Humidity has modest effect on best-corrected visual acuity

Chicago-Procedure room humidity appears to have a small effect on best-corrected visual acuity (BCVA) outcomes after corneal laser refractive surgery, but variations in humidity or temperature do not appear to affect uncorrected visual acuity (UCVA) outcomes, the incidence of diffuse lamellar keratitis (DLK) after LASIK, or need for enhancement after myopic LASIK or LASEK, according to the results of a retrospective chart review.

The study included data from 873 eyes of 463 patients who underwent femtosecond laser-assisted LASIK or LASEK at the university-based practice between May 2007 and December 2010. Mean follow-up after surgery was about 4 months with a range between 1 and 12 months.

Mean temperature and humidity in the procedure room were 68.4° F and 28.7%, respectively, both falling within manufacturers' recommendations. However, there was a large range for both temperature (58° to 75° F) and humidity (10% to 72%) with some values being outside the recommended environmental conditions.

Linear regression analyses were performed to identify possible correlations between either room temperature or humidity and postoperative UCVA, postoperative BCVA, refractive error, incidence of DLK, and need for enhancement. The only significant association found was between room humidity and BCVA such that increased room humidity was associated with a mild decrease in BCVA. With analyses performed using BCVA data from postoperative visits at 1 day, 1 week, and 1, 3, 6, and 12 months, a significant association was found at most visits. Overall, an 8% rise in humidity in the procedure room translated into a 1 line loss of BCVA.

Unique study

"There have been mixed results from previously published studies investigating the effects of humidity and temperature on laser corneal surgery outcomes, but to our knowledge, none of those studies included eyes having all-laser LASIK," Dr. Mian said. "Femtosecond lasers also have temperature and humidity requirements for proper functioning. To our knowledge, this is the first study of its type including eyes that underwent flap creation with a femtosecond laser with a large sample size as compared to previous reports."

The patients in the study had a mean age of about 39 years, and men and women were equally represented. Mean preoperative values for sphere, cylinder, and spherical equivalent for the group were –3.47, –0.55, and –3.75 D, respectively.

LASIK accounted for about three-fourths of the procedures in the study group. Postoperatively, 76 (11.1%) of the LASIK patients developed DLK and 21 (2.4%) needed an enhancement, while one (0.5%) of the LASEK patients needed an enhancement.

Dr. Mian noted the rates are consistent with previously reported results.

Refractive outcomes were stable during follow-up and functional outcomes were excellent. On the first day postoperative mean UCVA was 20/27 and mean BCVA was 20/22. At 1 year, both improved with mean UCVA reaching 20/18 and mean BCVA being 20/15.

FYI

Shahzad I. Mian, MDE-mail: smian@med.umich.edu

Dr. Mian has no financial interest in the material he discussed.