Influence of spectacle-related changes in retinal image size on contrast sensitivity function after laser in situ keratomileusis.

Purpose: To evaluate changes in contrast sensitivity after laser in situ keratomileusis (LASIK) for the correction of myopia using a monitor-based method and considering the preoperative minification effect of high-diopter spectacles.

Setting: Department of Ophthalmology, University of Vienna Medical School, Vienna, Austria.

Methods: Fifteen eyes of 11 patients had LASIK to correct myopia. The best corrected visual acuity (BCVA) and contrast sensitivity function (CSF) were measured preoperatively and 1, 3, and 6 months postoperatively using the AcuityMax (Science 2020) computer program. The error in contrast sensitivity measurement due to different angular sizes of the test figures deriving from the spectacle refractions before and after LASIK were considered.

Results: Preoperatively, and at 1, 3, and 6 months, the mean Snellen BCVA was 0.93 +/- 0.19 (SD), 0.80 +/- 0.26, 0.85 +/- 0.21, and 0.84 +/- 0.27, respectively. The best mean CS (measured at 1.1 logMAR) was 1.17 +/- 0.05, 1.12 +/- 0.07, 1.13 +/- 0.08, and 1.18 +/- 0.04, respectively. The strongest CS changes were observed at 0.7 logMAR (6 cycles per degree), where CS was 1.10 +/- 0.07 preoperatively and 1.06 +/- 0.09, 1.07 +/- 0.12, and 1.14 +/- 0.07, at 1 month, 3 months, and 6 months, respectively. With correction for the spectacle effect, the preoperative CS was approximately 3% higher and CS at 3 months for intermediate optotype sizes was significantly inferior to preoperatively.

Conclusions: With correction of different retinal image sizes before and after LASIK (due to different spectacle refraction), the CS was significantly below the preoperative values at 1 and 3 months and approached the preoperative values at 6 months. The proposed method is potentially capable of quality monitoring and method comparisons after photorefractive surgery.