To analyze the origin of the changes in corneal asphericity (p-factor) after laser in situ keratomileusis (LASIK) and the effect of postsurgery asphericity on contrast-sensitivity function (CSF) under photopic conditions. Department of Optics, University of Granada, Granada, Spain. The p-factor and CSF (best corrected before surgery and 1, 3, and 6 months after surgery) were measured in 24 eyes. An increase in the p-factor after LASIK was noted; there was an 87.2% change in the asphericity using the paraxial formula of Munnerlyn and coauthors. Other factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea could account for the greater than expected increase (12.8%) in the p-factor. The CSF measurements deteriorated after LASIK; the change was significant (P<.05) in patients with myopia worse than -4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree. The increase in corneal asphericity after surgery, greater with a higher degree of myopia, and the deterioration in CSF with high myopia justify new ablation algorithms and further study of the variables that could modify the ablation unpredictably.

Aging leads to impaired visual function, which can affect driving—a very visually demanding task—and has a direct impact on an individual’s quality of life if their license is withdrawn. This study examined the associations between age-related vision changes and simulated driving performance. To this end, we attempted to determine the most significant visual parameters in terms of evaluating elderly drivers’ eyesight. Twenty-one younger drivers (aged 25–40) were compared to 21 older drivers (aged 56–71). Study participants were assessed for visual acuity, contrast sensitivity, halos, and intraocular straylight, which causes veiling luminance on the retina and degrades vision. Driving performance was evaluated using a driving simulator. The relationships between simulated driving performance and the visual parameters tested were examined with correlation analyses and linear regression models. Older drivers presented impairment in most visual parameters (p < 0.05), with straylight being the most significantly affected (we also measured the associated effect size). Older drivers performed significantly worse (p < 0.05) in the simulator test, with a markedly lower performance in lane stability. The results of the multiple linear regression model evidenced that intraocular straylight is the best visual parameter for predicting simulated driving performance (R² = 0.513). Older drivers have shown significantly poorer results in several aspects of visual function, as well as difficulties in driving simulator performance. Our results suggest that the non-standardized straylight evaluation could be significant in driver assessments, especially at the onset of age-related vision changes.

PURPOSE: To determine whether the eye’s optical quality is correlated to the visual discrimination capacity of patients treated with LASIK using two different ablation algorithms. METHODS: Visual discrimination was evaluated by the disturbance index under low illumination (Halo v1.0 software, Laboratory of Vision Sciences and Applications) in two groups of patients who underwent LASIK with two different ablation algorithms using the Allegretto Wave Eye-Q 400 Hz laser (WaveLight AG). In the first group (standard group; 30 eyes), corneal ablations were performed with the standard algorithm (preoperative spherical equivalent refraction −3.20±1.70 diopters [D]). In the second group (Q-optimized group; 38 eyes; spherical equivalent refraction −3.40±1.90 D), the ablations were made with the Q-optimized (F-CAT) algorithm. Optical quality of the eye was calculated by the Strehl ratio measured with a double-pass device (OQAS, Visiometrics SL). RESULTS: After LASIK, both the Strehl ratio as well as visual discrimination capacity diminished in both groups, although the changes were significantly greater in the standard group than in the Q-optimized group. CONCLUSIONS: A high correlation was found between the Strehl ratio and the disturbance index in patients who underwent LASIK, regardless of the ablation algorithm applied. Optical and visual deterioration were greater after standard ablation.

Cannabis is the most widely used illegal drug in the world. Limited information about the effects of cannabis on visual function is available, and more detail about the possible impact of visual effects on car driving is required. This study investigated the effects of smoking cannabis on vision and driving performance, and whether these effects are correlated. Twenty drivers and occasional users were included (mean (SE) age, 23.3 (1.0) years; five women). Vision and simulated driving performance were evaluated in a baseline session and after smoking cannabis. Under the influence of cannabis, certain visual functions such as visual acuity (p < 0.001), contrast sensitivity (p = 0.004) and stereoacuity (far, p < 0.001; near, p = 0.013) worsened. In addition, there was an overall deterioration of driving performance, with the task of keeping the vehicle in the lane proving more difficult (p < 0.05). A correlation analysis showed significant associations between driving performance and visual function. Thus, the strongest correlations were found between the distance driven onto the shoulder and stereoacuity, for near (ρ = 0.504; p = 0.001) and far distances (ρ = 0.408; p = 0.011). This study provides the first evidence to show that the visual effects of cannabis could impact driving performance, compromising driving safety. The results indicate that information and awareness campaigns are essential for reducing the incidence of driving under the influence of cannabis.

Purpose: Corneal and total higher order eye aberrations and their effects on visual function were compared in two groups subjected to different emmetropization techniques—refractive surgery (LASIK) and corneal refractive therapy (CRT). Methods: Twenty eyes of 11 patients and 22 eyes of 13 patients were examined in the CRT and LASIK groups, respectively. Mesopic contrast sensitivity function (CSF) was studied monocularly and binocularly in the two groups of patients undergoing CRT and LASIK who had approximately the same mean refractive error. Corneal asphericity and corneal and total aberrations were calculated, and the differences were analyzed between groups. Visual acuity, corneal and total ocular aberrations, corneal asphericity, and mesopic CSF were determined before and 3 months after treatment. Results: In both groups, corneal and total higher order aberrations increased after treatment, and the change in some Zernike coefficients was significant. Mesopic CSF diminished after treatment under monocular as well as binocular conditions, with the greatest decline being found in the CRT group under binocular conditions. Corneal asphericity also increased significantly in both groups, which was more accentuated in the CRT group. Conclusions: Both emmetropization techniques increased higher order ocular aberrations, implying a decline in the mesopic CSF. The increase in aberrations and the consequent deterioration in visual function was more marked in the CRT group. [ J Refract Surg. 2009;25:277–284.]