The goal in modern cataract surgery is emmetropia.With today's technology, emmetropia is easilyachievable for patients with myopic or hyperopicrefractive errors when the appropriate sphericallens power is chosen. In addition to spherical refractiveerrors, astigmatism should be addressed at the time ofcataract surgery so that the patient can achieve the bestpostoperative visual outcomes.
The reduction or elimination of preexisting corneal astigmatismduring or after cataract surgery can be achievedwith several surgical strategies, including excimer laserrefractive procedures such as PRK and LASIK; limbal relaxingincisions; and opposite clear corneal incisions. However, therefractive changes induced by these procedures are relativelyunpredictable, and complications may occur.
Toric IOLs now provide a safe and predictable alternativeto reduce or eliminate refractive astigmatism with a cylindricalcorrection, offering patients with preexisting cornealastigmatism optimal distance visual acuity without the useof spectacles or contact lenses. Approximately 22% ofpatients undergoing cataract surgery have substantialcorneal astigmatism (ie, more than 1.25 D) and would benefitfrom toric IOL implantation.1
ROTATIONAL STABILITY
Two components of toric IOL implantation crucial to thesafety and efficacy of the procedure are accurate surgicalplacement and subsequent rotational stability. As little as10° of axis misalignment reduces the efficacy of astigmaticcorrection by 33%; when the misalignment increases tomore than 30°, it actually induces astigmatism.2
Older toric IOL models were made of silicone, such as theSTAAR Toric IOL (STAAR Surgical Company, Monrovia,California) and the MicroSil Toric IOL (HumanOptics AG,Erlangen, Germany).2,3 Newer toric IOLs are usually made with acrylic materials, which form adhesions with the capsule,leading to rotational stability in the capsular bag withinapproximately 2 weeks.4
TORIC IOL TYPES
AcrySof. The AcrySof IQ Toric (Alcon Laboratories, Inc.Fort Worth, Texas; Figure 1) is currently the most commonlyused toric IOL. This one-piece foldable lens is available inspherical powers ranging from 6.00 D to 30.00 D and cylinderpowers up to 6.00 D. We performed a pilot study in 53 eyesof 43 patients who underwent cataract extraction andAcrySof Toric IOL implantation. Four months postoperatively,refractive astigmatism was less than 0.75 D in 74% of eyes andless than 1.00 D in 91%.5 Almost 80% of eyes achieved a distanceUCVA of 20/25 or better. No complications occurred,and the mean absolute lens misalignment was 3.5 ±1.9°.
A large randomized, controlled trial6 showed similar meanmisalignment at 6 months (3.4° ±3.0°), with a maximum misalignmentof 14° in 250 patients who received the AcrySof IQToric. In the control group, 250 patients were implanted witha nontoric lens (model SA60AT). Two eyes (0.8%) in the toricgroup required surgical intervention to realign the IOL.
Several other noncomparative studies have examinedoutcomes following AcrySof IQ Toric IOL implantation.Results show UCVA of 20/25 in approximately 70% of eyesand refractive astigmatism of 1.00 D or less in more than90%. The mean postoperative IOL misalignment in thesestudies was less than 4°, and surgical repositioning due to IOL rotation was required in 0% to 1.8% of implantedeyes.7-10 Overall, these results indicate that AcrySof IQ ToricIOL implantation is a safe, efficient, and predictablemethod of managing corneal astigmatism in cataractpatients.
Weinand et al11 studied the rotational stability of AcrySofIOLs using digital photographs obtained immediately postoperativelyand 6 months after surgery. The mean IOL rotationwas 0.9° (range, 0.1°–1.8°). These results indicate thatIOL misalignment is largely due to causes other than rotation,including errors during pre- and intraoperative referencemarkings, errors related to IOL positioning during surgery,and postoperative axis readings. Based on currentmarking techniques, we believe a mean misalignment of lessthan 4° is close to optimal.
AT.Comfort/AT.LISA. Previously known as theAcri.Comfort and the multifocal Acri.LISA Toric (CarlZeiss Meditec, Jena, Germany), these lenses are bothone-piece foldable IOLs with optic diameters of 6 mm.The custom-made AT.Comfort and AT.LISA are availablein sphere powers ranging from 0.00 to 32.00 Dand cylinder powers up to 12.00 D. We began usingthe multifocal toric AT.LISA in 2008 (Figure 2) andhave implanted it in 22 eyes of 12 patients (mean age,57.2 ±12.3 years). Mean preoperative keratometryvalue as measured with the IOLMaster (Carl ZeissMeditec) was 3.10 ±1.20 D. After mean follow-up of1.5 ±0.7 months, the postoperative Snellen UCVA andBCVA were 0.9 ±0.2 and 1.0 ±0.2, respectively.Binocular near UCVA at 40 cm, measured with theEarly Treatment Diabetic Retinopathy Study (ETDRS)chart, was 0.1 ±0.1 logMAR. Mean absolute misalignmentwas 2.5 ±2.4°, and surgical realignment wasrequired in one eye. Initial experience indicates excellentvisual outcomes and good stability of the AT.LISAToric IOL (personal communication, N. Bauer).
In a recent study, 10 eyes of six patients with ametropiaand high corneal astigmatism were implanted with the AT.LISA Toric during refractive lens exchange.12 Preoperativerefractive astigmatism ranged from -1.75 to -5.75 D. After 1year, the Snellen distance UCVA was 0.8 or better in six eyesand 1.0 or better in five. Mean reduction in refractive astigmatismwas more than 90%. The mean IOL misalignmentwas 1° to 2°.
Rayner Toric. Other toric IOLs currently available inEurope include the T-flex (Figure 3) and the multifocal MflexT(Rayner Intraocular Lenses Ltd., East Sussex, UnitedKingdom). Rayner toric IOLs are custom-made and availablein cylinder powers ranging from 1.00 to 11.00 D forthe T-flex and up to 6.00 D for the M-flexT. Spherical powersare available up to 34.50 D. Initial clinical experienceswith the Rayner toric IOL, were promising.13-15 No studyresults with this toric IOL have been published so far, andthe current authors have no personal experience withthese lenses.
CONCLUSION
Implanting toric IOLs appears to be an efficient, safe, andpredictable method for managing corneal astigmatism incataract patients and a viable product offering for the premiumIOL surgeon. Those considering introducing toricIOLs to their practice are encouraged to do so, as theselenses provide the opportunity for patients with astigmatismto achieve excellent distance UCVA and resulting spectacleindependence.
Noël J.C. Bauer, MD, PhD, practices in the Department ofOphthalmology at the Academic Hospital, Maastricht,Netherlands. Dr. Bauer states that he is a consultant toAcri.Tec (now Carl Zeiss Meditec). He may be reached ate-mail: n.bauer@mumc.nl.
Nienke Visser, MD, is a doctoral (PhD) student in theDepartment of Ophthalmology at the Academic Hospital,Maastricht, Netherlands. Dr. Visser states that she has nofinancial interest in the products or companies mentioned. Shemay be reached at tel: +31 43 3877133; e-mail: nienke.visser@mumc.nl.
