Effect of environmental factors on myopic LASIK enhancement rates

PURPOSE: To determine whether environmental factors affect laser in situ keratomileusis (LASIK) enhancement rates. SETTING: Wake Forest University Eye Center, Winston-Salem, North Carolina, USA. METHODS: This retrospective chart review comprised 368 consecutive eyes of 191 myopic patients who had LASIK by the same surgeon (K.A.W.). All patients had surgery in 2000 with the Visx Star S2 excimer laser. Refractive outcome, visual acuity, and enhancement rates were monitored closely for 1 year. Fifty-seven eyes (15.5%) had an enhancement procedure. Using enhancement procedure or percentage of correction as the outcome measure, factors that were suspected to affect LASIK results and the need for enhancement were examined; specifically, age, eye, sex, pachymetry, corneal curvature (K), preoperative spherical equivalent, ablation depth, and environmental factors (procedure room temperature, procedure room relative humidity, outdoor temperature, and outdoor relative humidity). RESULTS: Using univariate and multivariate analysis, LASIK enhancement rates strongly correlated with the following variables: procedure room humidity (P =.003; odds ratio OR = 1.093; 95% confidence intervals CI, 1.030-1.160), 2-week preoperative mean outdoor humidity (P =.011; OR = 1.054; 95% CI, 1.012-1.096), outdoor temperature (P =.0059; OR = 1.039; 95% CI, 1.011-1.068), and age (P =.0497; OR = 1.034; 95% CI, 1.001-1.070). The percentage of correction strongly correlated with the following variables: procedure room humidity (P =.021), 2-week preoperative mean outdoor humidity (P =.001), outdoor temperature (P =.0052), and room temperature (P =.017). CONCLUSIONS: The 2-week-preoperative mean outdoor relative humidity, procedure room relative humidity, outdoor temperature, and procedure room temperature may have to be considered during LASIK planning. The effect of these environmental variables on LASIK outcomes warrants further evaluation.