EyeWorld Asia-Pacific September 2017 Issue

Wavefront-guided vs. wavefront-optimized laser treatments by Michelle Stephenson EyeWorld Contributing Writer The wavefront measurement principle with a Tscherning device, in which wavefront deviation data is derived from projected patterns on the retina, imaged, and analyzed Source: A. John Kanellopoulos, MD continued on page 52 EWAP REFRACTIVE 51 September 2017 Both provide good outcomes with minimal induction of higher-order aberrations W avefront-guided and wavefront-optimized laser treatments offer advantages over tradi- tional laser treatments. In the past, many patients had night vision complaints after traditional LASIK. These complaints are rare with the more advanced algorithms. “Wavefront-guided and wave- front-optimized are two different algorithms for trying to provide the best quality vision to patients desiring laser vision correction with LASIK and PRK,” said William Trat- tler, MD , Miami. Michael Greenwood, MD , Fargo, North Dakota, agreed. “Wavefront- guided and wavefront-optimized are great treatment options in many patients. Wavefront-guided will reduce preexisting higher-order aberrations, while wavefront-opti- mized will minimize the induction of new higher order aberrations. Both are superior to conventional treatments, which are more likely to induce higher order aberrations fol- lowing refractive surgery,” he said. Wave front-guided According to Dr. Trattler, wavefront- guided treatments use measure- ments of each patient’s unique optical pathway to design a treat- ment that will correct the patient’s refractive error, including any mild irregularities in the optical path- way. “It’s taking an individualized scan of each eye, and the software develops a customized treatment based on the patient’s unique find- ings,” he explained. It’s an excellent treatment for patients who have a clear lens and preexisting higher-order aberra- tions, Dr. Greenwood said. “How- ever, it might not be the best option for someone who is in his or her 50s and has some lens changes; the wavefront is picking up aberrations that are from the lens rather than from the cornea. You would be treating the higher-order aberra- tions in the lens,” he said. According to Michael Gordon, MD , San Diego, “The thought behind wavefront-guided treatments is that if we can measure wavefront aber- rations with a reliable wavefront sensor and we have a scanning spot laser that has a tracker, we would be able to correct wavefront errors and make quality of vision better. That’s where wavefront came about. How- ever, unless you get above 0.4 μm of RMS higher order aberrations, you don’t see better results than with wavefront-optimized.” The problem with wavefront- guided treatments is that they are dynamic. “In other words, they change with pupil diameter, they change with accommodation, and they change with age. I think most people in the United States, other than those using a VISX platform [Johnson & Johnson Vision, Santa Ana, California], do not use wavefront-guided. Surgeons using a WaveLight laser [Alcon, Fort Worth, Texas] typically do not use wavefront-guided treatments as the initial treatment, particularly now that we’ve got topography-guided,” Dr. Gordon said. Wavefront-optimized According to Dr. Gordon, wave- front-optimized treatment, his- torically, was developed because surgeons realized that when energy was delivered to the periphery of the cornea, particularly with the scanning spot laser, some energy was lost. “One reason for this is the cosine effect: Because we’re coming tangential to the cornea, a certain percentage of the energy is reflected and not absorbed. Second, because the round beam is on a curved surface, coming again tangential, it becomes ovalized. The energy characteristics change, meaning the energy density changes because now it’s a bigger spot size but the same energy. Now we’re delivering less energy to any given spot. Because of those two characteris- tics, we weren’t getting as much en- ergy as we needed delivered to the peripheral cornea, which basically generated more spherical aberration than one wanted. People with big pupils, in particular, would have night glare issues. Wavefront opti- mization was a way to deliver more energy to the peripheral cornea to compensate for the loss in a scan- ning spot laser,” he explained. Dr. Trattler noted that wave- front-optimized treatments were developed after evaluating postop- erative LASIK results and making adjustments in the algorithm for treating and reshaping the eye to improve the quality of vision by improving the transition zone of the treatment, which is the area between the optical zone and the rest of the cornea. “One of the arguments regard- ing use of wavefront-optimized over