Rotational Stability of Monofocal and Trifocal Intraocular Toric Lenses With Identical Design and Material but Different Surface Treatment

PURPOSE
To compare the rotational stability, total misalignment, and visual and refractive outcomes achieved with a trifocal toric versus a monofocal toric intraocular lens (IOL).


METHODS
In this prospective, interventional case series, eyes of patients consecutively scheduled for cataract surgery who had clinically relevant astigmatism were implanted with a FineVision Pod FT trifocal toric IOL or an Ankoris monofocal toric IOL (both PhysIOL SA, Liège, Belgium). Certain comorbidities, such as pseudoexfoliation syndrome, were allowed. IOL rotation and total misalignment were analyzed 15 minutes, 1 day, 1 week, 6 weeks, 6 months, and 1 year postoperatively.


RESULTS
Seventy-one eyes of 53 patients were assessed: 37 eyes were implanted with the trifocal IOL and 34 eyes with the monofocal IOL. More IOL rotation occurred in the monofocal group compared to the trifocal group (mean 4.23° ± 4.64° vs 2.55° ± 2.62°; P = .043, 12 months). Mean total misalignment was higher in the monofocal group (6.67° ± 6.59° at 12 months vs 3.79° ± 3.59° in the trifocal group) (P = .017). Postoperatively, more eyes achieved a refractive cylinder of 0.50 diopters or below in the trifocal group (65% at 12 months) than in the monofocal group, even in the monofocal subgroup analysis that excluded keratoconic eyes (42% at 12 months; P = .009).


CONCLUSIONS
The monofocal and trifocal toric IOLs both appear to effectively reduce refractive astigmatism and provide good visual acuity in astigmatic patients having cataract surgery. The trifocal toric IOL offers better rotational stability than the monofocal IOL, probably due to the higher frictional coefficient of its surface. [J Refract Surg. 2018;34(2):84-91.].


Rotational Stability of Two IOLs/Vandekerckhove
Helsinki and approved by the local ethics committee.All patients provided written informed consent.
Inclusion criteria were cataracts and coexisting total corneal astigmatism greater than 1.00 D oblique or withthe-rule [WTR] or greater than 0.75 D against-the-rule [ATR].The patient's desire to be independent of reading glasses and the absence or presence of the exclusion criteria below determined whether a monofocal (Ankoris) or trifocal (FineVision Toric, Pod FT) toric IOL was implanted.Exclusion criteria for the trifocal toric group were irregular astigmatism, amblyopia, corneal disease, macular disease, or any ophthalmic pathology that could negatively affect postoperative visual acuity or contrast vision.
Exclusion criteria for monofocal toric IOL implantation were severe ophthalmic pathology with a major impact on visual function, such as corneal scarring, glaucomatous visual field defects, advanced macular disease, and corneal astigmatism with a predominantly irregular component.
In contrast to many refractive cataract surgery clinical studies, the current study assessed a "real life" patient population. 13Specifically, eyes with pseudoexfoliation syndrome or slight macular gliosis were enrolled in both groups.Pseudoexfoliation syndrome has been identified as a risk factor for IOL rotation.Other conditions (gliosis, amblyopia, and keratoconus) can affect visual acuity.Eyes with stable keratoconus or amblyopia were enrolled in the monofocal group alone.

iOLS
Figures A-B (available in the online version of this article) show the study IOLs.The Ankoris is a monofocal toric IOL consisting of hydrophilic acrylic material.The biconvex aspheric optic is aberration correcting (-0.11  µm).This lens has an optic body diameter of 6 mm, overall diameter of 11.4 mm, and haptics with a double Cloop design and 5° angulation.The FineVision Toric Pod FT is a trifocal toric IOL with the same material characteristics and dimensions as the Ankoris.It has +1.75 D addition for intermediate, +3.50 D for near vision, and an unpolished surface.It also has diffractive rings on its anterior surface.The Ankoris has a polished surface.

