Risk of visual symptoms postLASIK is not predicted by large preoperative pupil size

August 1, 2009

A prospective study including 51 patients who underwent bilateral wavefront-guided LASIK for low to moderate myopia assessed visual symptoms at follow-up visits through 12 months after surgery. There was no evidence that large preoperative pupil size correlated with increased risk of unwanted postLASIK symptoms.

Key Points

"The relationship between pupil size and quality of vision after LASIK is a source of controversy because various publications report different results," said Annie Chan, MD, resident, Department of Ophthalmology, Stanford University, Stanford, CA. "Some investigators have found a correlation, while others advocate not even measuring pupil size preoperatively. Our study was undertaken to address this issue further."

The study was conducted in collaboration with Edward E. Manche, MD, director, cornea and refractive surgery, and professor of ophthalmology, Stanford University School of Medicine. It included 51 patients who underwent bilateral surgery for low to moderate myopia.

The surveys were completed preoperatively and again at 1 week and 1, 3, 6, and 12 months after surgery. They used a rating scale of 0 to 10 where 0 represented no problems and 10 represented the worst response.

To identify the effect of pupil size on outcomes, patients were stratified into three groups based on their mesopic pupil size: small (<5.5 mm), medium (5.5 to 6 mm), and large (>6 mm). Mesopic pupil size and preoperative and postoperative variables were evaluated using analysis of variance.

"We chose these pupil size categories to emulate the analyses performed in the 2003 [study] by Schallhorn and colleagues on pupil size and quality of vision after LASIK," Dr. Chan said.

The patients had an average age of almost 40 years, 63% were females, and 69% were white. They were fairly evenly distributed among the three pupil size groups, and no patient had a mesopic pupil size larger than 9 mm.

The only statistically significant finding appeared in analysis of data for the 12-month visit, when patients with small pupils experienced significantly more glare at night than their counterparts with medium or large pupils. In all groups, glare at night had worsened at 1 month after surgery compared with baseline and then improved with time. By 3 months, patients with medium-size pupils already had less night glare than preoperatively. At the last visit, glare symptoms also were better than at baseline in eyes with large pupils. The condition remained worse than preoperatively in the patients with small pupils, however, and the difference compared with the other groups of pupil size was statistically significant.

"Based on the findings in our study, it is likely that factors other than pupil size play a significant role in quality-of-vision outcomes," Dr. Chan concluded.