Contrast Sensitivity after Wavefront Guided LASIK for Myopia

Abstract

Purpose : It is known that refractive surgery for myopia yields reliably predictable outcomes for sphere and cylindrical refractive errors. With wavefront guided LASIK (Laser Assisted in situ Keratomileusis), it is of interest to evaluate contrast sensitivity of subjects before and after surgery. One hypothesis for any contrast sensitivity improvement is the effect of spectacle magnification i.e. minification preoperatively for larger refractive errors that would not be present postoperatively and the aim of the current study was test this hypothesis.

Methods : This was a prospective, non-randomized, clinical study conducted at 12 investigative sites in the USA that included 334 eyes of 170 subjects treated with wavefront-guided myopic LASIK with the iDesign Advanced WaveScan Studio System and Star S4 IR^® Excimer Laser System. Treatment plans derived based on iDesign^® System spherical equivalent (IDSE) refractive error ranged from -1.04 D to -11.98 D. Uncorrected visual acuity (UCVA), contrast sensitivity and refractive outcomes were assessed at 6-months. Monocular, best corrected contrast sensitivity was tested using sine-wave grating charts (spatial frequencies of 3, 6, 12, and 18 cycles per degree [cpd]) at 2.5 meters (8 feet) under three lighting conditions: photopic (85 cd/m²) without glare, mesopic (3 cd/m²) without glare and mesopic with glare.

Results : At 6 months, 98.2% of eyes had UCVA of 20/40 or better, UCVA of 20/20 or better was 82.6%, manifest refraction spherical equivalent within 0.50 D was 68.9% and within 1.00 D was 93.4%. Statistically significant improvements of approximately 0.15 log units or more in mean contrast sensitivity under mesopic conditions with and without glare was seen. Most eyes (≥89%) experienced either no change or an improvement in contrast sensitivity postoperatively; under mesopic conditions with or without glare, there was a four-fold increase in the proportions of eyes with clinically significant (i.e. 0.30 log units at 2 or more spatial frequencies) increases (41%-47%) compared to decreases (≤11%). Contrast sensitivity improvement versus preoperative refractive error showed no relationship for 12 cpd (r = -0.063; p = 0.25) or 18 cpd ( r = -0.065; p = 0.24).

Conclusions : Wavefront guided LASIK for myopia led to improved contrast sensitivity postoperatively. Spectacle magnification does not lead to this improvement in contrast sensitivity.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.