and visual outcomes within the first 3 months after implantation of the AT Torbi 709M toric IOL (Carl Zeiss Meditec AG). http://dx.doi.org/10.1016/j.jcrs.2014.07.038 0886-3350
VECTOR ANALYSIS AFTER TORIC IOL IMPLANTATION
PATIENTS AND METHODS Patient Population This clinical trial was designed as a prospective multicenter interventional case series with 3 participating ophthalmologic centers as follows: Vissum Corporation, Division of Ophthalmology, Universidad Miguel Hern andez, Alicante, Spain; Ophthalmology Service, Donostia Hospital, San Sebastian, Spain; and Department of Ophthalmology, Paracelsus Medical University, Salzburg, Austria. The study was performed in accordance with the tenets of the Declaration of Helsinki and approved by each center’s local institutional review board or ethics committee. After receiving a detailed explanation of the purpose, procedure, and patient responsibilities, all trial patients provided signed informed consent for participation in this study. Patients were eligible for inclusion if they were older than 40 years, had age-related cataract with regular corneal astigmatism without additional ocular pathology, had a stable corneal condition, and had refraction within the past 12 months. Exclusion criteria were irregular corneal astigmatism, serious intraoperative complications, glaucoma, pseudoexfoliation syndrome, uveitis, macular degeneration or other retinal impairment, corneal scarring, amblyopia with a corrected distance visual acuity less than 0.5, and a need for a toric IOL outside the available spherical range (10.0 to C32.0 D) and/or outside cylindrical range (1.0 to 12.0 D).
Preoperative Assessment Before surgery, a complete medical history was taken and all patients had a full ophthalmologic examination including refraction and uncorrected (UDVA) and corrected (CDVA) distance visual acuity measurements. The Early Treatment Diabetic Retinopathy Study charts at a test distance of 4 m were used by counting the numbers of optotypes the patient identified correctly and converting this number into logMAR
Submitted: April 3, 2014. Final revision submitted: July 5, 2014. Accepted: July 15, 2014. From the Department of Ophthalmology (Krall, Arlt, Hohensinn, Moussa, Jell, Grabner, Dexl), Paracelsus Medical University, Salzburg, Austria; the Division of Ophthalmology (Alio, Plaza-Puche), Vissum Corporation, Universidad Miguel Hernandez, Alicante, and the Ophthalmology Service (Bascaran, Mendicute), Donostia Hospital, San Sebastian, Spain. Supported by the Fuchs Foundation for the Promotion of Research in Ophthalmology, Salzburg, Austria. Carl Zeiss Meditec AG, Jena, Germany, financially supports the Fuchs Foundation as the clinical research center of the Department of Ophthalmology of the Paracelsus Medical University, Salzburg, Austria (grant 23-2011). Presented at the XXX Congress of the European Society of Cataract and Refractive Surgeons, Amsterdam, the Netherlands, October 2013. Corresponding author: Alois K. Dexl, MD, MSc, Department of Ophthalmology, Paracelsus Medical University, M€ ullner Hauptstraße 48, A-5020 Salzburg, Austria. E-mail: [email protected].
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values. Keratometric values were measured with partial coherence interferometry (PCI) (IOLMaster, Carl Zeiss Meditec AG) for IOL calculation, and corneal topography was performed to ensure regularity of the corneal astigmatism. Intraocular lens power calculation was performed using the online calculation program Z CALC (Carl Zeiss Meditec AG). This calculation program requires the input of the following PCI data: axial length, anterior chamber depth (ACD), keratometry values in diopters, and IOL type to be implanted.
