EyeWorld Asia-Pacific June 2014 Issue

14 June 2014 EWAP FEAturE “You do measurement with three or four devices and it’s astonishing the amount of variability that occurs.” The second issue is the posterior cornea, which introduces an element of astigmatism that can be 0.5 D or more. “We are struggling to get devices that accurately predict it on a patient- by-patient basis,” he said. Once that occurs, Dr. Koch thinks, there will be a distinct, incremental improvement in outcomes with the femtosecond lasers. Dr. Holladay pointed out that tilt and decentration can be factors because the human eye is not along the optical axis. The fovea, which has the finest vision, is not at the posterior pole, it’s five degrees temporal, allowing people to avoid having to look through all the wires of the optic nerve. As a result we also end up with a lens that’s tilted about five degrees. “Both that decentration and tilt result in about 0.5 D of against- the-rule astigmatism,” Dr. Holladay said, adding that this also includes the against-the-rule astigmatism from the posterior cornea. “That has always been there, but we’ve never gotten down to where we’ve been worried about 0.5 diopter of cylinder,” he said. “It’s now getting down to the level where we’re beginning to realize that if we want to get it perfect, we’ve got to compensate for those, too.” Effective lens position Can the precision of femtosecond technology translate into better results? Whether or not IOLs can be better positioned as a result is the key consideration here, Dr. Donnenfeld said. He views the effective lens position as a missing link to achieving optimal results with cataract surgery. “Knowing where the lens is going to sit after cataract surgery is the key to achieving good refractive results,” he said. He added that with biometry now so good, the advantage of the arc of the femtosecond capsulotomy is that it makes the same size capsulotomy every time. As a result, the thinking is that the lens is less likely to vault forward because the capsulotomy is too large or that the lens will be trapped and pulled backward. “There have been several studies showing this improves effective lens position and one study I know of showing it did not,” Dr. Donnenfeld said. “In my estimation, I don’t think there’s any way the femtosecond laser can degrade effective lens position— it can only help.” He thinks he is getting tighter results with femtosecond laser capsulotomies. However, he stressed, studies need to be done on where such capsulotomies need to be placed for best outcomes. “We’re still worrying about where the best place to put these capsulotomies is,” Dr. Donnenfeld said. Dr. Holladay pointed to a study he presented at the 2013 European Society of Cataract & Refractive Surgeons Congress that examined if the location and diameter of the capsulorhexis that are made absolutely consistent because of the precision of the laser shows up in prediction error. He reported that for + or –0.25 D of prediction error with the LenSx laser (Alcon, Fort Worth, Texas, U.S.), that was about 20% better than the Optiwave Refractive Analysis, which was 10% better than standard cataract surgery at one month. Dr. Koch thinks the jury is still out on whether the femtosecond laser helps with effective lens position. “I think the next step where femtosecond lasers will be more beneficial will be when we have lens implants that are designed to take advantage of that very predictable size and location and [we can] attach lenses in a different way,” Dr. Koch said. “I think then we will see a benefit from the effective lens position.” Dr. Alpins concurs. “It would be nice to be able to say that it’s more predictable and more accurate because then you’re going to get better outcomes,” he said. “But in the hands of experienced surgeons that hasn’t been shown to be the case.” He stressed that the accuracy refractively is no better than that attained by an excellent cataract surgeon. “[For a] less than excellent cataract surgeon, femtosecond technology may significantly help by giving consistency to their surgery that their own manual techniques are not giving them,” Dr. Alpins said. Additional tools Pairing the femtosecond laser with other tools can also potentially help to boost outcomes. Dr. Donnenfeld noted that the Verion (Alcon) allows surgeons to account for cyclorotation of the eye at the time of surgery that could improve outcomes. “That allows you to take preoperative pictures of the eye and then overlay them at the time of surgery,” he said. However, he thinks using the Optiwave Refractive Analysis in conjunction with surgery is the best way to get a true reading of the actual cylinder. “The advantage of the Optiwave Refractive Analysis is that not only does it measure the anterior cylinder, it also measures the posterior corneal cylinder as well,” Dr. Donnenfeld said, adding that getting such a true reading allows the practitioner to adjust cylinder very precisely. He finds this helps for toric IOLs as well, pointing out that the Optiwave Refractive Analysis tells the practitioner where to rotate the axis and whether or not to open an incision at the time of surgery to achieve an optimal result. “I think that intraoperative readings are the only way we’re going to always achieve the next level of accuracy with cylinder control because the variables of the visual axis, posterior corneal astigmatism, and the cylinder induced by the cataract incision are all considered with intraoperative aberrometry,” Dr. Donnenfeld said. Overall, Dr. Donnenfeld views astigmatism management as the number one limiting step for most ophthalmologists in achieving optimal refractive outcomes— which he thinks the femtosecond can help to overcome. “With new technology and new interest I believe that we can improve outcomes in a significant way to achieve emmetropia in patients undergoing cataract surgery,” he concluded. EWAP Editors’ note: Drs. Alpins and Stamatelatos have financial interests with the Assort.com web calculators and the Assort.com surgical management systems. Dr. Stamatelatos also has financial interests with ASSORT Surgical Management Systems (Victoria, Australia). Dr. Donnenfeld has financial interests with Abbott Medical Optics, Alcon, Bausch + Lomb (Rochester, NY, U.S.), and WaveTec. Dr. Holladay has financial interests with AcuFocus (Irvine, Calif., U.S.), Alcon, Abbott Medical Optics, Oculus, Visiometrics (Terrassa, Spain), WaveTec, and Carl Zeiss Meditec (Jena, Germany). Dr. Koch has financial interests with Alcon and Abbott Medical Optics. Contact information Alpins: alpins@newvisionclinics.com.au Donnenfeld: ericdonnenfeld@gmail.com Holladay: holladay@docholladay.com Koch: dkoch@bcm.tmc.edu Stamatelatos: george@newvisionclinics.com.au Operating - from page 12