EyeWorld Asia-Pacific September 2017 Issue

14 EWAP FEATURE September 2017 procedure can benefit patients of all ages, not just young ones with progressive disease. Older patients with stable corneas have the potential to discontinue rigid gas permeable lenses and return to soft contacts or glasses. A. John Kanellopoulos, MD , clinical professor of oph- thalmology, New York Univer- sity Medical School, and medical director, Laservision.gr Institute, Athens, Greece, said patients who have decentered ablations and irregular ablations resulting from refractive procedures with older laser technologies who complain of ghosting, halos, and difficul- ties with visual function are good candidates for treatment with topography-guided PRK. This procedure will enlarge optical zones and recenter optical zones on the cornea vertex, which is closer to the visual axis of the patient. “Topography-guided PRK does a great job of treating these patients. The pearl here is that topography-guided PRK addresses only the irregularity of the cornea in regard to the vertex, which we assume is the line of sight, and it may hide some refractive surprises postoperatively. Usually, enlarging optical zones or recentering optical zones will result in myopic shift as these treatments with topography resemble hyperopic treatments,” Dr. Kanellopoulos said. Most of these issues can be preempted with a technique called topography neutralization, which may require two steps: (1) to op- timize the cornea as a lenticular system and (2) to address potential myopic shift and more rarely a slight hyperopic shift, in a second, mainly spherical ablation. According to Dr. Stein, the amount of improvement in best corrected visual acuity after topog- raphy-guided PRK is dependent on the preoperative level of best corrected spectacle visual acuity. The greater the preoperative loss of acuity, the higher the potential for lines gained. “In general, the improvement is one to six lines of gain,” he explained. There is a learning curve with this procedure. “Fortunately, this procedure has been performed outside the U.S. since 2003, and our group in particular has worked on topography-guided treatments extensively, with more than 50 peer-reviewed publications and hundreds of presentations in meet- ings over the past 15 years,” Dr. Kanellopoulos said. “Our experi- ence, along with that from other investigators around the world, can serve as a great introduction for clinicians getting involved with topography-guided treatments.” In combination with crosslinking Patients with thin corneas that are ectatic should undergo corneal crosslinking, which has recently been approved by the U.S. Food and Drug Administration (FDA) and has been used in Europe for more than 15 years. “Some surgeons perform crosslinking at the same time as the refractive procedure. I prefer to do them as separate procedures, sepa- rated by approximately 3 months or more,” Dr. Donnenfeld said. “The reason for this is that there is improved epithelial healing and a more stable refractive error once the crosslinking has been stabilized.” Dr. Stein prefers performing corneal crosslinking immediately after topography-guided PRK. “It is important to strengthen a cornea, especially if one removes tissue. Results are more predictable if the corneal crosslinking is done after and not before topography-guided PRK,” he said. Dr. Kanellopoulos found in a landmark study that the combina- tion of topography-guided partial PRK and crosslinking appears to have a synergistic effect in the amount of corneal flattening and normalization. 1 It also results in less scarring. “Additionally, there is the fact that if a cornea has been crosslinked and a surface ablation is attempted after that, the abla- tion will remove the most biome- chanically stable part of the stroma that has been reinforced with the crosslinking process. This may be counterintuitive in the long-term stability of those eyes, so we have since shifted our clinical and surgi- cal paradigm into combining two procedures in what has been known as the Athens protocol. This tech- nique has been adopted by hun- dreds of surgeons internationally, and recently in the United States. It entails the customized topogra- phy-guided or wavefront-guided normalization of the very irregular cornea combined with corneal crosslinking,” he explained. Dr. Kanellopoulos said that the improvement in vision is dramatic, but the postoperative recovery can be lengthier than with standard PRK. “Sometimes, 2 weeks may be required for the cornea to re-epithe- lialize and the surface to normalize. Most of these eyes achieve at least 20/40 best corrected visual acuity, rehabilitation may take several months. They are also told that their vision will be improved, but that they will not be getting rid of their glasses. However, these patients have had significant improvements, and [at the re- CENT¬!3#23s!3/!¬3YMPOSIUM¬ ¬ Congress] we presented a series of 68 patients who had a mean im- provement in best corrected visual acuity of two lines and a mean improvement in uncorrected visual acuity of four lines,” Dr. Donnen- feld said. According to Raymond Stein, MD , director, Bochner Eye Institute, Toronto, and associate professor of ophthalmology, Uni- versity of Toronto, who has been performing topography-guided PRK for the past 8 years, the best candidates for the procedure are those with 20/30 or worse best cor- rected visual acuity with keratoco- nus, pellucid marginal degenera- tion, and ectasia after laser vision correction. “Preferred cases are corneas at least 450 μm thick with a dioptric difference across the cornea of less than 10 D. I would not advise topography-guided PRK if the area of prominent steepen- ing is outside of the pupillary zone because this would result in excessive central steepening and a large myopic shift. Be cautious in patients with good uncorrected acuity as the treatment could decrease uncorrected visual acuity while improving best corrected visual acuity. Patients may not be happy if they need to wear cor- rective glasses or contact lenses after surgery if they didn’t prior to surgery,” Dr. Stein said. Dr. Stein noted that this Treating – from page 13