Intraocular Lens The AT Torbi 709M is a monofocal bitoric aspheric IOL with an optic diameter of 6.0 mm and a total diameter of 11.0 mm. The optic design provides aberration-neutral convergent incidence of light.A The optic material of the IOL is foldable hydrophilic acrylate with a hydrophobic surface and 25% water content and an ultraviolet filter. The haptic angulation is 0 degrees, and the IOL is available in spherical ranges of 10.0 to C32.0 D in 0.5 D increments and in toric ranges of C1.0 to C12.0 D in 0.5 D increments.A
Surgical Technique One experienced surgeon (G.G., J.L.A., J.M.) performed all surgeries at each center using topical anesthesia. All patients were operated on with a standard sutureless phacoemulsification technique. In all cases, the IOL was implanted in the capsular bag with the single-use injector A6/AT. Smart Cartridge Set (Carl Zeiss Meditec AG), requiring an incision width of at least 1.8 mm. Surgical preparation, IOL implantation, postoperative treatment, and postoperative medication were performed/applied corresponding to the routine procedure of the respective center. At the Alicante facility, both the 0-degree axis and 180-degree axis were marked with a needle on the corneal epithelium with the patient seated at the slitlamp. The IOL was implanted in the axis corresponding to the calculation program, with the 180-degree premarked axis acting as a reference. After IOL implantation, all ophthalmic viscosurgical device (OVD) material above and beyond the IOL was removed, and the appropriate IOL position was rechecked and adjusted if necessary. At the San Sebasti an facility, with the patient seated on the surgical table and correct vertical alignment of the patient’s head, patients were asked to look at a distance target (6 m) exactly in front of them to avoid cyclotorsion. Using a sterile marker, the 0-degree and 180-degree axes were marked. Next, with the patient lying on the surgical table, the steep corneal meridian was marked using a Marquez gauge and the preplaced reference points. After IOL implantation, the IOL was rotated into the appropriate position, and the OVD was removed from the anterior chamber and capsular bag using an irrigation/aspiration (I/A) system. The appropriate IOL position was rechecked at the end of surgery. At the Salzburg facility, the IOL was positioned according to intraoperative corneal topography. Eight intraoperative photographs were taken with a Keratron Scout corneal topographer (Optikon 2000 S.p.A.); the axis of the best images were averaged and taken as a reference. After IOL implantation, the IOL was rotated into the appropriate position and the OVD was removed from the anterior chamber and capsular bag using the I/A system. The appropriate IOL position was rechecked at the end of surgery.
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Corneoscleral incisions of 1.8 mm were used at each facility. The incisions were placed at the 12 o’clock position to ensure that no surgically induced corneal astigmatism would influence the preexisting corneal astigmatism.
Postoperative Assessment Postoperatively, patients were examined within the first week and at 3 months. At the first postoperative visit, a slitlamp examination was performed and the UDVA, CDVA, and subjective refraction were evaluated. In addition, PCI measurement was performed to compare preoperative and postoperative keratometric values. Three months postoperatively, the same tests as at the first postoperative visit were performed. In addition, objective refraction, ACD by anterior chamber optical coherence tomography (Visante, Carl Zeiss Meditec AG), and corneal topography were evaluated. In a subgroup of all 20 eyes at the Salzburg center, a slitlamp photograph in retroillumination was taken at the end of surgery and compared with postoperative photographs to document torus position at every visit and to evaluate whether the IOL had rotated.
Vectorial Analysis of Astigmatic Changes Refractive astigmatic changes were evaluated 1 week and 3 months postoperatively by vector analysis using the Alpins method (Assort software, Assort Pty. Ltd.).9,10 The Alpins method allows evaluation that follows 3 fundamental vectors: (1) target induced astigmatism vector (TIA Z change in astigmatic magnitude and axis the surgery was intended to induce), (2) surgically induced astigmatism vector (SIA Z amount and axis of astigmatic change the surgery actually induced), and (3) difference vector (induced astigmatic change by magnitude and axis that would enable initial surgery to achieve its intended target). Furthermore, relationships between these 3 fundamental vectors were calculated at each postoperative visit, defined as follows: (1) correction index, calculated by determining the ratio of SIA to TIA (correction index is preferably 1.0; if the correction index is O1.0 overcorrection occurred, and if the correction index is !1.0, undercorrection occurred), (2) magnitude of error (arithmetic difference between magnitudes of SIA and TIA: magnitude of error O0 indicates overcorrection and magnitude of error !0 undercorrection), (3) angle of error (angle described by the vectors of SIA versus TIA; angle of error O0: achieved correction axis was counterclockwise to where it was intended; angle of error !0: achieved correction was clockwise to its intended axis), (4) index of success (calculated by dividing the difference vector by TIA, representing a relative measure of success [index of success is preferably 0]), (5) coefficient of adjustment (calculated by dividing TIA to SIA, which is the inverse of the correction index and quantifies the modification needed to the initial surgery plan to have achieved a correction index of 1, the ideal correction).
