Operating room temperature found to be key driver in LASIK outcomes

Boston-Results of retrospective analyses refute an association between relative humidity in the operating room (OR) and LASIK refractive outcomes.

However, the analyses provide further evidence that room temperature may be a relevant factor, said Robert K. Maloney, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

In a second analysis, he considered the potential influence of OR temperature on primary procedure outcome and compared the ratios of enhancements performed for overcorrection versus undercorrection in groups of eyes that had their primary procedure performed under different temperature conditions.

In a group of 95 eyes later enhanced for a spherical equivalent refractive error >0.5 D from emmetropia after a primary surgery performed when the room was kept at 75° F, eyes being re-treated for overcorrection versus undercorrection were represented 11:1, 87 versus eight eyes. The outcome was reversed in a second cohort of 29 eyes that had enhancement because of spherical equivalent refractive error after a primary procedure performed in an OR set at 70° F. For this population, there was an approximately 9:1 over-representation of eyes being re-treated for undercorrection versus overcorrection, 26 versus three eyes.

"There have been conflicting reports on the effect of OR humidity on LASIK outcomes, but in 2004, Walter and Stevenson [J Cataract Refract Surg. 2004;30:796-803] reported a strong correlation between LASIK enhancement rates and procedure room relative humidity that provided an impetus for many refractive surgeons to install humidity control systems in the laser suite," Dr. Maloney said. "The researchers also found significant correlations between enhancement rates and outdoor relative humidity, outdoor temperature, and procedure room temperature.

"My data show OR humidity had no effect on LASIK outcome, but the finding of a strong impact of temperature may explain the humidity effect reported by Walter and Stevenson," he said. "Perhaps temperature affects LASIK outcomes by influencing laser calibration or performance. Regardless, I recommend keep[ing] the OR at 70° F or less."

Results of a study published in 1994 showing the excimer laser tissue ablation rate increases with corneal dehydration provide plausibility for an association between OR relative humidity and LASIK outcomes.

"Presumably, the effect of [ultraviolet] light on the tissue is altered depending on the amount of water present," he said. "Therefore, it's logical to assume that low room humidity could lead to overcorrection by causing corneal dehydration during surgery, while undercorrection could occur if room humidity is very high."