|Year : 2013 | Volume
| Issue : 3 | Page : 199-205
Long-term visual performance of AT LISA 909M multifocal toric intraocular lenses
Abdelrahman G Salman
Department of Ophthalmology, Ain Shams University, Cairo, Egypt
|Date of Submission||15-Mar-2013|
|Date of Acceptance||18-Mar-2013|
|Date of Web Publication||28-Feb-2014|
Abdelrahman G Salman
1195, Ain Shams University, Cairo
Source of Support: None, Conflict of Interest: None
The aim of the study was to analyze the subjective and objective visual and astigmatic effect of AT LISA 909M multifocal toric intraocular lenses (IOLs) for far and near vision after 1 year of implantation.
This is a prospective nonrandomized interventional case series.
After cataract surgery with implantation of AT LISA 909M multifocal toric IOLs, the visual, refractive, and corneal topographic outcomes, lens rotation, contrast sensitivity, and patient satisfaction were evaluated over 12 months and analyzed. Refractive astigmatic changes (target-induced astigmatism, surgically induced astigmatism, difference vector, magnitude of error, and flattening effect) were analyzed using the Alpins vectorial method.
The study enrolled 22 eyes (11 patients). Postoperatively, a significant reduction was observed in the refractive cylinder (P < 0.05) with an associated visual improvement in distance (P < 0.001) and near (P < 0.05) vision. Spectacle independency for distance and near vision was achieved in 95 and 90% of patients, respectively. After 1 year, significant stability of the IOL and patient satisfaction were observed for both distance and near vision. The Alpins correction index was +1.02.
The AT LISA 909M multifocal toric IOL resulted in long-term visual improvement in distance and near vision with good predictability in eyes with moderate-to-high corneal astigmatism undergoing cataract surgery.
Keywords: Multifocal, toric intraocular lens, vector analysis
|How to cite this article:|
Salman AG. Long-term visual performance of AT LISA 909M multifocal toric intraocular lenses. J Egypt Ophthalmol Soc 2013;106:199-205
| Introduction|| |
Visually significant astigmatism affects ∼15% of all patients undergoing cataract surgery . Refractive astigmatism is determined by corneal and lenticular components. Cataract surgery removes lenticular astigmatism but may unmask corneal astigmatism. Incisions made for phacoemulsification induce less astigmatism as incision size decreases ,.
Neutralization of corneal astigmatism during phacoemulsification gives these patients the opportunity for relative spectacle independence, which is the overall aim of refractive cataract surgery. These measures include placement of the main phacoemulsification wound on the axis, refractive keratotomy, laser refractive surgery, relaxing incisions at the limbus, and implantation of toric intraocular lenses (IOLs).
However, corneal incision procedures are relatively unpredictable, and laser refractive surgery may be associated with complications such as dry eyes, wound-healing problems, and infections ,,,.
Relaxing incisions at the limbus, although reliable, are only effective in patients with 1.5 D of corneal astigmatism and if incisions are closer to the visual axis and its effect is variable and unpredictable .
Monofocal toric designs are unable to compensate for the loss of accommodative ability after crystalline lens extraction and the subsequent visual deficit in intermediate and near-distance conditions. Therefore, the concept of combining multifocal and toric surfaces in an IOL to provide complete visual rehabilitation and achieve complete spectacle independence seems to be an optimal option for patients with cataract and significant corneal astigmatism .
Multifocal toric lenses have the potential for increased predictability provided they are placed accurately and do not rotate postoperatively ,.
The aim of our study was to analyze the subjective and objective visual effects of AT LISA 909M multifocal toric IOLs for distance and near vision after 1 year of implantation.
| Patients and methods|| |
Twenty-two eyes from 11 patients were enrolled in this prospective, nonrandomized, interventional case series.
The inclusion criteria were patients older than 40 years with visually significant cataract suitable for refractive lens exchange aiming for complete spectacle independence and with corneal astigmatism of 1.25 D or higher.
The exclusion criteria were patients with a history of glaucoma, retinal detachment, corneal disease, irregular corneal astigmatism, previous corneal surgery, keratoconus, abnormal iris, macular degeneration, retinopathy, neurophthalmic disease, or ocular inflammation.
Written informed consent was taken from all patients after explanation of the procedure and after obtaining approval from the medical and ethical committee.
