Intraocular lens alignment methods

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1 REVIEW C URRENT OPINION Intraocular lens alignment methods Praneetha Thulasi a, Sumitra S. Khandelwal b, and J. Bradley Randleman a,c Purpose of review This article reviews current concepts in intraocular lens alignment strategies to maximize intraocular lens (IOL) positioning. Recent findings A variety of strategies has been developed to maximize toric IOL position, including preoperative calculators to determine the appropriate IOL power and orientation, intraoperative alignment devices, and postoperative software to determine if IOL rotation would be beneficial for refractive outcomes. Summary The combination of using multiple toric IOL calculators and intraoperative alignment devices has improved toric IOL outcomes. The relationship of the posterior corneal power and its effect on outcomes remains to be fully elucidated. Postoperative IOL rotation may be necessary even when the IOL is aligned as planned because of surgically induced astigmatism. Keywords intraoperative aberrometry, intraocular lens alignment, toric intraocular lens, toric intraocular lens calculators INTRODUCTION An increasing number of patients undergoing cataract surgery expect spectacle independence. Up to 20 30% of patients undergoing cataract surgery have at least 1.25D of astigmatism [1]. Astigmatism of 0.75D or greater will frequently compromise distance visual acuity with diffractive multifocal intraocular lenses (IOLs), highlighting the need to incorporate astigmatic correction as an essential part of any refractive cataract surgery [2]. Although there are many ways of minimizing astigmatism, toric IOLs play a key role in achieving emmetropia. When comparing bilateral toric lens implantation to aspheric controls, 84% achieved spectacle independence versus 31% in the control group, highlighting the effectiveness of toric IOLs [3 && ]. This review discusses preoperative assessment of corneal astigmatism, IOL options, intraocular alignment of toric lenses, and postoperative considerations and revision of misaligned IOLs. more fibronectin adhesions than silicone or PMMA IOLs [4,5]. This, along with other in-vitro studies, suggest that hydrophobic acrylics had the most adhesive properties, with silicone IOLs having the least adhesive properties [4,5]. These impact surgical technique in regards to rotating the toric in position and postoperative stability of the lens. Toric IOLs also have different lens and haptic designs, each with different stability within the bag. Larger diameter lenses (11.2 mm) have more rotational stability than shorter diameters lenses (10.8 mm) in the bag [6]. When comparing haptic design, loop-haptic silicone lenses are more stable compared with plate-haptic silicone lenses. However, plate-haptic and loop-haptic acrylic lenses did not show any difference in rotational stability [7]. Toric IOLs can be either spheric or aspheric. Perez-vives et al. showed that although the optical quality was better with spheric toric IOLs with a TORIC LENS PROPERTIES Toric IOLs range in materials from hydrophobic and hydrophilic acrylic, silicone, and poly methyl methacrylate (PMMA) biomaterials. Each biomaterial has different degrees of IOL-bag adhesions, thus affecting lens stability within the bag. Human autopsy eyes in those with acrylic IOLs had significantly a Department of Ophthalmology, Emory University, Atlanta, Georgia, b Baylor College of Medicine, Cullen Eye Institute, Houston Texas and c Emory Vision, Emory Eye Center, Atlanta, Georgia, USA Correspondence to J. Bradley Randleman, 5671 Peachtree Dunwoody Road, Suite 400, Atlanta, GA 30342, USA. Tel: ; fax: ; jrandle@emory.edu Curr Opin Ophthalmol 2016, 27:65 75 DOI: /ICU Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved.

2 Cataract surgery and lens implantation KEY POINTS Astigmatic correction with toric intraocular lens implantation is a key part of modern refractive cataract surgery. Posterior corneal astigmatism needs to be taken into account while selecting a toric intraocular lens. Multiple nomograms adjust for this and other factors that influence astigmatic correction with toric lenses. Newer tools such as intraoperative aberrometry hold promise in refining toric alignment, although more research is needed to assess their effectiveness. larger pupil, it led to more corneal positive spherical aberrations overall, leading to better optical quality with aspheric IOLs than spheric toric IOLs [8 & ]. All available toric IOLs in the United States are aspheric in design. LENSES REQUIRING ALIGNMENT All toric IOLs are by definition acutely sensitive to appropriate alignment. This includes monofocal toric, multifocal toric, and pseudo-accommodative toric IOLs. Monofocal toric lenses are designed to correct astigmatism along with a specific myopic or hyperopic correction. These lenses come in various materials, lens designs, and diameters, with the ability to correct various astigmatic values, from 0.5 to 12D. Table 1 lists the basic properties of toric IOL models available in the United States. Multifocal toric lenses allow astigmatic correction combined with correction of spherical error and presbyopia. Currently there are no FDAapproved multifocal toric lenses in the United States, although IOLs