PreOPerative aSSeSSment
Preoperatively, all patients underwent full ophthalmic examination, including refraction and corrected distance visual acuity (CDVA).Optical biometry and corneal topography were performed using the Galilei G6 Lens Professional (Ziemer, Port, Switzerland).IOL spherical power was calculated using the SRK/T, Hoffer Q, Holladay I, or Haigis formula, depending on axial length and anterior chamber depth.IOL cylinder power and target IOL axis were calculated using the online Ankoris and FineVision Toric Calculator (PhysIOLtoric, Toric IOL Calculator, version 3.6.6;http://www.physioltoric.eu), based on total corneal (ray-traced) astigmatism.The main incision was planned on the steep corneal meridian in all cases, independent of the axis of astigmatism.A surgically induced astigmatism of 0.40 D was assumed to err on the side of undercorrection of the corneal astigmatism and avoid flipping the axis of astigmatism.Target refraction was emmetropia in the trifocal group.In the monofocal group, emmetropia was targeted in 28 of the 34 eyes.The goal for three eyes with keratoconus was partial correction (two-thirds) of preexisting corneal astigmatism.In three other eyes, the target refraction was myopia.
To account for differences in preexisting ocular comorbidities and targeted refraction, two monofocal toric IOL subgroups were defined and used for comparisons with the trifocal toric IOL group.Monofocal subgroup 1 (for comparison of uncorrected distance visual acuity [UDVA]) excluded amblyopic eyes and keratoconic eyes with intended postoperative myopia.Monofocal subgroup 2 (for comparison of postoperative refractive cylinder) excluded three keratoconic eyes, given the residual cylinder in studies including keratoconic eyes was mostly higher than in those excluding them.All eyes in the trifocal and monofocal groups were available for rotational stability analysis.

SurgicaL technique
An experienced surgeon (KV) performed all surgeries using a standard phacoemulsification technique with a 2.2-mm limbal incision on the steep corneal meridian.With the patient seated to prevent cyclotorsion, the target IOL axis was marked using a pendulum marker (ToMark corneal marker; Geuder, Heidelberg, Germany). 14 preloaded capsular tension ring (Morcher Easyring 14c, 11 mm; Morcher, Stuttgart, Germany) was injected into the capsular bag.A capsular tension ring was used in all cases to allow for more homogenous capsular shrinkage and therefore less decentration, rotation, and tilt postoperatively.The IOL was implanted using the Monarch C injector (Alcon Laboratories, Inc., Fort Worth, TX) after enlarging the main incision (maximal 2.3 mm) by re-entering the incision with the 2.2-mm clear cornea knife.After complete aspiration of viscoelastic anterior and posterior to the IOL, the IOL was aligned with the corneal markings.Clockwise and counterclockwise finetuning of the lens was permitted by the symmetrical shape of the IOLs (double C-loop haptics).Postoperative therapy consisted of tobramycin/dexamethasone and nepafenac.

POStOPerative aSSeSSment
Postoperative examinations were performed at 15 minutes, 1 day, 1 week, 6 weeks, 6 months, and 12 months.The actual IOL axis was assessed from images taken with the Galilei 6 frontal (black/white) camera, which also captures the Placido rings, showing the IOL axis marks, optic edge, haptics, and iris landmarks, as shown in Figure CB, available in the online version of this article).The images were imported into a Keynote file (version 6.6.1;Apple, Inc., Cupertino, CA) and rotational stability was analyzed according to a protocol modified after Maedel et al. 15 Each frontal image was superimposed with a sketch of the IOL.The IOL sketch consisted of 0.25 pixel lines drawn in Keynote: two straight parallel lines touching the IOL axis marks on each side, and several easily recognizable IOL elements (optic and haptics edges, optic center, and the six round IOL axis marks [Figure CA]).
Each frontal image was magnified to match the size of the sketch (Figure CC).The position and axis of the IOL sketch were adjusted to the corresponding elements on the frontal image.To correct for head malpositioning and/or eye cyclotorsion during image recording, two to three peripheral iris landmarks were used as reference points throughout all study visits.All frontal images were assessed twice.In case of discrepancy (> 1°) between the two assessments, the frontal image was analyzed a third time and this result was used.
Absolute misalignment was defined as the difference between the target and actual IOL axis at any postoperative time.Rotation was defined as the difference in IOL axis at 15 minutes and any given postoperative time.Vector analysis was used for postoperative astigmatism analysis. 16

