EyeWorld India March 2013 Issue

10 March 2013 EWAP FEATURE Views from Asia-Pacific Tim ROBERTS, MBBS, MMed, FRANZCO, FRACS Consultant Ophthalmologist and Clinical Senior Lecturer, Department of Ophthalmology, Royal North Shore Hospital, University of Sydney Consultant Eye Surgeon, Vision Eye Institute Level 3 270 Victoria Ave, Chatswood, Sydney, Australia 2067 Tel. no. +61-2-9424-9999 Fax no. +61-2-9415-4220 tim.roberts@visioneyeinstitute.com.au A fter myopia and hypermetropia, astigmatism remains the major optical aberration causing reduced vision. A significant number of patients presenting for cataract surgery have coexisting astigmatism, which if left uncorrected, is likely to result in reduced postoperative visual quality. 1 Assessing cataract surgery success by only looking at best-corrected visual acuity or spherical equivalent targets will result in suboptimal refractive outcomes and dissatisfied patients. Improvements in cataract surgery and intraocular lenses (IOLs), combined with a generational change in patient expectations, have resulted in a paradigm shift with spectacle independence now regarded by most ophthalmologists and patients as the expected and desired outcome following surgery. Accurately measuring preoperative keratometric cylinder and planning for spherical and astigmatic emmetropia should be the target for all patients when removing cataracts. Various techniques have been used in combination with non-toric IOLs to reduce or eliminate astigmatism; however, these techniques have been limited by induced higher-order aberrations, the amount of astigmatism that can be treated and the long-term mechanical stability of the cornea following relaxing incisions. Options to treat astigmatism include incision placement on the steep corneal meridian, paired opposite clear corneal incisions, corneal relaxing incisions and laser refractive surgery. The availability of toric IOLs based on widely used non-toric IOL platforms, combined with improved rotational stability, has made toric IOLs a viable option for many surgeons. They produce accurate and predictable refractive results and do not require additional expensive instrumentation or special surgical skills and training. The construction of a circular, consistently-sized capsulorhexis which overlaps the IOL throughout 360° is important in maximizing IOL stability and reducing the onset of posterior capsular opacification .2 The recent introduction of femtosecond lasers to cataract surgery has shown promising results with reports of greater precision and accuracy of the anterior capsulotomy and more stable and predictable positioning of the intraocular lens .3,4,5 The FS laser can also create extremely accurate corneal incisions for both the main wound and astigmatic relaxing incisions in the steep corneal meridian. Key factors in achieving successful results with toric IOLs are thorough education of office, anesthetic and nursing staff, proper patient selection, accurate measurement of corneal cylinder, and accurate IOL alignment intraoperatively. The cardinal meridians are marked on the cornea with the patient in the upright position prior to commencing surgery. These reference marks can be made with commercial instruments or by the surgeon aligning the horizontal meridian with the horizon. Correct alignment of the toric IOL axis can be confirmed under the operating microscope by using a fixation ring (Mendez marker, Mastel Inc., Rapid City, SD, USA) after wound hydration and reformation of the anterior chamber. Key Points • After myopia and hypermetropia, astigmatism remains the major optical aberration causing reduced vision • A significant number of patients presenting for cataract surgery have coexisting astigmatism, which if left uncorrected, is likely to result in reduced postoperative visual quality • Best-corrected visual acuity and spherical equivalent refraction should not be used as indicators of good refractive outcomes • Calculations should not be based on the subjective refraction as progressive lenticular astigmatism may either mask corneal astigmatism or give a falsely high estimate of cylinder • Manual and automated keratometry measurements are reliable with comparable results • Topography should be performed if astigmatism >1.5 D to exclude corneal pathology References 1. Ferrer-Blasco T, Montés-Micó R, Peixoto-de-Matos SC, Gonzá-les-Méijome JM, Cerviño A. prevalence of corneal astigmatism before cataract surgery. J Cataract Refract Surg. 2009;35:70-75. 2. Ravalico G, Tognetto D, Palomba M, et al. Capsulorhexis size and posterior capsule opacification. J Cataract Refract Surg. 1996;22:98-103. 3. Kránitz K, Miháltz K, Sándor GL, et al. Intraocular lens tilt and decentration measured By Scheimpflug camera following manual or femtosecond laser-created continuous circular capsulotomy. J Refract Surg. 2012;28:259-63. 4. Roberts TV, Lawless M, Chan CC, et al. Femtosecond laser cataract surgery: technology and clinical practice. Clin Experiment Ophthalmol. 2012 Jul 12. doi: 10.1111/j.1442-9071.2012.02851.x. [Epub ahead of print] 5. Kránitz K, Takacs A, Miháltz K, et al. Femtosecond laser capsulotomy and manual continuous curvilinear capsulorrhexis parameters and their effects on intraocular lens centration. J Refract Surg. 2011;27:558-63.Editors’ note: Dr. Hwang and Prof. Joo have no financial interests related to their comments. Editors’ note: Dr. Roberts has no financial interests related to his comments. intraoperatively so that landmarks are identified, ensuring proper lens positioning. Meanwhile, William B. Trattler, MD , director, Cornea, Center for Excellence in Eye Care, Miami, Fla., USA, emphasized the need for topography on all astigmatic patients. “You need a topography because you can be surprised if the astigmatism is quite irregular,” he said. “It could be keratoconus or it could be other irregularities, and unless you use the topography, you’ll have no idea.” This could lead to trouble in a case in which, for example, the IOLMaster identifies 1 D of astigmatism. If the practitioner assumes that this is regular and implants a toric lens, if it turns out to be irregular that will make things worse, Dr. Trattler warned. He uses the IOLMaster on every patient to help measure the axial length and determine the right intraocular lens power, pairing this with Placido disk topography. In unusual cases he also employs the Pentacam, which measures the shape of the cornea. “They’re very complementary and can be helpful in figuring things out,” Dr. Trattler said. Dr. Holladay stressed that no single device currently serves all functions. “The topography wavefront devices don’t measure the back surface or the thickness of the cornea, and the tomography devices measure the front and the back surface of the cornea but don’t measure the wavefront,” he said. “So you don’t get everything from any one of them.” What is needed, he thinks, is a tomographer that measures wavefront. With no single device available, this may mean reconciling conflicting measurements. In cases of discrepancies, Dr. Trattler recommended averaging measurements or repeating the tests. Dr. Lane advised trusting your own experience. He pointed out that while manual keratotomy remains the gold standard, accuracy somewhat depends on operator experience. However, with Getting - from page 9