covering the same toric correction range as their monofocal toric IOL counterparts appear to be nearing FDA approval. Outside the United States, a variety of additional multifocal toric IOLs are available with wider ranges of toric correction. In patients with moderate levels of astigmatism, toric multifocal lenses (ReSTOR SND1T, Alcon, Fort Worth, Texas, USA) had better uncorrected near and intermediate vision than toric monofocal lenses (Acrysof SN6AT, Alcon) [9]. Trulign (Bausch & Lomb, Rochester, New York, USA) is the only approved toric pseudo-accommodating lens in the United States, available as a silicone lens with the potential to reduce to correct presbyopia and improve distance correction. Trulign corrects three cylindrical powers 1.25, 2.00, and 2.75D in the IOL plane. Compared with its nontoric pseudo-accommodating counterpart, Crystalens (Bausch & Lomb), it had greater reduction in absolute cylinder and better uncorrected visual acuity, with 96.1% of patients having 58 or less of IOL rotation postoperatively [10]. PREOPERATIVE DETERMINATION OF CORRECT MAGNITUDE AND AXIS Identifying the appropriate toric lens to implant requires accurate preoperative measurements to assess the axis and amount of astigmatism. There are various ways to identify these values preoperatively. Manual keratometry, automated keratometry, and simulated keratometry have been shown to have good interdevice agreement for minimum, maximum, and average keratometry, with automated keratometry having better repeatability [11]. These modalities had good interdevice agreement for sphere, astigmatism, and axis, but they also had significant outliers. Placido and Scheimpflug imaging showed good agreement for corneal power and cylinder but not for axis unless the corneal astigmatism was 2 diopters or greater [12 && ]. Studies suggest that combining data from more than one keratometry measurement technique, with at least one measurement from automated technology, reduced the chance of outliers [13 && ]. Manual and automated keratometry devices estimate refractive power of the cornea based on anterior corneal curvature alone. However, the posterior cornea also adds astigmatic value, tends to be against-the-rule, and stays stable over time compared with the anterior cornea, which tends to shift towards against-the-rule over time. It also compensates for astigmatism arising from the anterior corneal surface in younger patients [14]. Not accounting for posterior corneal astigmatism leads to residual astigmatism after toric IOL implantation, overcorrecting by a factor of 1.38 in with-therule eyes and undercorrecting by a factor of 0.65 in against-the-rule eyes [15 &&,16 &&,17]. Surgically induced astigmatism also plays an important role in refractive outcome after toric implantation. Factors associated with surgically induced astigmatism include long limbal incision, high preoperative corneal astigmatism, older age, shallow anterior chamber depth [18] and corneal biomechanical factors [19]. This surgically induced astigmatism affected not just the anterior corneal surface but also the posterior corneal surface [20 & ]. In addition, the effective lens position (ELP) impacts the magnitude of cylindrical correction by a toric lens. Goggins et al. [21] showed that the corneal plane effective cylindrical power of a monofocal toric IOL was influenced by the anterior chamber depth (ACD) and pachymetry. Eom et al Volume 27 Number 1 January 2016

3 Intraocular lens alignment Thulasi et al. Table 1. FDA-approved toric intraocular lenses available in the United States Model A-constant Lens design Overall diameter Optic body diameter Lens surface Material Edge design Monofocal toric intraocular lenses Acrys of IQ Toric IOL 119 Loop haptic 13.0 mm 6.0 mm Biconvex toric aspheric optic Phenylethyl acrylate and phenylethyl methacrylate copolymer Staar Toric TL Plate haptic Biconvex toric aspheric optic Staar Toric TF Plate haptic Biconvex toric aspheric optic Technis Toric IOL (Abbott) Loop haptic 13 6 Biconvex toric aspheric optic Single plate Silicone Single plate Silicone Hydrophobic acrylic Posterior square edge Multifocal toric intraocular lenses Acrys of IQ ReSTOR multifocal toric IOL Loop haptic 13.0 mm 6.0 mm Aspheric, biconvex, apodized Pseudo-accommodating toric intraocular lenses Trulign Toric BL1UT (Bausch and Lomb) Loop haptic 11.5 mm 5.0 mm Aspheric with axis marks on anterior surface, toric on the posterior surface Acrylate/ methacrylate copolymer with UV and blue light filter Silicone with enhanced UV protection Posterior square edge Spherical power Cylindrical power in IOL plane Add power þ6.00 to þ31.0 Din0.5D increments, þ31.0 to þ34.0 in 1.0 D increments þ1.50 to þ6.00 Din 0.75D steps þ9.5 toþ23.5d þ2.0 and þ3.50d þ24.0 to 28.5D þ2.0 and þ3.50d þ5 to þ34.0 D in 0.5 D increments 1.00,1.50, 2.25,3.00, 4.00D þ6.0 to þ34d in half diopter increments 1.00D, 1.50D, 2.25D, 3.00D to 33.0D in 0.50D steps 1.25D, 2.00D, 2.75D Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved. 67

