Eyeworld

EW FEATURE 86 Laser vision correction • February 2018 Considerations continued from page 84 AT A GLANCE • Topography-guided laser ablation is starting to gain popularity in the United States. • It has evolved from a treatment for damaged corneas to a treatment for keratoconus and a tool for enhancing laser refractive surgery outcomes. • Some think topography-guided laser ablations will increase in popularity as more surgeons realize that it doesn't take much longer to plan topographic ablations and that the results are better. by Michelle Stephenson EyeWorld Contributing Writer Current considerations for optimizing topographic ablations measured astigmatism from topog- raphy to determine the modified refraction, which is then used for laser entry. Surgeons must make their own determination based on what the topography says and what the refraction says as to what they want to come up with the final product of astigmatism axis and magnitude that they treat. When it comes to axis, I try to stay as close to the topographic axis as I can, and in about 75% of my cases, I'm on that axis. But because there is posterior astigmatism and internal astigmatism, I will use other tools to help determine whether I should be treating closer to the manifest refraction axis than the topographic axis because of those differences. Sometimes I will treat between the topography axis and the manifest After gaining popularity globally, topographic ablations are gaining traction in the U.S. T opography-guided laser ablation has gained popu- larity internationally and is starting to gain popularity in the United States. It has slowly evolved from a treatment for damaged corneas to a treat- ment for keratoconus and a tool for enhancing laser refractive surgery outcomes. "Since the initial clinical trial when everyone was excited about the results of topographic treat- ments, surgeons have realized that topographic ablations are not as easy as they seem," said Michael Gordon, MD, San Diego. "They may not be getting the expected results, or it may take too much time to plan. I think the adoption of topographic ablations has suffered because of this. There are so many variants now that people are con- fused about what procedure to use on which patients." Ronald Krueger, MD, Cleve- land, has been using topographic ablations since their FDA approval several years ago. "Over the course of time what I have learned about optimizing these ablations is that I will try to treat as close to the topographic axis of astigmatism as I can," he said. "However, where the topographic axis deviates from the refractive axis, I will use addi- tional tools to choose the proper axis of astigmatism that I should be treating. One needs to compare the manifest refraction with the To document progression or understand the high risk for it, Dr. Ambrósio urged characterizing the susceptibility for biomechanical failure of the cornea using advanced corneal imaging, including Placido front surface topography and tomog- raphy with Scheimpflug and OCT. "The latter, OCT, along with very high frequency ultrasound, provides the ability for layered or segmental tomography, providing critical data related to epithelial thickness, for example," Dr. Ambró- sio said. Biomechanical data also has been useful for making clinical deci- sions, mainly in borderline cases. "In a routine exam, we should always pay attention to the patient's complaints," Dr. Ambrósio said. "If the patient notices worsening vision, that fact is a major alert." Post-refractive patients Post-PRK, post-LASIK, and post- SMILE corneas that develop post- operative corneal ectasia should undergo CXL upon diagnosis, Dr. Randleman said. "The treatment is most effective at halting progression, so if per- formed early enough the resulting vision loss can be reduced," Dr. Randleman said. However, as a prophylactic pro- cedure, this is still controversial, and recent data has found that CXL does not completely prevent ectasia after LASIK, 2 Dr. Ambrósio said. Dr. Hardten checks the topog- raphy of post-corneal refractive surgery patients at risk for ectasia annually if they are older and every 6 months in young patients. Along with routine exams, Dr. Ambrósio asks about the quality of vision and performs wavefront analysis. For progression documen- tation, he advocates for subtraction maps from the axial curvature, and also from the front and back elevation maps using the respective 8.0-mm best fit spheres for the first measurement. Post-CXL treatment Another ongoing debate is the best surgical timing for patients who need CXL and also desire laser vi- sion correction. "There are valid arguments for simultaneous treatment with exci- mer laser ablation followed imme- diately by corneal crosslinking and literature to support the efficacy of this approach," Dr. Randleman said. "Others, including myself, advocate sequential treatment, with crosslink- ing first followed by excimer laser ablation only when the patient has stabilized and only if laser treatment would be highly beneficial given the inherent risks and uncertainties that come with ablating an ectatic cornea." He urges patients to wait a minimum of 6 months and prefera- bly 12 months after CXL to consider laser treatment. Dr. Ambrósio underscored the need to understand the patient's sit- uation, including symptoms, wishes, and demands, as well as efforts to obtain balance between the eyes. He advocates for performing the thera- peutic custom surface ablation and CXL in the same day as reported by A. John Kanellopoulos, MD, in the Athens protocol. 3 Dr. Ambrósio uses a fast CXL protocol with 18 mW/ cm 2 for 5 minutes. When performing therapeutic laser vision correction on eyes also undergoing CXL, Dr. Ambrósio said that the indication is key. "Less ablation is usually more efficient," Dr. Ambrósio said. "Cus- tomization with topo-guided using either Scheimpflug or Placido is possible, but in some cases, just the PTK is indicated." As crosslinking can have contin- ued long-term flattening effects over many years, Dr. Randleman noted that it is important not to be too aggressive with any laser ablation. "If the surgeon targets em- metropia and the patient continues to flatten over time there will be induced hyperopia," Dr. Randleman said. EW References 1. Ambrósio R Jr. Therapeutic refractive sur- gery: Why we should differentiate? Rev Bras Oftalmol. 2013;72:85–6. 2. Taneri S, et al. Corneal ectasia after LASIK combined with prophylactic corneal cross-linking. J Refract Surg. 2017;33:50–52. 3. Kanellopoulos AJ. Comparison of sequen- tial vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg. 2009;25:S812–8. Editors' note: Dr. Ambrósio has finan- cial interests with Oculus, Alcon (Fort Worth, Texas), Carl Zeiss Meditec (Jena, Germany), and Mediphacos (Belo Horizonte, Brazil). Dr. Hardten has financial interests with Johnson & Johnson (Santa Ana, California) and Avedro (Waltham, Massachusetts). Dr. Randleman has no related financial interests related to his comments. Contact information Ambrósio: dr.renatoambrosio@gmail.com Hardten: drhardten@mneye.com Randleman: randlema@usc.edu continued on page 88

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