Table 1. Preoperative demographics (88 eyes of 71 patients). Demographic Age (y) Mean G SD Range Sex, n (%) Female Male Operated eyes (n) Right Left Both Axial length (mm) Mean G SD Range Anterior chamber depth (mm) Mean G SD Range Mean implanted IOL power (D) Sphere Mean G SD Range Cylinder Mean G SD Range Predicted postop residual refraction (D) Sphere Mean G SD Range Cylinder Mean G SD Range
Value
64.1 G 19 38, 84 42 (59.2) 29 (40.8) 28 26 17 23.99 G 1.82 20.83, 29.60 3.09 G 0.43 2.05, 4.03
17.37 G 5.38 3.5, 28.0 2.93 G 1.41 9.5, 1.0
0.07 G 0.45 3.12, 0.17 0.20 G 0.11 0.47, 0.00
IOL Z intraocular lens
t test for paired data was applied for all parameter comparisons between preoperative and postoperative data or postoperative data from different controls, if parametric analysis was possible. The Wilcoxon rank-sum test was used to compare preoperative and postoperative values, calculating the level of significance if parametric analysis was not possible. For correlation among different parameters, the Pearson coefficient or Spearman rank order coefficient was applied where appropriate, depending on the normality distribution of the data. To analyze the data from preoperative examinations and postoperative examinations and between consecutive postoperative visits in each IOL group, Kruskal-Wallis 1-way analysis of variance for repeated measures was used.
Statistical Analysis All data were collected in an Excel database, and statistical analysis was computed with SPSS for Windows software (version 15.0, SPSS, Inc.). For every parameter, mean values and standard deviations were calculated. A P value less than 0.05 was the limit for statistical significance. First, for all data samples, normal distribution was checked using the Kolmogorov-Smirnov test. The Student
RESULTS This study enrolled 88 eyes of 71 patients. Table 1 shows the demographic data and implanted toric IOL powers. At 1 trial center, a patient younger (38 years) than the inclusion criteria (O40 years) was included and evaluated during the trial period.
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Table 2. Visual and refractive outcomes over time and corneal topographic and keratometric changes. Parameter Sphere (D) Mean G SD Range Refractive cylinder (D) Mean G SD Range UDVA (logMAR) Mean G SD Range CDVA (logMAR) Mean G SD Range MRSE (D) Mean G SD Range PCI keratometry (mm) R1 Mean G SD Range R2 Mean G SD Range CT keratometry (mm) R1 Mean G SD Range R2 Mean G SD Range
Preop
1 Week Postop
3 Months Postop
P Value*
1.00 G 5.01 16.00, C7.00
0.18 G 0.66 2.75, 1.75
0.18 G 0.68 3.00, 1.75
.259*
2.19 G 1.39 7.00, 0.00
0.50 G 0.53 2.00, 0.00
0.43 G 0.48 2.00, 0.00
!.001†
0.88 G 0.45 0.3, 2.0
0.24 G 0.19 0.08, 0.93
0.15 G 0.18 0.10, 0.70
!.001†
0.31 G 0.15 0.00, 0.70
0.13 G 0.15 0.08, 0.70
0.06 G 0.12 0.10, 0.44
!.001†
2.09 G 4.95 16.50, 5.88
0.07 G 0.60 2.75, 1.38
0.04 G 0.63 3.00, 1.75
!.001z
7.87 G 0.27 7.23, 8.46
7.90 G 0.29 7.39, 8.51
7.85 G 0.27 7.31, 8.57
.63z
7.45 G 0.24 6.61, 7.98
7.47 G 0.24 6.65, 7.90
7.46 G 0.24 6.56, 7.88
.78z
7.72 G 0.36 6.82, 8.63
d d
7.71 G 0.35 6.53, 8.5
.841*
7.56 G 0.27 6.59, 8.12
d d
7.56 G 0.27 6.88, 8.17
.806*
CDVA Z corrected distance visual acuity; CT Z corneal topography; MRSE Z manifest refraction spherical equivalent; PCI Z partial coherence interferometry; R1 Z flat meridian; R2 Z steep meridian; UDVA Z uncorrected distance visual acuity *Preoperative versus 3 months postoperative † Wilcoxon text z Student t test
Visual Acuity and Refraction Table 2 shows refractive and visual acuity outcomes. A statistically significant improvement in UDVA and CDVA occurred after 1 week (both P ! .001) (Figures 1 and 2). In addition, the UDVA and CDVA 3 months postoperatively was statistically significant better than at 1 week (both P ! .001). There was a statistically significant reduction in manifest refraction spherical equivalent and refractive astigmatism from preoperatively to 3 months postoperatively (both P ! .001) (Figures 3 and 4, respectively). At 3 months, the refractive astigmatism was 0.50 D or less in 62 (71%) of the 88 eyes, 1.00 D or less in 81 eyes (92%), 1.50 D or less in 86 eyes (98%), and less than 2.00 D in all eyes (Figure 5). The sphere improved considerably at all postoperative visits compared with preoperative values, although no statistically significant difference was found (1 week,
PZ.25; 3 months, PZ.30), and remained stable over time (1 week to 3 months, PZ.943). There was no significant difference between the predicted residual sphere postoperatively and the achieved postoperative sphere after 1 week (PZ.20) or 3 months (PZ.21). The postoperative high range was caused by a target SE refraction of 3.0 D in several patients. There were no statistically significant differences in the postoperative refractive results (sphere, refractive astigmatism, SE) between unilateral patients and bilateral patients (all PO.05).