4 Cataract surgery and lens implantation took this a step further to calculate the ELP with the Haigas formula and found that as the ACD and predicted ELP increased, the effectiveness of correcting corneal astigmatism using the manufacturer predicted toric IOL decreased [22]. Similar results were shown by Savini et al. [23] not just with axial length but also with keratometric values, with flatter Ks leading to overcorrection and steeper Ks to undercorrection. These results were not limited to monofocal toric IOLs. Multifocal IOLs also showed similar dependence on keratometric values and effective lens positioning [24]. Pseudo-accommodating lenses such as Crystalens also showed wide variability in postoperative refractive outcomes, with improvement in predictability when effective lens positioning was taken into account [25]. There are multiple manufacturer-provided calculators that use manual or automated keratometry and a surgeon-specific surgically induced astigmatism value to obtain the spherocylindrical power and axis of lens implantation (Fig. 1). Most do not take into account the contribution of the posterior cornea, although the most recent calculator by Barrett does use basic conversions to compensate for the predicted posterior astigmatism. Many of these calculators also use a single conversion factor between IOL plane cylindrical power and the corneal plane cylindrical power for a given sphere equivalent, without taking into account anterior chamber depth and pachymetry value. This can become significant, especially for eyes with axial lengths that are outside of the average values [23]. There are various nomograms in literature that adjust for these variables [16 &&,26]. When various methods of adjusting corneal astigmatism were compared, the Baylor Nomogram outperformed the Alcon and Holladay toric calculators, but the Barrett toric calculator had the best predicted residual astigmatism in patients with toric IOLs [27]. MANUAL TECHNIQUES TO DETERMINE PATIENT ALIGNMENT There are two independent, critical steps for ultimate toric IOL alignment patient alignment to accurately determine the steep meridian intraoperatively, and toric IOL alignment once the steep meridian has been determined. Misalignment of the toric IOL axis causes reduction of the cylinder power along the desired meridian and/or induction of cylinder in a new meridian. If misalignment occurs, the new residual cylinder can be estimated using the formula: R ¼j2Csin Q j where C is the cylinder power of the toric lens and Q is the degree of misalignment. This is a sinusoidal relationship, with each degree of misalignment causing approximately 3% of the lens power to be lost so that at 30 degrees off intended axis, the toric effect is neutral [28,29]. It is therefore crucial to achieve proper alignment of the toric IOL. This is especially important in multifocal toric lenses, where uncorrected distance visual acuity was more affected by rotation than monofocal toric lenses [30]. There are now a variety of automated and manual techniques for patient marking. Cyclotorsion needs to be taken into account while marking a patient, with studies in laser in situ keratomileusis (LASIK) showing more than 28 of cyclotorsion in up to 68% of patients when they change position from sitting to lying flat, with some patients having a much higher amount of cyclotorsion [31]. Hence, when using manual techniques, patients are usually marked preoperatively while fixating on a distance object to minimize any cyclotorsion that may influence lens positioning. There are several manual alignment techniques that can be used to determine the axis of alignment. The three-step technique involves marking the eye at the horizontal meridian at the slit lamp or using various marking devices, intraoperatively using another device with angular gradations, and then marking the limbus or cornea at the desired angle of alignment with a marking pen or needle. The threestep procedure with a bubble marker found a mean error in axis of 2.48, and a total error in toric IOL alignment of 4.98 [32 & ]. When various other methods of marking the eye preoperatively coaxial slit beam turned to the 3-o clock and 9-o clock position, a bubble marker, a pendular marker, or a tonometer marker were compared, both pendular marking and slit-lamp marking had similar rotational deviation to the reference meridian, with the least vertical misalignment observed in the slitlamp marking device [33]. A one-step technique using a slit-lamp eyepiece in which the slit beam is rotated to the meridian of interest has also been described [34]. With the advent of femtosecond laser-assisted cataract surgery, alignment using small intrastromal marks created by the femtosecond laser at the intended toric meridian following manual pen marking as a guide has also been utilized [35]. Multifocal IOLs and accommodating lenses pose different challenges when it comes to alignment. Diffractive lenses especially rely on centration such that the lens is concentric to the visual axis. These lenses also necessitate that the central ray coming through the cornea is perpendicular to the center of 68 Volume 27 Number 1 January 2016