All patients underwent a full ophthalmological examination including uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (Snellen chart), uncorrected intermediate visual acuity at 60 cm, uncorrected near visual acuity (Radner chart), manifest refraction, slit lamp examination, Goldmann applanation tonometry, corneal topography (Arlas 9000; Carl Zeiss Meditec, Berlin, Germany), biometry and keratometry (IOL Master v 5.2.1; Carl Zeiss Meditec), funduscopy, and corneal endothelial count with a specular microscope (SP-2000P; Topcon, Tokyo, Japan).
The following parameters were evaluated and recorded during the corneal topographic examination: K1, corneal dioptric power in the flattest meridian; K2, corneal dioptric power in the steepest meridian; KM, mean corneal power; and corneal astigmatism (calculated as the difference between K2 and K1).
The corneal keratometric and refractive data were sent to the lens company for calculation of the appropriate IOL power and axis of alignment. Suitable lenses were selected to neutralize both the sphere and the cylinder to achieve a postoperative spherical equivalent as close to zero as possible. The IOL manufacturer's calculator uses vector analysis of the keratometry-determined steep corneal axis and surgically induced astigmatism (SIA) to generate a target axis.
Vectorial analysis of astigmatic changes
The vector analysis of refractive astigmatic changes was performed with the Alpins vectorial method to compare preoperative and postoperative refractive astigmatism .
The following vectors were determined and evaluated: Target-induced astigmatism (TIA), which is the vector of intended change in cylinder for each treatment; SIA, which is the vector of the real change achieved; and the difference vector, which is the additional astigmatic change required to meet the intended target of the initial surgery. The difference vector is an absolute measure of success and is preferably zero. Overcorrection was defined as an SIA greater than the preoperative corneal astigmatism measured by keratometry.
In addition, the following parameters derived from the relationship between these vectors were calculated and analyzed at each postoperative visit:
- Magnitude of error, which is the arithmetic difference between the magnitudes of the SIA and the TIA. The magnitude of error is positive for overcorrection and negative for undercorrection.
- Angle of error, which is the angle between the SIA vector and the TIA vector. The angle is positive if the achieved correction is counterclockwise to the intended axis and negative if the achieved correction is clockwise to the intended axis.
- Correction index, which is the ratio of SIA to TIA. The ideal value would be 1, with values higher than 1 representing overcorrection and values lower than 1 representing undercorrection.
- Flattening effect, which is the amount of astigmatism reduction achieved by the effective proportion of the SIA at the intended meridian. A flattening effect was considered positive and a steepening effect was considered negative and is preferably 1.0.
- The index of success was calculated by dividing the difference vector by the TIA. This is a relative measure of success and is preferably zero.
Features of intraocular lens
We used AT LISA toric 909M (Carl Zeiss Meditec), which is aspheric multifocal toric, diffractive with a +3.75 D add, hydrophilic acrylic (25%) with a hydrophobic surface, having an optic diameter of 6.0 mm, a total diameter of 11.0 mm, lens design with a haptic angulation of °, single-piece four-plate haptics, and a refractive index of 1.46.
The toric component is on the anterior surface and the diffractive multifocal component is on the posterior surface. It can correct up to 12 D of cylinder. It has an incision size ranging from 1.5 to 1.8 mm depending on the power, a company-labeled A-constant 118.3, diopter ranging from −10.0 to +32.0 D sphere in increments of 0.5 D, and a cylinder ranging from +1.0 to +12.0 D in increments of 0.5 D.
Surgery was performed using a standard technique of sutureless microcoaxial phacoemulsification (Infiniti, Vision system, Alcon laboratories, Inc. Irvine, California, USA) under local anesthesia. Adequate dilatation was obtained with intracameral mydriasis. In all cases a 2.2 mm temporal corneal incision was made. Before starting the surgery, the axis was marked. After capsulorhexis creation and phacoemulsification, the IOL was inserted into the capsular bag using the reusable AT shooter A2-2000 injector (1.5 mm; Carl Zeiss Meditec) for IOLs having a spherical dimension ranging from −10.0 to +24.0 with a cylinder ranging from +1.0 to +4.0 and the single use AT smart cartridge set (1.8 mm; Carl Zeiss Meditec) for diopter range outside the previous range through the incision.
