Night vision disturbances after successful LASIK surgery

Abstract

Objective: To evaluate the changes in correlations of higher order aberrations of the first corneal surface with halo phenomena, a form of image degradation, under night vision conditions measured objectively after successful LASIK (laser in situ keratomileusis) surgery. Methods: A prospective, observational, analytical study of 110 eyes that had undergone successful LASIK surgery for myopia and astigmatism. Preoperative sphere was (mean (SD)) 23.48 (1.70) D (0 to 28.00 D) and preoperative cylinder was 20.86 (0.87) D (0 to 24.00 D). Visual disturbance caused by halo phenomena was measured with the Starlights v1.0, and pupil size was measured with Colvard pupilometry after adaptation to a dark environment (0.17 lux). Corneal aberrations were computed for a corneal diameter representative of the eye's entrance pupil under night vision conditions. Results: The halo disturbance index increased in this study by a factor of 2.15 after successful LASIK surgery. Total root mean square for monochromatic higher order aberration displayed a significant correlation with halo disturbance index (r = 0.42; p,0.01). However, only secondary astigmatism (r = 0.36; p,0.01), coma (r = 0.25; p = 0.02) and spherical aberration (r = 0.40; p,0.01) were responsible for such behaviour, with the remaining corneal aberrations up to the sixth order not displaying any significant correlation when considered individually. Conclusion: Patients undergoing LASIK procedures display an increase of halo phenomena around lights in night vision conditions, even when the results of the surgery are considered entirely satisfactory according to current international standards of predictability, efficacy and safety. Secondary astigmatism, coma and spherical aberration are the higher order aberrations up to the sixth order that significantly correlated with halo disturbance index.

Retinal straylight and light distortion phenomena in normal and post-LASIK eyes

“…Despite this, the information provided by the instrument is of great clinical value in trying to explain the visual complaints following corneal surgery. Increase in outcome values after surgery was statistically significant for light distortion, agreeing with previous results [6,19], but not for retinal straylight measurement. At first glance, it could be thought that any reason beyond the occurrence of "haze" could justify an increase in this parameter, but this has been outlined as exclusion criteria.…”

“…This instrument has been recently proven to be sensitive enough to quantify halo phenomena in post-LASIK patients [6,16], being also useful to judge the improvement in visual performance after visual rehabilitation in complicated LASIK surgery [17]. As in previous reports, three consecutive measures were obtained from each subject, and then averaged prior to analysis.…”

“…After dark adaptation, each subject was asked to discriminate a small luminous source around a central high-luminance stimulus, following the methodology described in previous reports [6,16]. A distortion index, so-called LDI or luminous distortion, is obtained for assessing the effect of halos on night vision.…”

“…Although the room was in total darkness, the iluminance on the eye at the test distance due to the central source of light was 0.27 lux. LDI represents the area where stimuli are not seen due to light distortion caused by central source of light over the total area under evaluation, and is expressed as a percentage [6].…”

“…Villa et al [6] have shown correlations between halo phenomena (probably better referred to as light distortion [5]) and secondary astigmatism, coma and spherical aberration. However, there are more sources that contribute to light distortion [5], and retinal straylight could be one of those.…”