Corneal Topographic and Keratometric Changes There were no statistically significant changes in the corneal topographic or keratometric flat meridian or the steep meridian between preoperatively and any postoperative examination (Table 2).
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Figure 1. Uncorrected distance visual acuity over time.
Misalignment and Intraocular Lens Rotation In the subgroup analysis of the 20 eyes from the Salzburg facility, the mean rotation of the toric IOL axis was 0.05 degrees G 1.5 (SD) (range 2 to C2 degrees) from the end of surgery to the first postoperative visit and 0.6 G 1.4 degrees (range 3 to C2 degrees) from the end of the surgery to 3 months postoperatively. The differences were not statistically significant. (Clockwise rotation was regarded as positive rotation and counterclockwise as negative rotation.) Vector Analysis Table 3 shows the vector analysis outcomes. The mean magnitude of TIA was 2.37 G 1.15 D (range 0.25 to 7.32), whereas the mean magnitude of SIA was slightly higher at both postoperative visits (Figure 6), indicating a slight overcorrection that was
Figure 3. Stability and spherical equivalent over time. The horizontal line indicates the mean calculated postoperative target SE.
Figure 2. Corrected distance visual acuity over time.
statistically significant at both visits (P ! .01). The magnitude of SIA remained stable over time (PZ.999). There was no statistically significant difference in the magnitude of the difference vector between postoperative visits. Figure 7 shows the difference vector, including the magnitude and its orientation, 3 months postoperatively. The mean correction index (ie, ratio of SIA to TIA; preferably 1) reflected the slight overcorrection (Figure 8) and remained stable over time. The mean magnitude of error was slightly positive (ie, showing overcorrection) during the postoperative follow-up, with no significant difference between visits. The index of success (ie, relative measure of success; preferably 0) was 0.22 G 0.21, and the coefficient of adjustment (ie, inverse of correction index; preferably 1) remained stable over time (PZ.355 and PZ.453, respectively).
Figure 4. Refractive astigmatism over time. The horizontal line indicates the mean calculated postoperative residual refractive astigmatism.
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Table 3. Vector analysis. Parameter
1 Week Postop 3 Months Postop P Value*
The mean angle of error was slightly positive at both postoperative visits (Figure 9). The high postoperative range from 32 to C62 degrees 1 week after implantation was related to 3 necessary secondary procedures to rotate the IOL. The angle of error range afterward improved to 11 to C23 degrees after 3 months.
SIA (D) Mean G SD Range DV (D) Mean G SD Range CI Mean G SD Range ME (D) Mean G SD Range AE ( ) Mean G SD Range IOS Mean G SD Range CA Mean G SD Range
Correlations Between Clinical and Vector Analysis Parameters
AE Z angle of error; CA Z coefficient of adjustment; CI Z correction index; DV Z difference vector; IOS Z index of success; ME Z magnitude of error; SIA Z surgically induced astigmatism *One week postoperative versus 3 months postoperative
Figure 5. Preoperative and postoperative refractive astigmatism.
Table 4 shows correlations between different clinical and vector analysis parameters. Significant positive correlations were found between the difference vector and the UDVA at 1 week and 3 months as well as between the difference vector and the CDVA at 1 week, even though correlation was low. A strong negative correlation was detected between the difference vector and subjective refractive cylinder at each postoperative visit (P ! .001) (Figure 10).
Figure 6. Comparison of TIA and SIA 1 week and 3 months postoperatively (SIA Z surgically induced astigmatism; TIA Z target induced astigmatism).
