FEB 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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Page 48 of 114

46 These factors do not have an effect on LASIK outcomes, according to a new study T emperature and humidity were previously thought to be a factor in LASIK out- comes, but a new study by Michael Seider, MD, and Steven Schallhorn, MD, San Diego, looked at this and discovered that there is no impact. Dr. Schallhorn discussed the study and results and why he believes this to be a defini- tive conclusion. This work was part of a large study, which took place in the United Kingdom and Ireland and analyzed LASIK outcomes in a large number of patients. The study looked at more than 200,000 eyes treated between January 2008 and June 2011. The purpose of the study was to determine if temperature and hu- midity differentials in the OR had an impact on LASIK outcomes. Factors like patient age, gender, flap creation technique, pre- and one-month post-LASIK manifest refraction, and ambient temperature and humidity during LASIK were all recorded. The study determined that there was in fact no impact and that tem- perature and humidity do not play a role in LASIK outcomes because there was no clinically significant evidence found. The conclusion stated Òneither procedure room tem- perature nor humidity during LASIK were found to have a clinically significant relationship with postoperative manifest refraction in our population.Ó Dr. Schallhorn explained that the study was an effort by Optical Express, of which he is the global medical director. ÒWe want to con- tinually improve outcomes,Ó he said. ÒThis is part of that effort.Ó ÒIf temperature and humidity are important for outcomes, we would use that information to drive better outcomes,Ó Dr. Schallhorn said. One issue with previous studies on this topic was that they did not include as many patients in the sample size; therefore it may have been difficult to derive a meaningful conclusion. ÒIn all previous studies, the sample sizes were very small in relative comparison,Ó he said. Furthermore, Dr. Schallhorn said that the impact of temperature and humidity in the OR was a wide- spread belief, but it was mostly anec- dotal evidence rather than carefully conducted studies that formed these conclusions. Most people heard that this could be a problem and accepted it, he said, and many believed that this conclusion made sense. ÒIf there is an outlier in a patientÕs refractive outcome, we want to find a reason for it,Ó Dr. Schallhorn said. ÒWhat seemed to be a good reason was the temperature or the humidity in the operating room was off.Ó It is easy to blame the problem on something like this, and it is easy to argue that varying temperature and humidity cause a variance in outcomes. But you have to consider that there were previ- ously no large clinical trials that established this notion, he said. Dr. Schallhorn said he does not believe there will be any future stud- ies similar to this one because of the strong results. ÒThe results are com- pelling,Ó he said. ÒThe sample size is enormous.Ó Although he said he would wel- come anyone who wanted to follow up with this work, the sample size used in the study, combined with the lack of evidence that tempera- ture and humidity play a role, is compelling enough for him. ÒWeÕve looked at such a large sample size, it represents the population that seeks laser vision correction,Ó he said. A much smaller sample size could con- ceivably show a difference simply due to chance. Dr. Schallhorn noted that there are a few caveats to the study. It was designed to test within the range that patients were treated. For exam- ple, if the humidity was around 100% or if the temperature was more than 100 degrees, that could prove problematic, but he said the normal range in which patients were treated is similar for most areas. In that range, he can confidently say that temperature and humidity do not make a difference in the out- comes. If a surgeon lifted the flap and then waited 20 minutes before doing the excimer laser procedure, then perhaps it would matter, but for the most part, the procedure is very standard, he said. ÒTemperature and humidity in the surgical suite do not influence the outcomes,Ó Dr. Schallhorn said. Time of year, time of day, seasonal- ity, location of the clinic, and other factors were all analyzed also. EW Editors' note: Dr. Schallhorn has financial interests with Optical Express and Abbott Medical Optics (Santa Ana, Calif.). Contact information Schallhorn: scschallhorn@yahoo.com EW REFRACTIVE SURGERY 4 6 February 2014 by Ellen Stodola EyeWorld Staff Writer Temperature and humidity in LASIK outcomes Figure 1 displays the effect of operating room humidity (relative humidity percentage) on the postoperative manifest spherical equivalent (diopters). The linear regression line has a slope of zero, indicating no association between the two. F igure 2 displays the effect of operating room temperature (Celsius) on the postoperative manifest spherical equivalent (diopters). The linear regression line has a slope of zero, indicating no association between the two. Source (all): Steven Schallhorn, MD Keep up on the latest in ophthalmology! Follow EyeWorld on Twitter at twitter.com/EWNews EyeWorld @EWNews 46-49 Refractive_EW February 2014-DL2_Layout 1 1/30/14 10:26 AM Page 46

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