Eyeworld

108 April 2016 EW REFRACTIVE SURGERY by Maxine Lipner EyeWorld Senior Contributing Writer Birth order's effect on myopia F irst-born children have a reputation for lording things over their younger siblings. However, one thing that appears to be stacked against the eldest is a greater like- lihood that he or she will develop myopia, according to Jeremy A. Guggenheim, PhD, Cardiff Univer- sity, Cardiff, U.K. Study results pub- lished in the December 2015 issue of JAMA Ophthalmology indicate that first-born individuals are 10% more likely to develop myopia and 20% more apt to have more severe, high myopia, he reported. Prior to conducting the study, investigators had heard anecdotally that there could be such a rela- tionship, Dr. Guggenheim noted. Results from a prior analysis of 15- to 22-year-olds suggested that for first-born individuals, myopia was 10% more common than for their later-born siblings. "It's not a large amount, only about a 10% increased risk, but it did seem to be cropping up," Dr. Guggenheim said. "We were intrigued as to whether this was a real robust finding or a chance and variation." myopic was lower than for their first-born sibling, he noted. Education's effect One of the theories from the lit- erature was that education could influence the development of my- opia, and this was something that investigators had the chance to explore. "We had the chance to look at whether education was having a potential influence here," Dr. Guggenheim said, adding that the theory is that for the first-born child, parents tend to invest more time and effort into education, which enables such offspring to do slightly better in school. In turn, the more education a person is exposed to, the higher the risk of being shortsighted, Dr. Guggenheim explained. "Near work and educa- tion have been closely linked to shortsightedness for decades," he said. "That seems the most plausible explanation for why we might be finding this link between birth order and myopia." Previous studies have also indicated that time spent outdoors in childhood plays a role in whether or not a person develops myopia, Dr. Guggenheim said. "We were not able to examine the effects of spending time outdoors in our latest study. However, in our earlier research project, taking this factor into account didn't seem to change the relationship between birth order and myopia." He concluded, "The available evidence suggests that insufficient time spent outdoors and having a higher birth order are separate risks." From a clinical perspective, Dr. Guggenheim views the new study as bringing to light another piece of the puzzle showing that education is linked to myopia. This is anoth- er factor to keep in mind when weighing how much education children should receive. "I think as an optometrist and someone who doesn't want to see myopia levels rising inexorably higher, we need to think about children's eyes as well as their education," Dr. Guggenheim said. "Perhaps they do need time outdoors and other activities in their lives." EW Editors' note: Dr. Guggenheim has no financial interests related to this article. Contact information Guggenheim: guggenheimj1@cardiff.ac.uk Eyes on the eldest New cross-sectional study To determine whether this was a birth-order issue or just an anomaly, investigators conducted a cross-sec- tional study of UK Biobank partici- pants recruited from 2006 to 2010. Biobank is a national health resource aimed at improving prevention, diagnosis, and treatment for a wide range of health issues. "We looked at around 90,000 people with ages from 40 to 69," Dr. Guggenheim said, adding that these people were invited to take part in a U.K.-wide health study and weren't recruited because of any eye conditions. "That was one of the nice things," he said. "Sometimes population groups we have access to have some special interest in eye conditions, but that may bias the sample." Investigators found this study's results were in line with the much smaller prior one. "We found the same sort of risk—about a 10–20% increased risk of being myopic if you're the first born child," Dr. Guggenheim said. Then the risk goes down depending on the number of older brothers or sisters a person has. Investigators determined that, for example, in those who were the sixth born, the chance of being and adverse effects such as suture-re- lated complications and infections. "However, with the advent of femtosecond lasers, the accuracy and predictability of the tissue addition techniques has improved significantly, thus improving patient outcomes," she explained. Low risk of rejection Although the procedure described by Dr. Ganesh and his team almost certainly amounts to corneal trans- plantation, which could carry a risk of rejection, the risk is low. "Unlike traditional full thick- ness grafts, which have a graft-host junction proximal to host limbus, in this technique, the lenticule was well protected in the host corneal pocket and did not come in direct contact with the host's limbal vascu- lature and immune system, making the risk of allogeneic graft rejection remotely possible," they explained. In addition, because the lent- icule was mainly stromal collagen tissue, they emphasized that the probability of rejection is significant- ly low compared with endothelial rejection. Should rejection occur, the reversibility of the procedure poses an advantage. "Nevertheless, there is a need to monitor for signs of rejection and treat it like allogeneic graft rejec- tion should rejection occur," they reported. "Because it is a reversible proce- dure, the lenticule can always be ex- planted in the event of any adverse effects or rejection in the future," Dr. Ganesh said. Based on initial results involv- ing FILI in hyperopia, the technique may be more beneficial compared to hyperopic LASIK in the treatment of moderate hyperopia in terms of stability, regression, aberrations, and postoperative dry eye. "Although it is a bit early to predict the refractive outcomes, initial data indicate that the cryo- preservation technique used is safe in heterologous individuals," Dr. Ganesh said. While preliminary results are promising, more studies are needed to fully assess the potential of FILI as an alternative in the treatment of hyperopia. "Further studies with a larger co- hort and modification of the surgical technique with a goal of reducing postoperative astigmatism and refining nomograms are suggested to determine the long-term safety and refractive effects on the cornea and establish the technique as a valid op- tion to treat hyperopia," Dr. Ganesh and team concluded. Other novel applications of SMILE-extracted lenticules For treatment of keratoconus in mild to moderate cases, Dr. Brar and colleagues 2 modified the surgical technique. Instead of implanting the whole lenticule, they punched the central 3 mm with a corneal trephine, thus creating a dough- nut- shaped lenticule. This tissue was then implanted into a pocket created at a 100-micron depth into the cornea with a femtosecond laser. This was followed by injection of 0.25% riboflavin dye with an appli- cation time of 1 minute followed by ultraviolet radiation exposure for 3.3 minutes, thus delivering total energy of 6.3 J to the cornea. In their expe- rience treating 9 eyes with mild to moderate keratoconus, with a mean follow-up of 12 months, Dr. Brar and colleagues observed a significant improvement in UCVA and BCVA with reduction in mean keratom- etry, asphericity, and total higher order aberrations. Biomechanical changes studied with the Corvis ST (Oculus, Wetzlar, Germany) showed improvement in stiffness of the cornea postoperatively, suggesting that tissue addition in combination with accelerated crosslinking may be Novel continued from page 106

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