EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/111385
February 2013 Refractive/astigmatism Report from the Pentacam, which can measure the shape of the cornea and astigmatic regularity and magnitude Source: Jack T. Holladay, M.D. are automated like the measurements that you would take with an IOLMaster or with the Lenstar,��� he said. ���Some of them have been around for many decades like manual keratometry, and some of them are looked at in terms of corneal topography or even OCT.��� Intraoperatively, Dr. Lane sees systems such as the ORA and the Holos as serving an important function. ���With the WaveTec aberrometry and in the future with Clarity aberrometry, that will help us to determine what the amount of astigmatism is after we���ve removed the cataract on the table, real-time,��� he said. He also stressed the importance of using a guidance system for proper intraoperative lens placement. ���We have guidance systems because with astigmatism not only is there an amount, there���s also a direction,��� he said. ���So you can choose the correct power implant, but if you put it in the wrong position you���ll be inaccurate in your correction of the astigmatism.��� Guidance devices such as the SMI (Alcon, Fort Worth, Texas) take a photograph of the eye and match this intraoperatively so that landmarks are identified, ensuring proper lens positioning. Meanwhile, William B. Trattler, M.D., director, Cornea, Center for Excellence in Eye Care, Miami, 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 kera- toconus 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 (Oculus, Lynnwood, Washington), 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 continued on page 52