5 Lens recommendation OS (Left) BARRETT TORIC CALCULATOR K INDEX K INDEX VE CYLINDER -VE INDEX Toric IOL Calculator guide Patient data Date: 20/08/2015 Surgeon:XX ID: XX Patient:XX l Surgeon & patient information Surgeon Name Patient Name Additional patient information (I.D., Case, etc.) Lens datails T r l Intraocular lens alignment Thulasi et al. (b) (a) Flat K: 44.64@ 169 Steep K: 46.81@ 79 e m Left Eye A Constant/LF: / 1.99 AL: ACD: 2.92 p o N a s a Induced astigmatism (SIA): Degrees a AcrySof IQ Toric IOL SN6AT5 IOL Spherical equivalent (SE) 25.5 D Axis of placement 73 Cylinder power 3.00 D (IOL plane) Cylinder power 2.06 D (Corneal plane) Calculation datails 225 Pre-op corneal astigmatism: 2.17 D 79 Surgically induced astigmatism: 0.50 D 45 Refraction - (S.E.Q) Toric power IOL power T e m p o 270 IOL: SN6AT5 25.5D SE, 73 Flat 169 Steep 79 P.IOL:25.5D SIA:0.50D IL:135 [V:3.2.2] 60173bf8fb92467bb9f31b5a4335a7f28/19/15 16:18: D 73 Crossed-cylinder result (corneal plane): 0.34 D S.E (Biconvex) T4 Anticipated residual Astigmatism: (c) S.E. T (Biconvex) r a OS 0.26 S.E. T (Biconvex) l Toric power IOL cylinder Residual astigmatism Temporal Cyl axis T3 Recommended IOL: 25.5 D T4 Axis 67 Cylinder power: IOL plane 2.25 dw corneal plane 1.53 D Target refraction sph. / 0.21 cyl axis 67 degrees Cyl axis T Cyl axis T5 Alcon SN6ATx Formula: holladay II Incision: 135 SIA: 0.50D IOL Placement axis: 73 IOL ideal toricity: Res. refraction: D 163 Procedure: Std phaco SRG Entrd ACD(Opt): 5.67 IOL Ref D D D 73 Lens Res. refraction SN6AT2 SN6AT D D D D D 163 SN6AT4 SN6AT5 SN6AT6 SN6AT7 SN6AT8 SN6AT9 FIGURE 1. Toric IOL calculators. (A) The Alcon toric IOL calculator for Alcon IOLs. (B) The Barrett toric calculator. (C) The Holladay IOL consultant toric IOL calculator. Note that these three images arose from the same data entry for the same case; both the recommended toric power and alignment differed for each calculator Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved. 69

6 Cataract surgery and lens implantation Date Name Eye Birth Doctor position Steep axix: 149 Implantation axix: 150 Limbus: φ11.6mm Pupil: φ3.0mm Bottom Main incision: Astigmatism axis: dpt 59 Steep axis: Paracentesis: 45 Absolute Flat axis: Paracentesis: 241 Nasal STEEP Temporal Capsulorhexis: Pre-OP pupil 5.0 Lens model: SNGAT3 Lens power: D Top Centration: Pre-OP pupil Load recent Check calibration Cancel OK FIGURE 2. The Verion Digital Marker (Alcon Labs, Inc.) for planning toric IOL power and alignment preoperatively. the lens. Studies show that in refractive lenses, as the angle kappa of a patient increased, their photic symptoms of glare and halos increased [36,37]. Chang and Waring recommend centering the lens along the subject-fixated coaxially sighted corneal light reflex axis, as represented by Purkinje image 1 on the anterior corneal surface while the patient is fixating [38]. IMAGE-GUIDED TECHNIQUES TO DETERMINE PATIENT ALIGNMENT Another approach to marking the desired meridian is using image-guided systems to provide a reference point intraoperatively. Preoperative anterior segment photos have been used to map the axis with comparable or better rates of meridional error. In this method, the desired meridian is measured from two reference limbal vessels. These vessels are then used to mark the axis intraoperatively [39]. Given the high degree of accuracy of astigmatism correction in excimer laser ablation, similar iris fingerprinting to identify the desired meridian has also been suggested [40]. Integrated image-guided systems such as Verion (Alcon; Fig. 2), Callisto (Carl Zeiss AG, Gena, Germany), which integrates into the OPMI Lumera 700 (Carl Zeiss AG), and True Vision (True Vision Systems, Goleta, CA, USA; Fig. 3) using Cassini Topographer (i-optics, The Hague, The Netherlands) utilize these imaging-guided techniques to allow intraoperative overlay of preoperative imaging so that the axis of astigmatism is visible in the microscope as the toric IOL is placed. Early results using the Cassini/TrueVision system showed a mean error in rotation of and all patients had a corrected distance visual acuity of 20/25 or better [35]. INTRAOPERATIVE ABERROMETRY Despite optimized preoperative measurements and alignment techniques, postoperative astigmatism is still an issue, especially in those with challenging preoperative measurements. Intraoperative aberrometry allows for intraoperative refinement of lens selection and rotation. WaveTec Optiwave Refractive Analysis (ORA; WaveTec Vision Systems Inc., FIGURE 3. The True Vision (True Vision Systems) intraoperative digital overlay to assist with intraoperative toric IOL alignment Volume 27 Number 1 January 2016

7 Intraocular lens alignment Thulasi et al. Aliso Viejo, CA, USA) uses Talbot-Moire interferometry to produce a specific fringe pattern and the aberrations in this fringe pattern are analyzed, and a specific refractive value is generated using a proprietary algorithm. It is performed twice during cataract surgery, with the aphakic readings providing the spherical and cylindrical IOL power and the pseudophakic readings guiding toric IOL placement and titration of limbal relaxing incisions. Another aberrometer is Holos (Clarity Medical Systems, Pleasanton, CA, USA), which provides a continuous readout of residual refractive error throughout surgery [41]. Aberrometry readings can theoretically be affected by lid speculum, surgical corneal edema, and many other intraoperative factors [42], with the most successful and reproducible readings found in aphakia with viscoelastic [32 & ]. Despite these limitations, in a recent study by Hatch et al. [43 && ] the intraoperative aberrometry group was 2.4 times more likely to have 0.50D or less in residual