Three-step marking procedure for toric intraocular lens implantation :
- Horizontal axis marking: In the supine position three limbal reference marks are made at 3, 6, and 9 o'clock positions in the upright position at the slit lamp with a coaxial thin slit turned to 90-180° using a sterile marker. This avoids possible cyclorotation in the supine position during surgery.
- Alignment axis marking: Using the reference marks, the surgeon aligns a secondary device with the reference marks.
- Toric IOL alignment: The axis marks are used to delineate the steep axis of astigmatism upon which the IOL should be aligned. Then, standard capsulorhexis, hydrodissection, and phacoemulsification procedures are performed. The marks on the toric IOL indicate the flat meridian or plus cylinder axis of the toric IOL and should be aligned with the marked alignment axis.
First, gross alignment is achieved by rotating the IOL with a Sinskey hook clockwise while it is unfolding, until ∼20-30° of the desired position is achieved. It is important to remove the viscoelastic before rotating the IOL to the proper meridian. The IOL is then rotated to its final position under a balanced salt solution by precisely aligning the reference marks on the toric IOL with the limbal axis marks .
All patients received a 4-week course of topical therapy including a combination of topical antibiotic and steroid started q.i.d. with gradual tapering.
Patients were evaluated postoperatively on day 1, at 1 month, and at 3, 6, and 12 months after surgery. On day 1 only UDVA, tonometry, and the integrity of the anterior segment were evaluated. On other follow-up days, evaluation was identical to the preoperative evaluation.
Contrast sensitivity was measured with the CSV1000E test (Good-Lite, Elgin, Illinois, USA), using sine-wave grating charts to measure spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd). The CSV1000E test has been used in several studies and has been shown to give reliable, repeatable, contrast sensitivity function scores .
All measurements were taken under photopic conditions at 85 cpd/m 2 and under mesopic conditions at 5 cpd/m 2 . According to Wachler and Krueger  the contrast sensitivity values were normalized using the ratio between a patient's result and the normal score for the patient's age group. Scores higher or lower than 1.0 indicated contrast sensitivities higher or lower than expected.
Postoperative intraocular lens stability and rotation
At the slit lamp with rotating slit to confirm optimal alignment and ensure no postoperative IOL rotation had occurred. As the IOL marks are located at the periphery of the IOL optic, full mydriasis of the pupil is required. Realignment of a rotated toric IOL should ideally be performed as soon as possible and preferably before 2 postoperative weeks because of the formation of adhesions between the capsular bag and IOL optics. Misalignment of the IOL was defined as the mean difference between the axis of the internal astigmatism and the preoperative orientation of the steepest corneal meridian, and a misalignment of more than 10° is considered the indication for realignment ,.
The patients were asked to fill out a questionnaire that included questions regarding patient satisfaction.
All complications were recorded. In the event of a complication during surgery that might compromise the stability of the toric IOL, such as zonular damage, vitreous loss, capsulorhexis tear, or capsular rupture, conversion to a standard nontoric IOL was required and the case was excluded from the study.
All data were recorded in preformatted data collection forms and analyzed using SPSS version 17.0 (SPSS Inc., Chicago, Illinois, USA). The Student t-test was used for paired data and the results were considered statistically significant when P values were less than 0.05 and highly significant when P values were less than 0.001.
| Results|| |
Twenty-two eyes from 11 patients were studied. Six (54.5%) were male patients and five (45.5%) were female. The mean age was 52.68 ± 12.4 years.
Refractive data preoperatively and 1 year postoperatively are summarized in [Table 1].
|Table 1: Summary of preoperative and 1-year postoperative refractive data|
Click here to view
The mean preoperative refractive cylinder was 2.69 + 0.32 D and postoperative mean was 0.68 + 0.58 D (range 0.00-1.0 D). The residual refractive astigmatism of 1.0 D or less was achieved in almost all eyes, which showed a statistically highly significant reduction in the refractive cylinder (P < 0.001). No significant changes were observed in corneal astigmatism (P = 0.32).
Preoperative mean was −3.52 ± 1.12 and postoperative mean was +0.42 ± 0.23 D (range −0.75 to +1.50).
Other refractive measures
The mean spherical power of the implanted IOL was+20.62 ± 8.32 D and its mean cylindrical power was 2.99 ± 1.65 D.
