Eyeworld

EW FEATURE 48 Rebirth of laser vision correction • June 2017 AT A GLANCE • Patients with irregular corneas are often left with significant visual disabilities and require gas permeable contact lenses or penetrating keratoplasty to improve their quality of vision. • Topography-guided laser ablations, a new technology approved in the U.S. in 2016, are unique in that they combine myopic and hyperopic ablations to create a more regular corneal surface. • Patients with thin corneas that are ectatic should undergo corneal crosslinking, which has recently been approved by the U.S. Food and Drug Administration and has been used in Europe for more than 15 years. • If patients are not candidates for topography-guided PRK or wavefront aberrometry, the cone can be flattened using phototherapeutic keratectomy with the excimer laser. by Michelle Stephenson EyeWorld Contributing Writer 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 exces- sive central steepening and a large myopic shift. Be cautious in patients with good uncorrected acuity as the treatment could decrease uncorrect- ed visual acuity while improving best corrected visual acuity. Patients may not be happy if they need to wear corrective glasses or contact lenses after surgery if they didn't prior to surgery," Dr. Stein said. According to Raymond Stein, MD, director, Bochner Eye Institute, Toronto, and associate professor of ophthalmology, University 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 corrected visual acuity with keratoconus, pellucid marginal degeneration, and ectasia after laser vision correction. "Preferred cases are corneas at least 450 µm thick with a dioptric difference across the Several new technologies are allowing refractive surgeons to significantly improve these patients' quality of vision K eratoconus is the most common cause of irregu- lar corneas. Other causes include ectasia, trauma, scarring, and previous procedures, such as radial keratot- omy. These patients are often left with significant visual disabilities and require gas permeable contact lenses or penetrating keratoplasty to improve their quality of vision. "One of the greatest advances in refractive surgery has been the abil- ity to treat irregular corneas," said Eric Donnenfeld, MD, Rockville Centre, New York. "Now, thanks to the advent of several new technolo- gies, refractive surgeons are able to significantly improve many of these patients' quality of vision. Many times, these patients will no longer Treating irregular corneas need to wear gas permeable lenses, but can wear soft contact lenses or glasses. On occasion, these patients can go spectacle-free." For patients with mild corneal irregularities, Dr. Donnenfeld prefers performing wavefront aberrometry treatment, which treats the entire visual system including the anterior cornea/posterior cornea and lens. "This can be for very mild cases of forme fruste keratoconus and some other corneal irregularities," he explained. New technologies are allowing surgeons to treat more severe irreg- ularities. Topography-guided laser ablations A new technology approved in the U.S. in 2016 is topography-guided laser ablations. This is unique in that it combines myopic and hyperopic ablations to create a more regular corneal surface. "With topographic ablations, we are able to treat more significantly irregular corneas, such as more advanced keratoconus," Dr. Donnenfeld said. "We have found that we can capture images with the Topolyzer [Alcon, Fort Worth, Texas] in patients who have corneas as steep as 60 D. The key aspect of topographic ablations is that they can not only flatten the steep areas of the cornea, but they also steepen the flat areas of the cornea so that we can improve patients by up to 10 D of corneal irregularity on a fairly routine basis." Topography-guided PRK (rather than LASIK) is performed on these patients because they already have thinner corneas. "Mitomycin is used to prevent scarring, and patients are told that visual 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 recent ASCRS•ASOA Symposium & Con- gress] we presented a series of 68 patients who had a mean improve- ment in best corrected visual acuity of two lines and a mean improve- ment in uncorrected visual acuity of four lines," Dr. Donnenfeld said. Figure 1. Topography-guided PRK and corneal crosslinking: preoperative, postoperative, and difference map. The postop map shows significant reduction in the irregular astigmatism; the difference map shows 7.4 D of flattening over the cone and 5.9 D of steepening to the superior cornea; best corrected spectacle acuity improved from 20/80 to 20/25. Figure 2. Topography-guided PRK and corneal crosslinking: preoperative, postoperative, and difference map. Postop map shows normalization of the corneal contour; best corrected spectacle acuity improved from 20/50 to 20/25. Source: Raymond Stein, MD

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