EyeWorld Asia-Pacific March 2012 Issue

March 2012 20 EW FEATURE Aligning toric IOLs by Michelle Dalton EyeWorld Contributing Editor The iTrace can help surgeons plan their astigmatic corrections Source: William B. Trattler, MD The SMI shows surgeons the location of the axis Source: SensoMotoric Instruments AT A GLANCE • A majority of cataract patients also have astigmatism • The debate on how to measure and treat pre- existing astigmatism is ongoing • Digital marking and intraoperative real-time imaging are helping surgeons be more accurate in toric IOL placement New technologies are helping surgeons overcome some of the obstacles related to placing toric IOLs and maintaining stability W hen it comes to astigmatism, two statistics are bandied about fairly often— astigmatism greater than 0.5 to 0.75 D is likely to affect functional vision, and for every 10 degrees a toric IOL is off its intended correction a patient loses 33% of the lens’s proposed corrective abilities. Until surgeons have an accurate method to align toric lenses, the full benefit of the technology will not be realized, said Robert H. Osher, MD , professor of ophthalmology, College of Medicine, University of Cincinnati, Ohio, USA, and medical director emeritus, Cincinnati Eye Institute, Ohio, USA. “Once we can accurately align, you can be 100% sure that’ll become the standard of care,” he said. Others believe astigmatic correction “is becoming a vital component of cataract surgery”, Haike GUO, MD Professor, Department of Ophthalmology, Guangdong Eye Institute, Guangdong General Hospital, 106 Zhongshan Er Road, Guangzhou, PR China Tel. no. +86-20-83844380 Fax no. +86-20-83844380 guohaike@medmail.com.cn T he debate on how to measure and treat pre-existing astigmatism is ongoing. Around 15 to 20% of cataract patients have at least 1.5 diopters (D) of corneal or refractive astigmatism. In contrast to normal methods for the correction of astigmatism during cataract surgery, such as limbal relaxing incisions in which many variables are involved in the outcome and are not precise enough, toric IOL implantation offers a predictable, stable and safer way to reduce pre- existing astigmatism. Combined with small incisions, cataract surgery techniques can provide a greater opportunity to correct cylindrical errors intraoperatively. For higher amounts of astigmatism, a combination of a toric IOL and astigmatic keratotomy may be the best means to address total amount of cylinder. Accurate determination of the amount of astigmatism is paramount. Corneal astigmatism is usually measured with keratometry or topography. Cylinder and axis are confirmed on manual keratometry (Ks). Ks on an optical biometer such as IOLMaster auto-Ks, slit scanning Ks, Scheimpflug camera Ks, and topographic sim-Ks. But of all the methods we’ve tried, manual keratometry seems to give the most accurate and consistent results. Prior to beginning the surgical procedure, some surgeons prefer to use a pen to mark the axis pre-op and use it as a reference during surgery. Others prefer to use digital markers. Whichever you choose, make sure the patient is upright and looking forward. It is important that the patient be sitting for this procedure as cyclotorsion may occur when the patient lies down. A key point for toric IOLs is the IOL alignment on-axis. IOL rotation can have significant impact on astigmatism correction. Generally, for every 1º of IOL rotation, 3.3% of lens cylinder power is lost. A complete loss of cylinder power can occur with a rotation of >30º. Digital marking and intraoperative real-time imaging are helping surgeons be more accurate in toric IOL placement. Newer diagnostic tools depend on iris landmarks such as the Micron Imaging Systems, the Osher Alignment Toric System, SensoMotoric Instruments and so on. Some diagnostic tools use a reticle and real-time imaging, such as the TrueVision 3D System, in which an overlay template gives the “exact location for the lens”. The WaveTec ORA has the ability to measure corneal astigmatism intraoperatively. New technologies are helping surgeons overcome some of the obstacles related to placing toric IOLs. Today pseudophakic toric IOLs appear to be effective, safe, predictable and efficient tools for managing pre-existing astigmatism during cataract surgery. The newer diagnostic tools bring a high level of precision and accuracy to toric IOL placement, providing flexibility in surgical planning for precise correction of astigmatism. Editors’ note: Prof. Guo is a consultant for Alcon, but has no financial interests related to his comments. Views from Asia-Pacific said Robert J. Weinstock, MD , Weinstock Laser Eye Center, Largo, Fla., USA. But getting a good capture of the astigmatism can be problematic if dry eye is present, said William B. Trattler, MD , director of cornea, Center for Excellence in Eye Care, Miami, Fla., USA. In his general cataract population, more than 60% “have very rapid tear break-up times”, he said, adding he relies solely on corneal curvature data when planning his astigmatic corrections. Lens- or cornea-based? Some surgeons correct astigmatism on the cornea through relaxing incisions. Stephen S. Lane, MD , adjunct clinical professor, University of Minnesota, Minneapolis, Minn., USA, prefers