2.51 G 1.20 0.31, 7.46
2.54 G 1.21 0.63, 7.46
.999
0.52 G 0.44 0.00, 1.80
0.46 G 0.46 0.00, 2.08
.281
1.07 G 0.25 0.37, 1.77
1.09 G 0.21 0.46, 1.77
.425
0.13 G 0.50 1.68, 1.28
0.16 G 0.46 1.67, 1.42
.490
0.25 G 10.01 32, 62
0.63 G 5.68 11, 23
.797
0.27 G 0.26 0.00, 1.24
0.22 G 0.21 0.00, 0.81
.355
1.00 G 0.31 0.57, 2.71
0.96 G 0.24 0.57, 2.16
.453
Complications No severe intraoperative or postoperative complications occurred at the 3 study centers. One eye had implantation of a capsular tension ring because of mild zonulysis of 20 degrees. No eye required a neodymium:YAG capsulotomy up to the last
Figure 7. Difference vector 3 months postoperative. It shows the additional astigmatic change required to attain the intended target of the initial surgery.
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Figure 8. Correction index 3 months postoperatively. The correction index is the ratio of SIA to TIA, and an ideal value would be 1. Values greater than 1 show overcorrection and values less than 1, undercorrection.
postoperative visit. In 3 eyes, a secondary procedure was necessary because of IOL rotational instability or torus misalignment after the first postoperative visit. DISCUSSION In this study, the visual and refractive outcomes and the astigmatic changes assessed using vector analysis were evaluated to determine the efficacy of monofocal bitoric AT Torbi 709M IOL implantation to correct regular corneal astigmatism during cataract surgery. A significant improvement in UDVA and CDVA was achieved, which is consistent with findings in recent studies of the same toric IOL model11 and other toric IOL models.8,12 The improvement between the
Figure 9. Angle of error over time.
1-week and the 3-month examination might be explained by the increased inflammation in the early postoperative period resulting from the trauma of cataract surgery.13 Postoperative cylinder values decreased significantly and remained stable over time, consistent with results in previous studies of the identical IOL model11,14 and in studies of other IOL types.8,12,15,16 The postoperative visual and refractive outcomes confirm the efficacy of the study IOL in correcting corneal astigmatism and cataract in a single surgical procedure. A main factor in the success of a toric IOL is its rotational stability. Rotation of 10 degrees reduces the efficacy of the astigmatic correction by 33%.17
Table 4. Correlations between clinical parameters and vector analysis parameters. 1 Week Postop
3 Months Postop
Parameter
R Value
P Value
R Value
P Value
DV UDVA DV CDVA DV refr cyl ME UDVA ME CDVA ME subj cyl AE preop refr cyl AE preop obj cyl AE refr cyl
0.54 0.25 0.88 0.09 0.06 0.002 0.03 0.10 0.05
!.001 .02 !.001 .40 .62 .99 .80 .39 .64
0.31 0.20 0.92 0.04 0.11 0.07 0.09 0.003 0.02
.004 .07 !.001 .70 .33 .53 .40 .98 .84
AE Z angle of error; CDVA Z corrected distance visual acuity; DV Z difference vector; ME Z magnitude of error; obj cyl Z objective cylinder; refr cyl Z refractive cylinder; UDVA Z uncorrected distance visual acuity
Figure 10. The correlation between the 3-month postoperative difference vector and 3-month postoperative subjective refractive cylinder. Least-square-regression line obtained by the means G standard deviation is shown. The linear model indicates a strong negative correlation (r2 Z 0.92).
