EyeWorld India December 2014 Issue

35 EWAP REFRACTIVE December 2014 by Maxine Lipner EyeWorld Senior Contributing Writer Slowing down the myopia train Strategies for decelerating progressive nearsightedness I n some parts of the world myopia has become the norm, with a 90% prevalence level in various Asian populations, according to Thomas A. Aller, OD , senior project scientist, Vision Cooperative Research Center, Sydney, Australia. In the February issue of Eye , Dr. Aller offered strategies for slowing down progressive myopia. On the slow track One tactic to try to halt myopia involves topical use of atropine. The Cochrane Collaboration, from Johns Hopkins, reviewed studies considering this approach, Dr. Aller reported. “Based on the studies that they looked at, their primary recommendation was that atropine had the most promise for controlling myopia,” he said, adding that this has generally been given at a 1% dosage, which has many side effects. “Pupils dilate dramatically, there’s no accommodation, there’s photophobia, and children have to wear bifocals,” Dr. Aller said. “It’s practically a gruesome way to treat myopia.” Still, with the technique, myopia progression was cut to almost zero, he said. However, use of lower doses, potentially with fewer side effects, is also possible. “They found that even 0.01% atropine has a very nice clinical effect approaching 60%,” Dr. Aller said. In addition, with low dosages, the myopia rebound effect experienced when atropine use stopped is not nearly as great. “When you discontinue (traditional) atropine, all of those receptor sites may be hypersensitive, and you get a rebound where the nearsightedness jumps up and you lose a lot of the advantage that you had when you were on it,” he said. “With the 0.01% or the 0.02%, that doesn’t seem to happen.” Orthokeratology (Ortho-K) was another strategy highlighted by the group. “This is the treatment of wearing hard or rigid gas- permeable lenses in order to reshape the eye,” Dr. Aller said. As a result, the center is made flatter and the mid-periphery steeper, akin to laser surgery, he explained. “Ortho-K has been shown to reduce the rate of progression of myopia by 50% in at least one randomized controlled clinical trial, which went on for 3 years,” Dr. Aller said. There is some suggestion, however, that this seems to work better on those with moderate to high levels of initial myopia, he said. With Ortho K, the signal for the eye to stop growing is generated by the power difference between the flattened central cornea and the steepened mid- peripheral area, he said. This might also work with laser treatment; however, it is only FDA approved for non-progressing myopes. “There have been studies to show that 10 years after laser there doesn’t need to be a very high percentage of retreatments,” he said. While this seems to suggest that laser treatment is helpful in forestalling myopia, the eligible patient population is, of course, those who are not progressing, he said. Use of bifocal contacts is yet another approach being tried. “Bifocal contact lenses generally have the distance vision corrected in the center surrounded by either a ring or several rings of plus power,” Dr. Aller said. “In that sense, there’s some similarity between the optical effect of Ortho-K, which has the central distance vision corrected through reshaping with plus in the periphery because it’s uncorrected out there.” A number of studies have put the success rate for use of bifocal contact lenses at about 50%. Dr. Aller has been studying use of bifocal contact lenses in those with a tendency for their eyes to over-converge while reading, known as eso fixation. “That has been shown in a number of studies to be another trigger to myopia progression,” Dr. Aller said. He prescribes bifocal lenses in a way that eliminates the eso fixation disparity, thereby also doing away with one of the triggers to growth. Additionally, these lenses have added plus power in the periphery, something that has been found to slow down nearsightedness. Peripheral stop signal He cited the work Earl L. Smith, OD, PhD , Houston, Texas, U.S., conducted on monkeys. “He showed that by manipulating the focus on the back of the eye in these monkeys you could either cause their eyes to grow or to stop growing,” Dr. Aller said. This flies in the face of the long-held belief that it was the fovea that was important here. “Everyone ignores the periphery, but what he found was that you could manipulate the focus just in the periphery and moderate the growth of the eye without any impact on the central focus,” he said. Ironically, the type of defocus that stimulates myopia progression is what typically results from traditional glasses and contact lenses, he went on. “The holy grail is that typical eyeglass lenses or contact lenses only focus well on the fovea but tend to allow the focus to fall behind the back of the eye,” Dr. Aller said. “That’s a stimulus to growth.” So with classic lenses there’s an out-of-focus image in the periphery because the light is falling behind the retina, he explained. Ideally this could be aligned to the retina, improving peripheral vision and sending a stop signal to myopic growth. However, even an equal amount of blur that fell in front of the retina would not serve as a myopic trigger. Even without availability of such an optimized lens, traditional bifocal contacts can continued on page 41