miSSing data handLing and StatiSticaL anaLySiS
For the primary study outcome (rotational stability and residual astigmatism), the last observation carried forward (LOCF) method was used for missing data resulting from missed visits or inability to perform an accurate measurement.The LOCF method was also used for one eye that underwent secondary surgery (IOL repositioning) to minimize bias, which would artificially favor rotational stability.The LOCF method was not used for the secondary study outcome (visual acuity).
Statistical analysis was performed using R software for statistical computing (Team RC.R: a Language and Environment for Statistical Computing).Normal distribution and homogeneity of variances were tested via Shapiro-Wilks and Bartlett's tests, respectively.If both tests were not significant, the P value of the t test was calculated, otherwise the non-parametric Wilcoxon signed rank test was used.A P value of less than .05was considered statistically significant.All statistical tests were performed as two-sided tests, except for the comparison between the trifocal and monofocal group for lens rotation and total misalignment, where onesided tests were used based on the assumption that these parameters are lower for the trifocal group, given the presumed higher frictional coefficient of its lens surface and preliminary clinical observations.
Correlation analysis was performed with Pearson's correlation coefficient for continuous variables or with the Wilcoxon signed-rank test for discrete variables.A longitudinal discrete mixed model (generalized estimating equation) was used to compare the percentage of eyes with a residual cylinder of 0.50 D or less. 17

RESULTS
Fifty-three consecutive patients had monocular or binocular implantation of a monofocal (n = 34 eyes) or trifocal (n = 37 eyes) toric IOL.Table 1 summarizes the preoperative demographic data for all study eyes.No differences were seen in the mean preoperative axial length and white-to-white distance of the monofocal and trifocal groups.
Although no difference was observed in the mean spherical IOL power of both groups, cylindrical IOL power was greater in the monofocal group (P = .008).Overall, 8.5% of all eyes had pseudoexfoliation syndrome (n = 6 eyes, 2 in the monofocal group, 4 in the trifocal group).There were 9 amblyopic eyes and 3 keratoconic eyes with reduced spectacle-corrected visual acuity in the monofocal group.
The LOCF method was used in 7 eyes for the analysis of rotational stability and residual astigmatism.The LOCF method was applied for missing data at a single visit (month 6 or 12) in 6 eyes and for all visits after week 1 in 1 eye.The latter eye underwent secondary surgery (IOL repositioning) after the week 1 study visit because of significant early rotation (16°) and misalignment (22°).

viSuaL acuity
As shown in Table A (available in the online version of this article), UDVA in the trifocal group was comparable to UDVA in the monofocal subgroup 1 (excluding amblyopic eyes, keratoconic eyes, and eyes with intended myopia) at 6 weeks, 6 months, and 12 months.

refractive cyLinder
As shown in Table 2, better refractive astigmatism outcomes were observed among the trifocal IOL group than in the overall monofocal or monofocal subgroup 2 (excluding the 3 keratoconic eyes) at all visits.The percentage of eyes with postoperative refractive astigma-Rotational Stability of Two IOLs/Vandekerckhove tism of 0.50 D or below fell over the 12-month follow-up period in all groups.
Figure D (available in the online version of this article) shows the preoperative corneal and 12-month postoperative refractive cylinder for the trifocal group and monofocal subgroup 2, via single-angle plots. 16The preoperative corneal cylinder ranged between 0.83 and 3. 28    1B-1D).

POSteriOr caPSuLar fibrOSiS
Capsular fibrosis requiring YAG capsulotomy at postoperative month 12 occurred at a similar rate (approximately 1 in 3 eyes) among the monofocal and trifocal groups.

factOrS infLuencing rOtatiOnaL StabiLity
As shown in Figure E (available in the online version of this article), capsular fibrosis was the only variable that showed significant correlation with 12-month rotational stability (P = .011),with worse rotational stability seen among eyes scheduled for (or having undergone) laser capsulotomy.