Contrast sensitivity levels were high. Approximately 20% of patients reported moderate glare and halos.
Spectacle independency for distance and near vision was achieved by 95 and 90% of patients, respectively, both of which were highly significant (P < 0.001).
Vector changes in refractive astigmatism
The mean magnitude of the TIA was 2.53 ± 1.15 D; the mean magnitude of the SIA was always slightly higher at 2.91 ± 1.14 D. The difference between the TIA and the SIA was statistically significant only at 3 months (P < 0.05) but not statistically significant at 1-year follow-up (P > 0.05). The mean magnitude of error was positive (overcorrection) and close to zero at all postoperative visits (0.07 ± 0.33, 0.26 ± 0.48, and 0.16 ± 0.51 D at 1, 3, and 12 months, respectively). No significant changes in this parameter were observed during the follow-up (P > 0.05). The mean correction index was 1.04 ± 0.12, 1.05 ± 0.15, and 1.02 ± 0.25 at 1, 3, and 12 months, respectively. This parameter did not change significantly during the follow-up (P > 0.05). Other data are presented in [Table 2] and [Figure 1].
Intraocular lens stability and patient satisfaction
The mean postoperative total error in toric IOL alignment was 4.9 ± 2.1°. Significant stability of the IOL was observed at the final postoperative visit (12 months). Ninety percent of IOLs were aligned within 5° of the astigmatic axis and 100% were within 10° of the target. None of the IOLs required surgical repositioning.
Significant patient satisfaction (95%) after 1 year was observed for distance and near vision.
Postoperative complications were mean endothelial cell loss of 2.4% at 1 month and 4.7% at 1 year (preoperative mean endothelial cell density was 2.954 + 214 cells/mm 2 and postoperative mean endothelial cell density was 2862 ± 124 and 2.797 ± 197 cells/mm 2 at 1 and 12 months, respectively), which was statistically insignificant (P > 0.05). Posterior capsular opacification (PCO) was seen in two eyes (0.91%) after 12 months for which a YAG laser capsulotomy was performed, with a successful visual impact with no effect on IOL rotation.
During the follow-up period no significant decentration, no adhesions with the iris, no pupillary capture, no infection, no significant overcorrection or undercorrection as regards the target postoperative refraction was observed.
| Discussion|| |
The importance of independence from glasses should not be undervalued. Toric IOL has been shown to be very effective for the compensation of pre-existing corneal astigmatism in eyes undergoing cataract surgery. However, this IOL can only improve distance visual acuity with spectacle dependence for near vision. A new model of diffractive multifocal IOLs with a toric component was introduced to compensate for any degree of corneal astigmatism and allow spectacle independence ,,,,,.
One aspect to consider when calculating a toric IOL is the vector change in corneal astigmatism induced by the surgery itself. The expected amount of SIA must be incorporated into the toric IOL power calculation to select the most appropriate toric IOL model and alignment axis. However, the amount of SIA is difficult to predict and depends on several factors such as the location and size of the incision ,.
In our study we performed sutureless microcoaxial phacoemulsification through a 2.2 mm temporal corneal incision in all cases.
The 2.2 mm incision had been shown to induce an SIA of 0.2-0.3 D for temporal incisions and 0.4 D for superior incisions ,,. Similar results have been observed for sub-2.0 mm incisions  in comparison with incision sizes of 2.8-3.2 mm, which have been shown to induce an SIA of 0.4-0.8 D for temporal incisions, 0.6 D for superior incisions, and 0.9-1.2 D for on-axis incisions ,.
Vector analysis is used to determine the amount of astigmatism reduction achieved at the intended meridian of treatment . Three fundamental vectors are used in this analysis: TIA, SIA, and the difference vector. The various relationships between the three vectors provide a complete description of the astigmatic correction achieved with a specific modality of treatment . In our study we found a statistically insignificant difference between the magnitudes of the TIA and SIA vectors; the difference was statistically significant at 3 months only. There were no statistically significant differences in the SIA between follow-visits after 1 year (P > 0.05).
The mean magnitude of error was positive (overcorrection) and close to zero at all postoperative visits and no significant changes in this parameter were observed during the follow-up (P > 0.05). This small, not clinically relevant, trend toward overcorrection was different from the trend toward undercorrection found with monofocal toric IOL models when evaluated using the Alpins method (Acri.Comfort 646 TLC, mean magnitude of error −0.36 D; Acrysof toric, mean magnitude of error −0.34 D) ,.