refractive astigmatism compared with standard methods. Wavefront aberrometry in this study changed intraoperative decision making significantly, with the cylinder power being changed 24% of the time, the spherical power changed 25% of the time, and three or fewer rotations needed 92% of the time [43 && ]. Intraoperative aberrometry has also been shown to be superior to conventional methods in patients with prior myopic LASIK or PRK, a group with variable predictability of IOL measurements with conventional toric calculations [44,45 & ]. Other studies have found less impressive results when using intraoperative aberrometry [46 48]. INTRAOPERATIVE TECHNIQUES FOR TORIC IOL ALIGNMENT Despite optimal toric IOL choice and placement on axis, intraoperative techniques can significantly influence the eventual position of the toric IOL and thus the residual astigmatism. Studies have shown that lens rotation occurs as early at 1 h after surgery and usually remains stable until 1 month after surgery [7,30]. The most likely cause of this early rotation is incomplete removal of viscoelastic or movement of lens during viscoelastic removal. Removal of viscoelastic causes rotation of the lens in a clockwise direction. Incomplete removal of viscoelastic, especially from behind the IOL, can also cause rotation of the IOL. It is therefore important to remove all viscoelastic from the eye. Initial manufacturer recommendations were to leave the toric IOL aligned short of the intended axis prior to removal of the viscoelastic and then adjusting the IOL to be aligned with the intended axis, thus preventing the IOL from needing to be rotated 1808 in case of an overshoot. However, the authors Table 2. Reasons for residual astigmatism after toric intraocular lens placement Preoperative Problems Causes Intraoperative Postoperative Errors in measurement Axis determination errors Inaccurate lens selection Material of lens selected Calculator used for lens selection Cyclotorsion Inaccurate marking of axis Surgically induced astigmatism Changes secondary to effective lens positioning Rotation during viscoelastic removal Rotation postoperatively Postoperative topographic changes Irregular surface Interdevice variability Posterior corneal astigmatism Small optic of lens Hydrophilic lenses Plate haptic Silicone Long limbal incision, high-preoperative corneal astigmatism, older age, shallow anterior chamber, corneal biomechanical properties Anterior chamber depth and pachymetry Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved. 71

8 Cataract surgery and lens implantation 23º 180º 0º Rotating the toric IOL 157º clockwise should minimize the astigmatism. 270º Current toric position: 75º Ideal toric position: 98º Residual astigmatism versus axis Magnitude of astigmatism (Diopters) Astigmatism after IOL rotation Baseline astigmatism of eye without toric IOL Axis of IOL (Degrees) FIGURE 4. Image from the Berdahl & Hardten toric IOL calculator ( demonstrating optimal toric IOL alignment to minimize residual astigmatism. In this case, the patient s current residual astigmatism was 3.25D, and rotating the IOL 238 (1578 clockwise) was predicated to result in 0.43D residual astigmatism. As this value was acceptable, IOL rotation was undertaken. have found that to be less successful than properly aligning the IOL from the outset and then fixating it in place during viscoelastic removal, either using the IA hand piece to hold the IOL against the posterior capsule, or by using a second instrument to fixate the IOL. CAUSES OF RESIDUAL REFRACTIVE ASTIGMATISM AFTER TORIC IOL PLACEMENT Despite the use of appropriate toric IOLs, patients may have visually significant residual refractive astigmatism. The most common causes for residual astigmatism are listed in Table 2. Errors in preoperative measurement of cylinder and axis can certainly lead to inaccurate toric intraocular lens implantation. Posterior corneal astigmatism exerted the highest influence on error in refractive astigmatism, more so compared with surgically induced astigmatism, effective lens positioning, and postoperative IOL orientation [49]. IOL design and materials also have a significant role in postoperative astigmatism. A recent study with Lentis Unico L-312T aspheric toric IOL (Oculentis GmbH, Berlin, Germany) found significant rotation of IOL up to 9 months after lens implantation [50]. Despite this lens having an open loop haptic design and a hydrophobic surface, 10.6% of IOLs were rotated 308 or more, highlighting that not all toric IOLs have the same stability in the eye Volume 27 Number 1 January 2016

