Alcohol effects on drivers' speed management: The influence of visual performance and road complexity.

OBJECTIVE: The aim of this work is to assess how drivers adapt their driving speed as a self-regulation mechanism when driving under the influence of alcohol (DUIA), and the influence of alcohol consumption, visual performance, road complexity, and personal traits. METHOD: Thirty one volunteers took part in the study. All of them underwent three experimental sessions: Baseline (no alcohol), Alcohol 1 (low-moderate dose), and Alcohol 2 (moderate-high dose). Vision was tested by means of contrast sensitivity and retinal straylight. Driving performance was assessed using a driving simulator. The difference between the driving speed and the speed limit was calculated in 10 road scenarios of different complexity. RESULTS: Drivers adapted their driving speed less (i.e., drove faster) in Alcohol 1 condition compared to Alcohol 2 (p = 0.007). This indicate that participants felt more confident under the influence of a low-moderate dose of alcohol. Participants with better contrast sensitivity drove faster (p = 0.021). The complexity of the road and other factors such as driving experience, gender, or DUIA frequency, also influenced speed choice. CONCLUSIONS: Drivers under the influence of a low-moderate dose of alcohol seem to be less aware of the risk. Contrast sensitivity is a good predictor of the speed choice when DUIA. A better understanding of drivers' behavior under the influence of substance use may be useful to adjust and improve the traffic laws and driving regulations.

Designing multifocal corneal models to correct presbyopia by laser ablation.

Two multifocal corneal models and an aspheric model designed to correct presbyopia by corneal photoablation were evaluated. The design of each model was optimized to achieve the best visual quality possible for both near and distance vision. In addition, we evaluated the effect of myosis and pupil decentration on visual quality. The corrected model with the central zone for near vision provides better results since it requires less ablated corneal surface area, permits higher addition values, presents stabler visual quality with pupil-size variations and lower high-order aberrations.

Visual evaluation of different multifocal corneal models for the correction of presbyopia by laser ablation.

PURPOSE: To evaluate the visual quality of two theoretical multifocal corneal models designed to correct presbyopia by corneal photoablation. METHODS: Two theoretical multifocal corneal surfaces were analyzed by ray tracing: a central model (with a central zone for near vision and a peripheral zone for distance vision), and a peripheral model (with a central zone for distance vision and a peripheral zone for near vision). For both models, the effect of the size of the central zone and transition zone as well as the size of the pupil was evaluated. RESULTS: Our results show that a smaller transition zone favors total visual quality in both models. The optimal size of the central zone depends both on the size of the transition zone used as well as the model. However, both models responded similarly with respect to the variations in pupil size, providing the same visual quality although in an opposite way. CONCLUSIONS: This work shows that the optimal diameter of the central zone is smaller for the central model than for the peripheral model. Also, pupil size plays a fundamental role in achieving multifocality, showing that patient's pupil size should be thoroughly evaluated prior to multifocal refractive surgery.

Binocular visual performance after LASIK.

PURPOSE: To analyze binocular visual function after LASIK. METHODS: Eye aberrometry and corneal topography was obtained for both eyes in 68 patients (136 eyes). To evaluate visual performance, monocular and binocular contrast sensitivity function and disturbance index for quantifying halos were measured. Tests were performed under mesopic conditions. RESULTS: Binocular summation and disturbance index diminished significantly (P<.0001) after LASIK with increasing interocular differences in corneal and eye aberrations. Binocular visual deterioration was greater than monocular deterioration for contrast sensitivity function and disturbance index. CONCLUSIONS: Binocular function deteriorates more than monocular function after LASIK. This deterioration increases as the interocular differences in aberrations and corneal shape increase. Improvements in ablation algorithms should minimize these interocular differences.

Differences between real and predicted corneal shapes after aspherical corneal ablation.

We study the differences between real and expected corneal shapes, using an aspherical ablation algorithm with a known equation and avoiding the limitation imposed by most studies of refractive surgery in which the ablation equations are not known. We have calculated the theoretical corneal shape predicted by this algorithm, comparing this shape with the real corneal topography. The results indicate that the deviations that appear in the corneal shape are significant for visual performance and for the correction of eye aberrations. If we include in this analysis the effect of reflection losses and nonnormal incidence on the cornea, we can reduce corneal differences, but they will remain significant. These results confirm that it is essential to minimize corneal differences to achieve effective correction in refractive surgery.