This overcorrection may have been the result of the combination of small misalignments of axis (either surgical inaccuracies or secondary to postoperative rotation). This was confirmed with the significant and positive correlation between the magnitude of difference vector and the absolute angle of error at all postoperative visits. The larger the difference vector, the more significant the absolute angle of error. Rotation of the toric IOL of 3° leads to residual astigmatism of 10% of the initial power ,,, whereas variation of 100 μm in axial length translates to 0.28 D of variation in the chosen power of the spherical lens .
Furthermore, there were no significant changes in the magnitude of error or in the correction index during the follow-up, which confirms the stability of the predictable astigmatic correction achieved with the AT LISA 909M multifocal toric IOL.
Marking in upright position is important as cyclotorsion of the eye from the upright to supine position is ∼2-4° on average, but can be up to 15° in individual patients ,,.
In our study there was a significant visual improvement in distance vision (P < 0.001). Ninety-eight percent of eyes achieved a UDVA of 6/12 or better and 78% of patients achieved a UDVA of 6/9 or better. Improvement in corrected distance visual acuity was statistically significant (P > 0.05). This is comparable to the results of other studies involving the same IOL during short-term follow-up ,, as well as to the results of other types of multifocal toric IOLs such as Rayner M-flex T , AcrySof IQ ReSTOR Multifocal toric IOL , and M plus toric Oculentis IOLs .
The significant decrease in the refractive cylinder found in our study was consistent with reports on other toric IOLs [9-12] and multifocal toric IOLs ,,,,,.
In our study there was a statistically significant improvement in both near and intermediate vision (P < 0.05), which was consistent with the results of other studies ,,,,,.
Complete spectacle independence was achieved in 95% of patients for distance vision and in 90% of patients for near vision, which was highly significant (P < 0.001). This was consistent with the results of Visser et al.  in whose study spectacle independency for distance and near vision was achieved by 95 and 79% of patients, respectively, with AT LISA 909M IOL on 3 months' follow-up.
The residual refractive astigmatism of 1.0 D or less was achieved in ∼90% of eyes, which was a statistically significant reduction in refractive cylinder (P < 0.05). No significant changes were observed in corneal astigmatism (P = 0.32); this was consistent with the results of Visser et al.  and Mojzis et al.  on the same type of IOL in the short term and with the results of studies on other types of multifocal toric IOLs ,,,.
In our study significant patient satisfaction after 1 year (95%) was seen for distance and near vision. Significant stability of the IOL was present, and at the final postoperative visit after 1 year 90% of IOLs were aligned within 5° of the astigmatic axis and 100% were within 10° of target. None of the IOLs required surgical repositioning; this was comparable to the results of other studies in different types of IOLs ,,.
In comparison with the stability of other acrylic toric IOLs, the overall cumulative incidence of surgical repositioning in the previous studies was: 0.3% for ReSTOR Multifocal Toric IOLs , 2.1% for Rayner M-flex T  IOLs, and 0% for Acri.LISA toric IOLs ,,. However, it was higher for silicone toric IOLs such as STAAR toric IOLs, as in the literature its repositioning was up to 6.6% ,.
No statistically significant change in K1, K2, or KM were observed (P < 0.05), as these reflect corneal parameters that did not change postoperatively after 1 year of follow-up.
Contrast sensitivity levels were high. Approximately 20% of patients reported moderate glare and halos, which did not affect their final visual acuity.
A PCO of 0.91% (two eyes) was found after 12 months with a successful visual impact with no effect on IOL rotation. In the majority of studies on toric acrylic IOL, PCO did not compromise the visual outcome, and a neodymium: YAG posterior capsulotomy was not required ,.
Silicone IOLs were associated with lower PCO rates compared with acrylic IOLs, but this difference did not reach statistical significance .
Thus, it is seen that AT LISA 909M multifocal toric IOLs can restore distance and near visual function in eyes with cataract and moderate-to-high corneal astigmatism. They provide excellent predictability for the correction of refractive astigmatism. However, a larger multicenter study is required for better evaluation.
| Acknowledgements|| |
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]