9 Intraocular lens alignment Thulasi et al. Although some degree of rotation has been noted, repositioning rates of toric IOLs are fairly low, with rates of 1.1% with Acrysof Toric IOL [51] and 3.3% with STAAR AA4203 AL lenses (STAAR Surgical Company, Monrovia, CA, USA) [52]. Another reason for low rates of repositioning is that rotations less than 10 degrees result in less than 0.50D of astigmatism, which may not be clinically significant [53]. Even with appropriate orientation of the toric IOL in the intended axis, postoperative astigmatic surprises may be secondary to other factors such as fluctuating keratometry, posterior corneal curvature, unexpected surgically induced astigmatism, or variance between the axes of astigmatism at different optical zones [54]. REVISION OF MISALIGNED TORIC INTRAOCULAR LENS: REPOSITIONING OR REPLACEMENT Many of the above factors may necessitate the rotation of a toric IOL to a different axis postoperatively. Berdahl and Hardten created a toric results analyzer, which determines the ideal position of the toric IOL [54,55]. It uses the patient s postoperative manifest refraction and power and current axis of the toric IOL to predict the ideal axis of toric IOL and predict a postrotation refraction (Fig. 4). Keeping in mind that astigmatism is a vector, it may not always be possible to rotate the current IOL into a position that will maximize astigmatic correction (Fig. 5). In these cases, an IOL º 45º 180º 0º Rotating the toric IOL 135º clockwise should minimize the astigmatism. 270º Current toric position: 125º Ideal toric position: 170º Magnitude of astigmatism (Diopters) Residual astigmatism versus axis Astigmatism after IOL rotation Baseline astigmatism of eye without toric IOL Axis of IOL (Degrees) FIGURE 5. Image from the Berdahl & Hardten Toric IOL calculator ( demonstrating optimal toric IOL alignment to minimize residual astigmatism. In this case, the patient s current residual astigmatism was 2.25D, and there was no rotation that was predicted to result in less than 1.4D residual astigmatism, so IOL rotation was not undertaken Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved. 73

10 Cataract surgery and lens implantation exchange may be necessary, using a different power toric IOL. Intraoperative techniques used to achieve this rotation are determined by the length of time from initial surgery and degree of adhesion formation between the IOL and the capsular bag. Chang recommends operating within the first few weeks postoperatively, and using the paracentesis incision and BSS on a long cannula to free up any capsular adhesions to the IOL and rotating the toric to the intended axis [51]. When using the astigmatismfix. com website, the appropriate axis will be determined relative to the current axis; therefore, intraoperative marking is only necessary relative to the implanted IOL rather than requiring determination of the 180 axis. This reduces repositioning variability and maximizes outcomes after IOL rotation. Corneal-based refractive procedures such as LASIK and PRK can also be used to correct any residual refractive astigmatism. When LASIK was compared with lens exchange and piggyback IOLs, LASIK outperformed the other two, with greater reduction in spherocylinder refractive error [56]. Jin et al. also showed good reduction in spherical equivalence with LASIK, with 92% of patients within 0.50D of intended correction. However, there was no statistically significant difference in spherical equivalence between the LASIK and lensbased surgery groups [57]. Recently, femtosecond-assisted astigmatic keratotomies after refractive procedures have shown good reduction in astigmatism and spherical equivalence [13 &&,58,59]. Although no studies in patients undergoing femtosecond-assisted astigmatic keratotomies after toric IOL implantation have been reported, this may also be a reasonable option for these patients. CONCLUSION As patients increasingly expect optimal refractive outcomes with minimal astigmatism after cataract surgery, accurate evaluation, placement, and revision of toric IOLs are essential skills for every cataract surgeon. There are multiple steps in the process that are critical for success, including preoperative determination of astigmatism magnitude and axis, intraoperative patient alignment, IOL alignment, and IOL fixation into its long-term positioning. A variety of techniques currently exists to achieve these goals. Future research will be directed to clarify which of the current or future methods are best at each step in the process. Acknowledgements None. Financial support and sponsorship This work is supported in part by an unrestricted departmental grant to Emory University Department of Ophthalmology and Baylor College of Medicine Cullen Eye Institute from Research to Prevent Blindness, Inc. Conflicts of interest There are no conflicts of interest. REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Hoffer KJ. Biometry of 7500 cataractous eyes. Am J Ophthalmol 1980; : Hayashi K, Manabe S, Yoshida M, Hayashi H. Effect of astigmatism on visual acuity in eyes with a diffractive multifocal intraocular lens. J Cataract Refract Surg 2010; 36: && Visser N, Beckers HJ, Bauer NJ, et al. Toric vs aspherical control intraocular lenses in patients with cataract and corneal astigmatism: a randomized clinical trial. JAMA Ophthalmol 2014; 132: Randomized multicenter trial that showed that toric IOLs provided more spectacle independence compared to aspheric controls. 