DISCUSSION
The current study assessed the visual outcomes and rotational stability of a new trifocal and monofocal toric IOL platform.To our knowledge, this is the first study comparing rotational stability of two IOLs with identical design and material, but with a different surface treatment.
Excellent refractive results were also seen, with a refractive cylinder of 1.00 D or below in 94% of eyes and 0.50 D or below in more than half of the eyes (42% in the monofocal subgroup 2 and 65% in the trifocal group) at 12 months.This (clinically) small difference can be explained partly by the higher IOL rotation observed with the monofocal IOL and partly by the higher preoperative corneal astigmatism in the monofocal group.
Twelve-month postoperative IOL rotation and total misalignment outcomes compare favorably with those reported in the literature, despite including eyes with comorbidities such as pseudoexfoliation syndrome in the current study. 13,20Although the two Rotational Stability of Two IOLs/Vandekerckhove toric IOLs showed good long-term rotational stability overall, early misalignment reached 10° or more within 1 week in 6 eyes, with surgical repositioning needed in 1 eye.Four methodological features allowed in-depth and robust analysis of rotational stability in the current study.First, outcomes were assessed over 12 months, with a total of six assessments of IOL alignment.1][22][23] Our data showed that, for this particular toric IOL platform, rotation mainly occurred in the first 6 months and then leveled off.
Second, a "real life" patient population including eyes with comorbidities that may affect IOL rotational stabil-ity or visual acuity, such as pseudoexfoliation syndrome or keratoconus, was used, unlike most other studies. 13hird, we accounted for the effect of head malpositioning and cyclorotation on the accuracy of the assessment of the IOL alignment.In a series of 500 measurements of toric IOL alignment, a mean difference of 1.0° ± 0.9° (P = .02)was observed between assessment with correction for cyclotorsion and head position versus uncorrected assessment; in 17% of measurements, the error reached 2° or more. 24ourth, immediate postoperative IOL misalignment was captured by recording the IOL position 15 minutes after surgery, allowing "rotation" to be differentiated from "total misalignment," as defined in the method- ology section.Although IOL rotation relates solely to IOL stability within the capsular bag, total misalignment from the intended axis arises from preoperative corneal marking error, inaccurate IOL alignment with the corneal markings intraoperatively, and rotation, starting within minutes after implantation.
Unsatisfactory IOL rotational stability has been discovered years after launch of new toric IOLs, 13,15,25 a scenario observed even with lenses that were strikingly similar but not identical in shape to existing toric IOLs with proven rotational stability. 15A recent study revealed differing levels of rotational stability between IOLs with identical designs, but different materials. 26he findings of the current study demonstrated better rotational stability and less total misalignment with the trifocal than the monofocal toric IOL despite an identical shape and IOL material.It is therefore likely that the difference in rotational stability is due to their differing surfaces.Lens surface adhesiveness is thought to be an important factor contributing to rotational stability, especially during the first few postoperative days, before capsular bag shrinkage occurs.We think that interaction between the IOL and capsular bag depends not only on IOL material, 27 but also on IOL surface treatment.The trifocal FineVision lens has an unpolished surface with anterior diffractive rings, whereas the monofocal Ankoris lens has a polished surface.Because rough surfaces produce greater friction, and the presence of friction inhibits rotation, the different surface may explain the difference in rotational stability and total misalignment.
Other factors, including incision integrity, residual viscoelastic, and intraocular pressure, may affect rotational stability.However, the current study went to great lengths to mitigate the influence of these confounders through surgical standardization.
The rotational stability of the three keratoconic eyes (12-month rotation: 1° to 3°, total misalignment 1° to 4°) was not different from the non-keratoconic eyes in the monofocal group.This finding is consistent with previous studies, 28 which have demonstrated similar rotational stability in keratoconic eyes compared to studies in eyes with regular astigmatism.Given the fact that the three keratoconic eyes exhibited reduced spectacle-corrected visual acuity and that we only aimed for partial correction (two-thirds) of corneal astigmatism in the three keratoconic eyes, they were not included in the analysis of visual acuity (monofocal subgroup 1) and residual cylinder (monofocal subgroup 2).
The main limitation of the current study is its small size (71 eyes), especially regarding the comparison between the monofocal and trifocal groups.However, because the findings consistently show a significantly different rotational stability of the two IOLs over 12 months, it appears that the current study results are noteworthy.Further clinical studies and in vitro research are required to build on the findings made in the current study.
This prospective interventional case series assessing the trifocal FineVision IOL and the monofocal Ankoris IOL showed that both toric IOLs provide good visual acuity and rotational stability in astigmatic patients having cataract surgery.The trifocal toric IOL offers better rotational stability and less total misalignment than the monofocal toric IOL, which may be due to the different frictional coefficient of its lens surface.Further research is required to determine the impact of the lens surface treatment on rotational stability.