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Intraocular lens rotation is caused by several factors, including IOL adhesion to the capsular bag. It has been reported that acrylic IOLs form the strongest adhesions to the capsular bag, followed by poly(methyl methacrylate) and silicone IOLs.18 The current study IOL is hydrophilic acrylate with a hydrophobic surface; thus, this IOL’s biomaterial should guarantee the strongest adhesion. Other reported factors in IOL rotation are incomplete OVD removal,19 early postoperative IOL fluctuations,20 and capsulorhexis size.17 Intraocular lens rotation can be measured by different techniques. Because the analysis of intraoperative and postoperative photographs in retroillumination has been described as an effective method to determine possible IOL rotation,21 this method was used in the current study in a subgroup analysis. Bascaran et al.11 found a mean IOL rotation of 4.42 G 4.31 degrees (range 0 to 16 degrees) and Scialdone et al.22 found a mean IOL rotation of 3.0 G 3.1 degrees (range 0 to 11 degrees) with the identical IOL model used in our study. Similar IOL rotation results were reported other available toric IOLs, with the amount ranging from 0.23 G 1.9 degrees23 up to 9.42 G 7.80 degrees.8,15,16,23–25 We measured a mean IOL rotation of 0.6 G 1.4 degrees (range 3 to C2 degrees) in a single-center subgroup analysis of 20 patients. Of all 88 implanted IOLs, 3 IOLs had to be rotated within the first week after implantation, raising the suspicion that incomplete OVD removal might have been the reason for these early rotations. Because rotation of a toric IOL causes residual astigmatism, vector analysis was applied to evaluate the changes in refractive astigmatism in terms of the magnitude and orientation of this variable. To our knowledge, this is the first report of vector analysis of the AT Torbi 709M IOL. Calculation of 3 fundamental vectorsdthe TIA, SIA, and difference vectordconstitutes the basis of the Alpins vector analysis method.9,10 In an ideal correction, the TIA and SIA would be identical and the resulting difference vector would be 0. In the current study, the TIA was lower than the SIA, indicating slight overcorrection; however, no significant changes in SIA occurred during the follow-up, indicating that the SIA remained stable over time, which is consistent with findings in other toric IOL studies.12,26 Although Figure 7 shows that a mean difference vector of 0.3 at 83 degrees is present, Figure 8 visually describes that the range of the achieved correction (ie, correction index) varies between 0.46 and 1.77; 1.0 would correspond to the ideal postoperative result. Therefore, no overall recommendation
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regarding a possible surgeon adjustment can be given. The calculated correlations between the 3 fundamental vectors describe the overall success of the treatment, the potential overcorrection or undercorrection, and the misalignment of treatment.9,10 The correction index of 1.09 and the mean positive magnitude of error of 0.16 G 0.46 reflect slight overcorrection of the achieved astigmatic treatment. A possible explanation for the overcorrection could be underestimation of the toric IOL power at the corneal plane by the manufacturer, as previously described,27 or slight measurement errors using PCI-measured keratometry values that might have caused the slight overcorrection. Previous studies of vector analysis after implantation of other toric IOL models showed overcorrection23,28 as well as undercorrection.12,26 The angle of error indicates the misalignment of treatment. A positive angle of error value indicates a slight mean counterclockwise rotation to the intended axis and is consistent with reported rotation in previous studies.8,11,15,16,22–25 The mean angle of error remained stable over time, which agrees with findings in other toric IOL studies.12,28 The mean absolute angle of error was slightly higher than the rotation measured by comparison of the retroillumination photographs in the single-center subgroup analysis; however, this is less informative because of the limited number of patients in that subgroup. Further examinations comparing the angle of error and measured IOL rotation should be performed to provide a better understanding of the correlation and clinical interpretation. In addition, clinical parameters were correlated with vector analysis parameters. A strong negative correlation between the magnitude of difference vector and refractive cylinder in all postoperative visits could be seen, showing that a larger difference vector is associated with higher residual refractive cylinders. These findings were consistent with those of Ali o et al.12 using a different toric IOL model. Furthermore, the UDVA was correlated with the magnitude of difference vector, indicating that a larger difference vector negatively influences the UDVA. That eyes with a larger difference vector also had worse CDVA at the 1-week visit might be explained by higher amounts of higher-order aberrations in those cases, as hypothesized in literature. 12 However, this topic requires further study. In conclusion, implantation of the AT Torbi 709M IOL during cataract surgery seems to be a safe, effective, predictable, and stable procedure to correct regular corneal astigmatism.
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WHAT WAS KNOWN Implantation of the monofocal bitoric aspheric IOL used in this study is an effective procedure to correct preexisting corneal astigmatism within cataract surgery. WHAT THIS PAPER ADDS Refractive cylinder was reduced significantly, concurrent with visual improvement, by implantation of this toric IOL during routine cataract surgery. Vector analysis showed a small trend toward overcorrection that remained stable over time.
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129:1004–1008. Available at: http://archopht.jamanetwork. com/data/Journals/OPHTH/22540/ecs05116_1004_1008.pdf. Accessed December 11, 2014 JL, Pin ~ero DP, Toma s J, Plaza AB. Vector analysis of astig28. Alio matic changes after cataract surgery with implantation of a new toric multifocal intraocular lens. J Cataract Refract Surg 2011; 37:1217–1229
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EE/$FILE/AT_TORBI709Datasheet_GB_FINAL.pdf. Accessed December 11, 2014
OTHER CITED MATERIAL A. Carl Zeiss Meditec AG. TORBI 709, AT TORBI 709MP preloaded. Specifications. Available at: http://applications.zeiss.com/ C1257A290053AE30/0/538ECA28392347FDC1257A29005812
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First author: Eva M. Krall, MD Department of Ophthalmology, Paracelsus Medical University, Salzburg, Austria