4. Linnola RJ, Werner L, Pandey SK, et al. Adhesion of fibronectin, vitronectin, laminin, and collagen type IV to intraocular lens materials in pseudophakic human autopsy eyes. Part 2: Explanted intraocular lenses. J Cataract Refract Surg 2000; 26: Linnola RJ, Werner L, Pandey SK, et al. Adhesion of fibronectin, vitronectin, laminin, and collagen type IV to intraocular lens materials in pseudophakic human autopsy eyes. Part 1: histological sections. J Cataract Refract Surg 2000; 26: Chang DF. Early rotational stability of the longer Staar toric intraocular lens: fifty consecutive cases. J Cataract Refract Surg 2003; 29: Prinz A, Neumayer T, Buehl W, et al. Rotational stability and posterior capsule opacification of a plate-haptic and an open-loop-haptic intraocular lens. J Cataract Refract Surg 2011; 37: & Perez-Vives C, Ferrer-Blasco T, Garcia-Lazaro S, et al. Optical quality comparison between spherical and aspheric toric intraocular lenses. Eur J Ophthalmol 2014; 24: A comparative wavefront aberration analysis of spheric and aspheric toric IOLs, indicating that aspheric toric IOLs had overall better optical quality compared with spheric lenses. 9. Hayashi K, Masumoto M, Takimoto M. Comparison of visual and refractive outcomes after bilateral implantation of toric intraocular lenses with or without a multifocal component. J Cataract Refract Surg 2015; 41: Pepose JS, Hayashida J, Hovanesian J, et al. Safety and effectiveness of a new toric presbyopia-correcting posterior chamber silicone intraocular lens. J Cataract Refract Surg 2015; 41: Mehravaran S, Asgari S, Bigdeli S, et al. Keratometry with five different techniques: a study of device repeatability and inter-device agreement. Int Ophthalmol 2014; 34: && Delrivo M, Ruisenor Vazquez PR, Galletti JD, et al. Agreement between placido topography and Scheimpflug tomography for corneal astigmatism assessment. J Refract Surg 2014; 30: Observational case series evaluating inter-device agreement between Placido topography and Scheimpflug tomography, showing good agreement between corneal cylinder and power but not axis 13. && Browne AW, Osher RH. Optimizing precision in toric lens selection by combining keratometry techniques. J Refract Surg 2014; 30: This study compared manual keratometry with four automated keratometers. Although all devices had good agreement, there were significant outliers. The authors suggest that errors be reduced by averaging manual keratometry with any automated keratometry. 14. Ho JD, Liou SW, Tsai RJ, Tsai CY. Effects of aging on anterior and posterior corneal astigmatism. Cornea 2010; 29: && Goggin M, Zamora-Alejo K, Esterman A, van Zyl L. Adjustment of anterior corneal astigmatism values to incorporate the likely effect of posterior corneal curvature for toric intraocular lens calculation. J Refract Surg 2015; 31: This study recommended a coefficient of adjustment to calculate a more appropriate IOL cylindrical power for both with-the-rule and against-the-rule astigmatism rather than using anterior corneal curvature alone Volume 27 Number 1 January 2016

11 Intraocular lens alignment Thulasi et al. 16. Koch DD, Jenkins RB, Weikert MP, et al. Correcting astigmatism with toric && intraocular lenses: effect of posterior corneal astigmatism. J Cataract Refract Surg 2013; 39: This study showed that most automated devices overestimated corneal astigmatism in with-the-rule and underestimated astigmatism in against-the-rule astigmatism. The Baylor nomogram is suggested in this paper. 17. Koch DD. The posterior cornea: hiding in plain sight. Ophthalmology 2015; 122: Chang SW, Su TY, Chen YL. Influence of ocular features and incision width on surgically induced astigmatism after cataract surgery. J Refract Surg 2015; 31: Denoyer A, Ricaud X, Van Went C, et al. Influence of corneal biomechanical properties on surgically induced astigmatism in cataract surgery. J Cataract Refract Surg 2013; 39: Nemeth G, Berta A, Szalai E, et al. Analysis of surgically induced astigmatism & on the posterior surface of the cornea. J Refract Surg 2014; 30: This study analyzed the effect of surgically induced astigmatism by measuring preoperative and postoperative Scheimpflug-based keratometry and found a statistically significant role of SIA on the posterior cornea. 21. Stringham J, Pettey J, Olson RJ. Evaluation of variables affecting intraoperative aberrometry. J Cataract Refract Surg 2012; 38: Eom Y, Kang SY, Song JS, et al. Effect of effective lens position on cylinder power of toric intraocular lenses. Can J Ophthalmol 2015; 50: Savini G, Hoffer KJ, Carbonelli M, et al. Influence of axial length and corneal power on the astigmatic power of toric intraocular lenses. J Cataract Refract Surg 2013; 39: Pinero DP, Camps VJ, Ramon ML, et al. Error induced by the estimation of the corneal power and the effective lens position with a rotationally asymmetric refractive multifocal intraocular lens. Int J Ophthalmol 2015; 8: Pinero DP, Camps VJ, Ramon ML, et al. Positional accommodative intraocular lens power error induced by the estimation of the corneal power and the effective lens position. Indian J Ophthalmol 2015; 63: 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; 129: Abulafia A, Barrett GD, Kleinmann G, et al. Prediction of refractive outcomes with toric intraocular lens implantation. J Cataract Refract Surg 2015; 41: Ma JJ, Tseng SS. Simple method for accurate alignment in toric phakic and aphakic intraocular lens implantation. J Cataract Refract Surg 2008; 34: Till JS, Yoder PR Jr, Wilcox TK, Spielman JL. Toric intraocular lens implantation: 100 consecutive cases. J Cataract Refract Surg 2002; 28: Garzon N, Poyales F, de Zarate BO, et al. Evaluation of rotation and visual outcomes after implantation of monofocal and multifocal toric intraocular lenses. J Refract Surg 2015; 31: Ciccio AE, Durrie DS, Stahl JE, Schwendeman F. Ocular cyclotorsion during customized laser ablation. J Refract Surg 2005; 21:S772 S & Huelle JO, Katz T, Druchkiv V, et al. First clinical results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol 2014; 98: First large study examining intraoperative aberrometry in cataract surgery predictable results were obtained in aphakia with viscoelastic, showing that aberrometry is a viable option for intraoperative planning in cataract surgery. 