Figure 1 .
Figure 1.(A) Lens rotation and total misalignment for the total study group.(B) Lens rotation for the trifocal and monofocal groups (mean values).(*) P < .05. (C) Total misalignment for the trifocal and monofocal groups (mean values).(*) P < .05. (D) Total misalignment for the trifocal and monofocal groups, 12 months postoperatively.The rectangles represent the 25th and 75th percentiles.The thick lines represent the median values, the dashed lines the mean values.The whiskers represent the maximum and minimum values excluding outliers.The dots represent the individual date (eyes).(*) P < .05.The FineVision and Ankoris lenses are manufactured by PhysIOL SA, Liège, Belgium.

Figure
Figure C. (A) Image of the trifocal toric intraocular lens (IOL) with overlying sketch used to evaluate rotational stability.(B) Postoperative frontal image (Galilei 6 Lens Professional; Ziemer, Port, Switzerland).Blue arrows indicate IOL axis marks, red arrows indicate investigator-defined iris landmarks.(C) Postoperative frontal image (Galilei 6), superimposed with IOL sketch after adjusting position and angle.

Figure D .
Figure D. (A) Single-angle polar plot of preoperative ray-traced corneal astigmatism and postoperative refractive astigmatism (total study group with the 3 keratoconic eyes excluded).Each circle represents 1.00 diopter (D) of cylinder (cyl).(B) Singleangle polar plot of preoperative ray-traced corneal astigmatism for the trifocal and monofocal (subgroup 2) groups.Each circle represents 1.00 D of cylinder.(C) Single-angle polar plot of postoperative refractive astigmatism for the trifocal and monofocal (subgroup 2) groups.Each circle represents 0.50 D of cylinder.(*) The central data points (0.00 D) are not visualized.In the trifocal and monofocal (subgroup 2) groups, 13 data points (35% of eyes) and 6 data points (19% of eyes) are at 0.00 D, respectively.SD = standard deviation

TABLE 1
Preoperative Patient Demographics According to Main IOL Groups and Monofocal IOL Subgroups IOL = intraocular lens; SD = standard deviation a Versus trifocal.bExcludingamblyopicpatientsandpatients with keratoconus or intended postoperative myopia.cExcludingpatientswithkeratoconus.dWilcoxonranked-sumtest.eStatisticallysignificantdifference.fttest.rotation was 3.35° ± 3.79° and total misalignment was 5.17° ± 5.40° after 12 months.One eye (monofocal IOL) required secondary surgery for IOL rotation.The impact of different IOL surfaces on rotation and total misalignment was analyzed by comparing the trifocal and monofocal groups (TableB).Mean IOL rotation and mean total misalignment were smaller in the trifocal than in the monofocal group at all postoperative visits (TableB, Figures

TABLE 2
Postoperative Refractive Cylinder and Percentage of Eyes With ≤ 0.50 D D = diopters; cyl = cylinder; SD = standard deviation a Versus trifocal.b Wilcoxon ranked-sum test.c Statistically significant difference.d t test.e Linear mixed generalized estimating equation models to analyze longitudinal profile.

TABLE A
Postoperative UDVA (logMAR) UDVA = uncorrected distance visual acuity; SD = standard deviation a Versus trifocal.b Wilcoxon ranked-sum test.c Statistically significant difference.d t test.

TABLE B
Postoperative Lens Rotation and Total Misalignment for Total Study Cohort and Trifocal and Monofocal Groups N/A = not applicable; SD = standard deviation a Trifocal versus monofocal.b Wilcoxon ranked-sum test (one-sided).c Statistically significant difference.