Myopic anisometropia

  Early experience indicates that small incision lenticule extraction (SMILE) performed with a proprietary femtosecond laser (VisuMax®, Zeiss) is a promising technique for correcting myopic anisometropia in children in order to facilitate treatment of amblyopia, according to Osama Ibrahim MD. Dr Ibrahim said he has performed 32 cases of SMILE to treat myopic anisometropia in children who were intolerant of glasses or contact lenses. He presented outcomes from follow-up to six months from data collected in 18 eyes that are part of a prospective, non-comparative, interventional case series. Dr Ibrahim reported good predictability and stability for the refractive outcomes. SMILE resulted in improvement in visual acuity, with some eyes even achieving full best spectacle-corrected visual acuity (BSCVA) correction, and no eye lost any lines of BSCVA compared with baseline. POPULARITY “SMILE has demonstrated efficacy and safety for myopic correction in adults, but it has not gained popularity for use in children,” said Dr Ibrahim, Professor of Ophthalmology, Alexandria University, Alexandria, Egypt. “Now we look forward to collecting more data from a larger series of paediatric eyes with longer follow-up, and also to the future availability of SMILE to correct hyperopia.” Dr Ibrahim noted that the history of performing keratorefractive surgery in children to minimise amblyopia caused by anisometropia began with radial keratotomy (RK) and subsequently included the use of photorefractive keratectomy (PRK) and LASIK. “Compared with PRK, LASIK could treat higher refractive error, offered better refractive stability, and had less risk of causing haze and scarring. We have accumulated our own large series of LASIK for myopic anisometropia in children, showing that it improves uncorrected visual acuity and best corrected visual acuity,” he said. He noted that SMILE, however, has advantages relative to LASIK. In addition to being less invasive, causing less dry eye, and offering better biomechanics, SMILE avoids concerns about flap dislocation from eye rubbing or trauma, which is particularly important in children. There is also less potential for risks when operating on an uncooperative child when performing SMILE, and so the procedure can be done with just sedation rather than general anaesthesia. The patients in the series Dr Ibrahim presented ranged in age from six to 12 years. SMILE was performed using local or general anaesthesia and was followed by patching of the dominant eye for a half-day. MEAN BSCVA Preoperatively, mean cycloplegic sphere was -8.78D (range -6.50 to -14.00D), mean cycloplegic cylinder was -1.26D (range up to -3.00D), and mean BSCVA was 0.32 (range 0.05 to 0.4). At six months after SMILE, mean cycloplegic sphere was -1.28D (range +0.75 to -2.25D) and residual cycloplegic cylinder averaged -0.83D (range up to -1.75D). Analysis of spherical equivalent outcomes showed a single eye was overcorrected, while 89% were within 0.5D of the attempted target. “Our refractive outcomes are very good considering this is a population with high myopia. Some cases were left undercorrected, either intentionally because of the refraction in the other eye or because of the correction limit of our nomogram,” Dr Ibrahim explained. REFRACTIONS MEASURED The aim of refractive surgery for myopic anisometropia is not to reach emmetropia or eliminate the need for glasses. Rather it is to allow the child who is spectacle or contact lens intolerant to wear proper correction and do occlusion therapy, he explained. Refractions measured on the day after surgery and at six months were almost the same. “Stability was a main concern because we have seen regression over time in children who underwent RK, PRK, or LASIK for treatment of myopia,” Dr Ibrahim said. BSCVA at last follow-up averaged 0.74 with a range from 0.5 to 1.0. It was unchanged in 61% of eyes, while 16% gained one line, 16% gained two lines, and 5% gained more than two lines. All eyes demonstrated topographic stability during the available follow-up, and review of the topography images showed the area of flattening was larger than the diameter of the lenticule. “This feature helps with visual quality and improvement in BSCVA,” Dr Ibrahim said. Osama Ibrahim: ibrosama@gmail.com