33. Popp N, Hirnschall N, Maedel S, Findl O. Evaluation of 4 corneal astigmatic marking methods. J Cataract Refract Surg 2012; 38: Packer M. Effect of intraoperative aberrometry on the rate of postoperative enhancement: retrospective study. J Cataract Refract Surg 2010; 36: Montes de Oca I, Kim EJ, Wang L, et al. Accuracy of toric intraocular lens alignment and predicted residual astigmatism using a 3D computer-guided visualization system in femtosecond laser-assisted cataract surgery. Invest Ophthalmol Visual Sci 2015; 56: Prakash G, Prakash DR, Agarwal A, et al. Predictive factor and kappa angle analysis for visual satisfactions in patients with multifocal IOL implantation. Eye (Lond) 2011; 25: Karhanova M, Maresova K, Pluhacek F, et al. [The importance of angle kappa for centration of multifocal intraocular lenses]. Cesk Slov Oftalmol 2013; 69: Chang DH, Waring GO. The subject-fixated coaxially sighted corneal light reflex: a clinical marker for centration of refractive treatments and devices. Am J Ophthalmol 2014; 158: Cha D, Kang SY, Kim SH, et al. New axis-marking method for a toric intraocular lens: mapping method. J Refract Surg 2011; 27: Osher RH. Iris fingerprinting: new method for improving accuracy in toric lens orientation. J Cataract Refract Surg 2010; 36: Krueger RR, Shea W, Zhou Y, et al. Intraoperative, real-time aberrometry during refractive cataract surgery with a sequentially shifting wavefront device. J Refract Surg 2013; 29: Stringham J, Pettey J, Olson RJ. Evaluation of variables affecting intraoperative aberrometry. J Cataract Refract Surg 2012; 38: && Hatch KM, Woodcock EC, Talamo JH. Intraocular lens power selection and positioning with and without intraoperative aberrometry. J Refract Surg 2015; 31: This retrospective study showed that adjusting preoperative lens selection with intraoperative aberrometry was more likely to decrease residual refractive astigmatism than standard toric intraocular lens selection 44. Canto AP, Chhadva P, Cabot F, et al. Comparison of IOL power calculation methods and intraoperative wavefront aberrometer in eyes after refractive surgery. J Refract Surg 2013; 29: & Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology 2014; 121: This is a case series of patients undergoing intraoperative aberrometry with theoptiwaverefractiveduringcataract surgery after prior myopic LASIK or PRK. It showed more accurate results than using other traditional preoperative methods. 46. Packer M. Effect of intraoperative aberrometry on the rate of postoperative enhancement: retrospective study. J Cataract Refract Surg 2010; 36: Hemmati HD, Gologorsky D, Fau - Pineda R 2nd, Pineda R 2nd. Intraoperative wavefront aberrometry in cataract surgery. Semin Ophthalmol 2012; 27: Fram NR, Masket S, Wang L. Comparison of intraoperative aberrometry, OCT-based IOL formula, Haigis-L, and masket formulae for IOL power calculation after laser vision correction. Ophthalmology 2015; 122: Savini G, Naeser K. An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses. Invest Ophthalmol Vis Sci 2015; 56: Maedel S, Hirnschall N, Chen YA, Findl O. Rotational performance and corneal astigmatism correction during cataract surgery: aspheric toric intraocular lens versus aspheric nontoric intraocular lens with opposite clear corneal incision. J Cataract Refract Surg 2014; 40: Chang DF. Repositioning technique and rate for toric intraocular lenses. J Cataract Refract Surg 2009; 35: Chang DF. Comparative rotational stability of single-piece open-loop acrylic and plate-haptic silicone toric intraocular lenses. J Cataract Refract Surg 2008; 34: Felipe A, Artigas JM, Diez-Ajenjo A, et al. Residual astigmatism produced by toric intraocular lens rotation. J Cataract Refract Surg 2011; 37: Lockwood JC, Randleman JB. Toric intraocular lens rotation to optimize refractive outcome despite appropriate intraoperative positioning. J Cataract Refract Surg 2015; 41: Berdahl JP, Hardten DR. Residual astigmatism after toric intraocular lens implantation. J Cataract Refract Surg 2012; 38: ; author reply Fernandez-Buenaga R, Alio JL, Perez Ardoy AL, et al. Resolving refractive error after cataract surgery: IOL exchange, piggyback lens, or LASIK. J Refract Surg 2013; 29: Jin GJ, Merkley KH, Crandall AS, Jones YJ. Laser in situ keratomileusis versus lens-based surgery for correcting residual refractive error after cataract surgery. J Cataract Refract Surg 2008; 34: Ruckl T, Dexl AK, Bachernegg A, et al. Femtosecond laser-assisted intrastromal arcuate keratotomy to reduce corneal astigmatism. J Cataract Refract Surg 2013; 39: Venter J, Blumenfeld R, Schallhorn S, Pelouskova M. Nonpenetrating femtosecond laser intrastromal astigmatic keratotomy in patients with mixed astigmatism after previous refractive surgery. J Refract Surg 2013; 29: Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved. 75